Progress 10/01/16 to 09/30/17

Outputs
Target Audience:My target audience includes plant breeders and scientists in the agricultural biotech industry. In addition, since the projects in my lab using sunflower are particularly appropriate for educating non-scientists about modern approaches to understanding plant physiology, I am also interested in engaging the general public. In the past year, I have reached out to these groups in various ways. I presented my lab's research in the UC Davis Seed Central "Discovery Series", a seminar series exclusively for companies affiliated with Seed Central. I also hosted a day-long visit of a class of sixth grade students to UC Davis. These students were from Washington Elementary School in midtown Sacramento, which serves a lower middle class, moderately educated neighborhood. Students toured the UC Davis Conservatory, extracted DNA from strawberries, and examined both plant cells and their own cheek cells under the microscope, thus introducing them to plant diversity and the commonalities between plants and animals. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Numerous training and professional development activities have been carried out during the past year. Dr. Harmer has helped train two post-docs (H. Atamian, N. Creux), two graduate students (C. Brooks and V. Thompson), nine undergraduate researchers, and three high school students. The more senior personnel (post-docs and graduate students) are helping supervise the undergraduate and high school researchers, giving them valuable mentoring experience. Two of the nine undergraduate students who worked on this project during the last year are members of under-represented minorities. One former intern is currently applying to graduate school, and two recently started doctoral programs. Two of the three high school students who worked on the project last summer joined the Harmer lab through the auspices of the Young Scholars Program (YSP). All undergraduate students carrying out independent research write up descriptions of research goals at the beginning of the semester and give a presentation in lab meeting at the end of the semester. Dr. Harmer holds weekly one-on-one meetings with the post-docs and the graduate student working on the project. During these meetings, progress on the project, future directions, mentoring issues and solutions, data analysis, writing, and career planning are discussed. Additional undergraduate students meet regularly with the post-docs or technicians who are directly supervising them and meet monthly with Dr. Harmer. Project participants were involved in a number of conferences, courses, and symposia. Three undergraduate and two high school students presented their research findings at campus-wide symposia at UC Davis. PI Harmer was invited to present her research at a number of international meetings and departmental seminars (Compositae workshop, Plant and Animal Genomes Conference, San Diego, CA, January 2017; UC Riverside, March, 2017; Seed Central "Discovery Series", UC Davis, April, 2017; Society for Developmental Biology meeting, Minneapolis, MN, July 2017; FASEB "Mechanisms in Plant Development" meeting, Saxtons River, VT, July, 2017; Gordon Research Conference "Chronobiology", Stowe, VT, July, 2017). Additionally, post-doc N. Creux presented her work on the UC Davis campus both at the Department of Plant Biology annual retreat in October 2017 and in the 2017 UC Davis Postdoctoral Research Symposium. She also presented her findings at the 2017 American Society for Plant Biology meeting (HI, July, 2017) Dr. Harmer takes the mentoring of trainees seriously, especially for post-doctoral scholars who will soon be looking for independent positions, meeting with them on a weekly to review not only short-term project goals but also longer-term strategic goals and their career objectives. She successfully mentored post-doc H. Atamian through a search for an academic position: Dr. Atamian has just started a new position as Assistant Professor at Chapman University. In addition, PI Harmer mentored Dr. Atamian through the preparation and submission of an NSF grant proposal exploring research areas he will focus on in his independent faculty position. All trainees are given constructive criticism after their research presentations to enhance their communication skills. As the project progresses, the post-docs and graduate students involved will continue to present their findings at national and international meetings and to write the manuscripts describing their work. How have the results been disseminated to communities of interest?We are working to communicate our findings with our target audience in different ways. First, PI Harmer continues to present the lab's work in workshops, international meetings, and departmental seminar series. These include the following presentations: at the 2017 Plant and Animal Genomes Conference (Compositae workshop), in the Seed Central "Discovery Series" at UC Davis (April, 2017); at the Society for Developmental Biology meeting (Minneapolis, MN, July 2017); at the FASEB "Mechanisms in Plant Development" meeting (Saxtons River, VT, July, 2017); and in the Gordon Research Conference "Chronobiology" meting (Stowe, VT, July, 2017). The Plant and Animal Genomes conference and the Seed Central series in particular had significant numbers of attendees from the biotech and ag industries. In addition, post-doc N. Creux presented her findings both on campus (at the Department of Plant Biology annual retreat in October 2017 and at the 2017 UC Davis Postdoctoral Research Symposium) and at an international meeting (American Society for Plant Biology, 2017). What do you plan to do during the next reporting period to accomplish the goals?During the next reporting period, we will continue to pursue our aims as follows. To better understand the physiological pathways underlying solar tracking, we will: 1) use RNA-seq to determine whether circadian gating of blue light signaling is responsible for the differential growth patterns that mediate solar tracking 2) use RNA-seq to identify genes acutely regulated by auxin at dawn and at dusk to better understand why auxin application disrupts daytime but not nighttime tracking movements 3) examine clock-related traits in plants identified from a TILLING population that have alterations within a sunflower homolog of ELF3, a gene implicated in clock regulation and flowering-time control in other species To better understand the effects of temperature on morning pollinator visits to flowers, we will: 1) characterize the effects of light on floral organ elongation and pollen release 2) investigate the molecular pathways involved in late-stage floral development using qRT-PCR In support of the above aims, we will also continue our efforts to optimize sunflower transformation protocols in collaboration with the labs of Drs. Ben Blackman and Loren Rieseberg.

Impacts
What was accomplished under these goals? The major goals of this research project are to better understand how external and internal factors interact to coordinate plant growth with a changing environment and how integration of these regulatory pathways help plants adapt to different environments. Our model crop is sunflower, which robustly modifies its growth in response to and in anticipation of light cues in a process called heliotropism, or solar tracking. We have found that perturbation of solar tracking reduces plant biomass and total leaf area by approximately 10% compared to control plants, demonstrating the importance of this process. In addition, we have shown the involvement of the circadian clock both in the daily solar tracking growth rhythms of young plants and in the characteristic eastward orientation of sunflower plants at maturity. We have focused on this latter trait during the period of review. We have found that the orientation of mature flowers affects the timing of pollen release and the male reproductive success of the plants. Thus, this work has important implications for both plant breeding and agronomic production. Our detailed analyses of solar tracking across development have revealed that plants are able to robustly solar track as soon as their epicotyls have emerged. This directional movement is produced by differential elongation of the east and west sides of the stem, with a greater growth rate on the east side during the day and on the west side during the night. Consistent with growth driving bending, as plants reach physiological maturity both elongation growth and bending movements gradually cease so that by the time the flowers are open the plants no longer undergo daily bending movements. Sunflowers are remarkable for the uniform eastward orientation of flowers seen across a field of mature plants. We have implicated the circadian clock in this phenomenon: we found that the ability of plants to bend towards light is much stronger in the morning than in the afternoon. Thus as plants reach floral maturity and stem elongation slows, their degree of bending towards the west becomes less and less each day and they ultimately do not deviate from their eastward position. Furthermore, we have found that eastward facing plants are more attractive to pollinating insects than westward facing plants. Our work over the past year has focused on the physiological mechanisms underlying this insect preference and we have made several exciting discoveries into the ways internal and external cues control floral development. First, we have found that pollen is released earlier on east-facing than west-facing flowers, and have used male-sterile plants to demonstrate that insect preferences for east-facing plants depends upon pollen release. We found the earlier pollen release is due to the warmer temperatures of east-facing compared to west-facing plants in the morning; these warmer temperatures cause faster elongation of anther filaments and styles. In related studies, we have demonstrated that floral organ elongation and pollen release are controlled both by the circadian clock and by light signaling pathways. Intriguingly, rhythms in pollen release continue in constant darkness but pollen release is completely inhibited in constant light. In contrast, stigma exsertion is inhibited in constant darkness but persists in constant light conditions. Finally, interruption of the night with light pulses causes aberrant timing of pollen release and style elongation.

Publications

• Type: Journal Articles Status: Published Year Published: 2017 Citation: Harmer, S.L., and Brooks, C.J. (2017) Growth-mediated plant movements: hidden in plain sight. Current Opinion in Plant Biology. 41:89-94. doi: 10.1016/j.pbi.2017.10.003.
• Type: Journal Articles Status: Published Year Published: 2017 Citation: Rubin, M.J., Brock, M.T., Davis, A.M., German, Z.M., Welch, S.M., Harmer, S.L., Maloof, J.N., Davis, S.J., and Weinig, C. (2017) Circadian rhythms vary over the growing season and correlate with fitness components. Molecular Ecology. 26(20):5528-5540. doi: 10.1111/mec.14287.
• Type: Journal Articles Status: Accepted Year Published: 2017 Citation: Gray, J.A., Shalit-Kaneh, A., Chu, D.N., Hsu, P.Y., and Harmer, S.L. (2017) The REVEILLE clock genes inhibit growth of juvenile and adult plants by control of cell size. Plant Physiology. 173(4):2308-2322. doi: 10.1104/pp.17.00109.

Progress 10/01/15 to 09/30/16

Outputs
Target Audience:My target audience includes plant breeders and scientists in the agricultural biotech industry. In addition, since the projects in my lab using sunflower are particularly appropriate for educating the public about modern approaches to understanding plant physiology, I am interested in also engaging the general public. In the past year, I have reached out to these groups in various ways. I presented my research findings in a seminar at the Woodland Monsanto site later this year. I have also been very active in outreach efforts to the general public, participating in interviews with a number of reporters for print and radio outlets. Our work has received a great deal of coverage in the popular press, including pieces in the New York Times, The Washington Post, and the Atlantic. A more complete list of press coverage may be found at http://www.openwetware.org/wiki/Sunflower_press_summary. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Numerous training and professional development activities have been carried out during the past year. Dr. Harmer has helped train two post-docs (H. Atamian, N. Creux), one graduate students (C. Brooks), eleven undergraduate researchers, and four high school students. The more senior personnel (post-docs and the graduate student) are helping supervise the undergraduate and high school researchers, giving them valuable mentoring experience. Four of the eleven undergraduate and two of the four high school scholars who worked on this project during the last year are members of under-represented minorities. One undergraduate student completed an honors thesis during spring quarter, 2016. One former intern is currently applying to graduate school, two recently started doctoral programs, one is currently a lab technician at UCSF, and two currently hold industry jobs. Two of the four high school students who worked on the project last summer joined the Harmer lab through the auspices of the Young Scholars Program (YSP) and one completed a Future Farmers of America (FFA) internship in the lab. All undergraduate students carrying out independent research write up descriptions of research goals at the beginning of the semester and give a presentation in lab meeting at the end of the semester. Dr. Harmer holds weekly one-on-one meetings with the post-docs and the graduate student working on the project. During these meetings, progress on the project, future directions, mentoring issues and solutions, data analysis, writing, and career planning are discussed. Additional undergraduate students meet regularly with the post-docs or technicians who are directly supervising them and meet monthly with Dr. Harmer. Project participants were involved in a number of conferences, courses, and symposia. Four undergraduate and two high school students presented their research findings at campus-wide symposia at UC Davis. PI Harmer taught at the Cold Spring Harbor "Frontiers and Techniques in Plant Science" summer course and was invited to present her research at several international meetings and departmental seminars (Gordon Research Conference "Photosensory Receptors", TX; January 2016; University of Heidelberg, Heidelberg, Germany; March 2016; University of Pennsylvania, Philadelphia, PA; March 2016; and The Danforth Plant Science Center, St. Louis, MO; May 2016). Additionally, post-docs N. Creux and H. Atamian presented their work at the Department of Plant Biology annual retreat in October 2016 and Dr. Atamian also gave a talk at the 2016 UC Davis Postdoctoral Research Symposium. Dr. Harmer takes the mentoring of trainees seriously, especially for post-doctoral scholars who will soon be looking for independent positions, meeting with them on a weekly to review not only short-term project goals but also longer-term strategic goals and their career objectives. Dr. Creux recently wrote a draft of a review article, and she and the PI are now collaboratively revising this document. Dr. Atamian has had a number of Skype and in-person interviews for professorial positions. He has given practice job talks to members of the Harmer lab and received extensive feedback on ways to improve his presentation. In addition, PI Harmer mentored Dr. Atamian through the preparation and submission of an NSF grant proposal exploring research areas he plans to focus on when he obtains an independent faculty position. All trainees are given constructive criticism after their research presentations to enhance their communication skills. As the project progresses, the post-docs and graduate students involved will continue to present their findings at national and international meetings and to write the manuscripts describing their work. How have the results been disseminated to communities of interest?During the past year some of our results were published in a report featured on the cover of Science magazine. This afforded us numerous opportunities for outreach to the general public. PI Harmer was featured in radio interviews on programs such as the BBC World Service "Science in Action" and was interviewed by reporters from The New York Times, The Atlantic, and The Washington Post, among others. Post-doc Atamian was featured in a television piece appearing in Decouverte, a science program produced by Radio-Canada-Television. A more complete list of coverage of our work in the popular press may be found here: http://openwetware.org/wiki/Sunflower_press_summary. PI Harmer also presented work resulting from this proposal in a seminar at Monsanto, Woodland, CA (February, 2016). What do you plan to do during the next reporting period to accomplish the goals?During the next reporting period, we will continue to pursue our aims as follows. To better understand the physiological pathways underlying solar tracking, we will: 1) use RNA-seq to determine whether circadian gating of blue light signaling is responsible for the differential growth patterns that mediate solar tracking 2) use RNA-seq to identify genes acutely regulated by auxin at dawn and at dusk to better understand why auxin application disrupts daytime but not nighttime tracking movements 3) in collaboration with the Sakakibara lab (RIKEN, Japan), monitor hormone levels on opposite sides of solar tracking stems at two-hour resolution over a day/night cycle To better understand the effects of temperature on morning pollinator visits to flowers, we will: 1) characterize the volatile emission profiles of east- and west-facing sunflowers 2) examine the effects of temperature on the timing of pollen exsertion 3) investigate the effects of light on floret maturation and pollen release 4) investigate the relationship between pollination timing and pollen precedence In support of the above aims, we will also continue our efforts to optimize sunflower transformation protocols. We are currently working to enhance rooting and decrease false positive selection by using different selective agents such as kanamycin and phosphite. We will also try NAA pulse protocols to try to improve rooting efficiency. The next step will be to test other promoters and work towards generating transgenic plants carrying the DR5 auxin-responsive synthetic promoter controlling a luciferase reporter gene to further investigate the role of auxin and the circadian clock in heliotropism and floret development. Furthermore, these techniques will allow us to stably silence candidate genes implicated in solar tracking and to introduce other reporter genes into sunflower. Finally, we will characterize plants isolated from a TILLING population that have alterations in selected genes likely involved in heliotropism.

Impacts
What was accomplished under these goals? The major goals of this research project are to better understand how external and internal factors interact to coordinate plant growth with a changing environment and how integration of these regulatory pathways help plants adapt to different environments. Our model crop is sunflower, which robustly modifies its growth in response to and in anticipation of light cues in a process called heliotropism, or solar tracking. We have found that perturbation of solar tracking reduces plant biomass and total leaf area by approximately 10% compared to control plants, demonstrating the importance of this process. In addition, we have shown the involvement of the circadian clock both in the daily solar tracking growth rhythms of young plants and in the characteristic eastward orientation of sunflower plants at maturity. Our studies on the molecular and physiological bases of these processes and their ecological and agronomic consequences are described below. Our detailed analyses of solar tracking across development have revealed that plants are able to robustly solar track as soon as their epicotyls have emerged. This directional movement is produced by differential elongation of the east and west sides of the stem, with a greater growth rate on the east side during the day and on the west side during the night. We performed time course transcriptome analysis over two days and nights to identify genes with differential expression on the east and west sides of solar tracking stems. We found only a few dozen differentially expressed genes. In most cases, the time of differential gene expression correlates with daily growth rhythms; that is, genes more highly expressed on the east side of the stem tend to have peak expression in the late afternoon whereas those more highly expressed on the west side of the stem tend to have peak expression during the night. In many cases, the Arabidopsis homologs of these genes have previously been implicated in growth regulation. Furthermore, Gene Ontology analysis reveals an overrepresentation of genes involved in auxin signaling and response. Thus our data suggest that clock and light modulation of auxin signaling underlie solar tracking behavior. To functionally test the role of auxin in solar tracking, we have applied the synthetic auxin 2,4-D either uniformly around stems or only on the east- or west-facing sides of stems at different times of the day or night. Analysis of time-lapse videos reveals that auxin application during the day quickly perturbs stem movement patterns but that auxin application during the night has no immediate effect on solar tracking. Gene expression studies indicate that this is not due to a general inability of the plants to respond to exogenous auxin at night, suggesting circadian gating of a subset of auxin responses. However, experiments in which we applied the auxin transport inhibitor NPA at different times of the day or night indicate that auxin transport is required for both daytime and nighttime movements. Together, these data suggest that auxin signaling may be instructive for the daytime but only permissive for the nighttime movements of solar tracking plants. Furthermore, we found that the range of bending movement at night appears to be set by the range of movement generated during daytime hours. We are now investigating the possibility that different growth pathways govern daytime and nighttime solar tracking movements. In our published work, we demonstrated the involvement of the circadian system in the uniform eastward orientation of mature sunflower inflorescences. We also found that pollinating insects prefer east-facing over west-facing flowers We are currently investigating the physiological effects of sunflower head orientation on bud opening, floral organ maturation, pollen dehiscence and volatile emissions. We have found that that east-facing buds open sooner and at a faster rate than those on west-facing inflorescences and that the phase of pollen dehiscence is advanced by an hour in east- versus west-facing inflorescences. Finally, volatile sampling in the field followed by GC-MS analysis revealed that east-oriented sunflowers emit larger amounts of important floral volatile compounds such as beta-calarene than west-facing flowers. The increased morning temperature and earlier release of volatiles and pollen likely all contribute to make east-facing flowers more attractive to pollinators than west-facing flowers

Publications

• Type: Journal Articles Status: Published Year Published: 2016 Citation: Atamian, H.S., and Harmer, S.L. (2016) Circadian regulation of hormone signaling and plant physiology. Plant Molecular Biology. 91(6):691-702. doi: 10.1007/s11103-016-0477-4.
• Type: Journal Articles Status: Published Year Published: 2016 Citation: M�ller-Moul� P, Nozue K, Pytlak ML, Palmer CM, Covington MF, Wallace AD, Harmer SL, Maloof JN. (2016) YUCCA auxin biosynthetic genes are required for Arabidopsis shade avoidance. PeerJ 4:e2574 https://doi.org/10.7717/peerj.2574
• Type: Journal Articles Status: Published Year Published: 2016 Citation: Atamian, H.S., Creux, N.M., Brown, E.A., Garner, A.G., Blackman, B.K., and Harmer, S.L. (2016) Circadian regulation of sunflower heliotropism, floral orientation, and pollinator visits. Science. 353(6299):587-90. doi: 10.1126/science.aaf9793.

Progress 10/01/14 to 09/30/15

Outputs
Target Audience:My target audience includes plant breeders and scientists in the agricultural biotech industry. In addition, since the projects in my lab using sunflower are particularly appropriate for educating the public about modern approaches to understanding plant physiology, I am interested in also engaging the general public. In the past year, I have reached out to these groups in various ways. I have interacted with undergraduate and graduate students at UC Davis as an instructor of my regularly scheduled classes, as an invited speaker in the College of Biological Science's "Road to Research" seminar series, as a speaker in a career panel for the Women in Science and Engineering mentoring program, and as a mentor for the many high school, undergraduate, and graduate students carrying out original research in my lab. In support of the new research program in my lab, I have initiated a collaboration with Dr. Brent Hulke, a USDA research geneticist who studies sunflower. I have given a number of invited seminars at international conferences and at university departmental seminars. Finally, I have arranged to present my research findings in a seminar at the Woodland Monsanto site later this year. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Numerous training and professional development activities have been carried out during the past year. Dr. Harmer has helped train two post-docs (H. Atamian, N. Creux), two graduate students (J. Gray and V. Fanelli), fifteen undergraduate researchers, and three high school students. The more senior personnel (post-docs, technicians, and graduate student) are helping supervise the undergraduate and high school researchers, giving them valuable mentoring experience. Three of the fifteen undergraduate scholars who worked on this project during the last year are members of under-represented minorities and three undergraduates completed honors theses during spring quarter, 2015. One student is currently applying to graduate schools and two others are applying to professional schools. Two of the three high school students who worked on the project joined the Harmer lab through the auspices of the Young Scholars Program (YSP). All undergraduate students carrying out independent research write up descriptions of research goals at the beginning of the semester and give a presentation in lab meeting at the end of the semester. Dr. Harmer holds weekly one-on-one meetings with the post-docs and the graduate student working on the project. During these meetings, progress on the project, future directions, mentoring issues and solutions, data analysis, writing, and career planning are discussed. Additional undergraduate students meet regularly with the post-docs or technicians who are directly supervising them and meet monthly with Dr. Harmer. Project participants were involved in a number of conferences, courses, and symposia. Post-docs N. Creux and H. Atamian have been participating in the year-long "Professors for the Future" fellowship program at UC Davis to develop leadership skills and prepare themselves for the job market. Post-doc Dr. Atamian presented a poster describing his work at the American Society for Plant Biology meeting (July, 2015). Five undergraduate and two high school students presented their research findings at campus-wide symposia at UC Davis. PI Harmer taught at the Cold Spring Harbor "Frontiers and Techniques in Plant Science" summer course and was invited to present her research international meetings and departmental seminars (Plant Biology seminar, U Mass Amherst, March 2015; the International Symposium on Plant Photobiology, May 2015; and the Gordon Conference on Chronobiology, July 2015). PI Harmer also gave an invited presentation at the NSF "Plant Genome Research Program" meeting (September, 2015). Dr. Harmer takes the mentoring of trainees seriously, especially for post-doctoral scholars who will soon be looking for independent positions, meeting with them on a weekly to review not only short-term project goals but also longer-term strategic goals and their career objectives. Dr. Atamian recently wrote the first draft of a review article and he and the PI are now collaboratively revising this document. All trainees are given constructive criticism after their research presentations to enhance their communication skills. As the project progresses, the post-docs and graduate students involved will continue to present their findings at national and international meetings and to write the manuscripts describing their work. How have the results been disseminated to communities of interest?My target audience includes plant breeders and scientists in the agricultural biotech industry. In addition, since the projects in my lab using sunflower are particularly appropriate for educating the public about modern approaches to understanding plant physiology, I am interested in also engaging the general public. In the past year, I have reached out to the general public, and to plant scientists in both the private and academic sectors. I have interacted with students at UC Davis as an invited speaker in the College of Biological Science's "Road to Research" seminar series, as a speaker in a career panel for the Women in Science and Engineering mentoring program, and as a mentor for the many high school, undergraduate, and graduate students carrying out original research in my lab. In support of the new research program in my lab, I have initiated a collaboration with Dr. Brent Hulke, a USDA research geneticist who studies sunflower. I have given a number of invited seminars at international conferences and at university departmental seminars. Finally, I have arranged to present my research findings in a seminar at the Woodland Monsanto site later this year. Other members of my lab have also been involved in outreach efforts. Post-doc N. Creux presented project results at the UC Davis Lab and Research Fair, an outreach effort aimed at recruiting undergraduate students from diverse backgrounds to carry out research in campus labs. Post-doc Dr. Atamian presented a poster describing his work at the American Society for Plant Biology meeting (July, 2015). Five undergraduate and two high school students presented their research findings at campus-wide symposia at UC Davis. What do you plan to do during the next reporting period to accomplish the goals?During the next reporting period, we will continue to investigate how the circadian clock interacts with environmental cues to regulate plant growth, with a focus on solar tracking in sunflower. To better understand the physiological pathways underlying solar tracking, we will: 1) use RNA-seq to determine whether circadian gating of blue light signaling is responsible for the differential growth patterns that mediate solar tracking 2) determine whether accessions with atypical floral head positioning at anthesis have altered clock gating of phototropic responses 3) in collaboration with the Sakakibara lab (RIKEN, Japan), monitor hormone levels on opposite sides of solar tracking stems over two successive days To better understand the effects of temperature on morning pollinator visits to flowers, we will: 1) characterize the volatile emission profiles of east- and west-facing sunflowers 2) examine the effects of temperature on the timing of pollen exsertion In support of all of the above aims, we will also continue our efforts to develop sunflower transformation protocols. These techniques will allow us to stably silence candidate genes implicated in solar tracking and to introduce reporter genes into sunflower. We will also screen a TILLING population for mutants disrupted in selected genes likely involved in heliotropism.

Impacts
What was accomplished under these goals? The major goals of this research project are to better understand how external and internal factors interact to coordinate plant growth with a changing environment and how integration of these regulatory pathways help plants adapt to different environments. Our model crop is sunflower, which robustly modifies its growth in response to and in anticipation of light cues in a process called heliotropism, or solar tracking. We have found that perturbation of solar tracking reduces plant biomass and total leaf area by approximately 10% compared to control plants, demonstrating the importance of this process. In addition, we have shown the involvement of the circadian clock both in the daily solar tracking growth rhythms of young plants and in the characteristic eastward orientation of sunflower plants at maturity. Our studies on the molecular and physiological bases of these processes and their ecological and agronomic consequences are described below. Our detailed analyses of solar tracking across development have revealed that plants are able to robustly solar track as soon as their epicotyls have emerged. This directional movement is produced by differential elongation of the east and west sides of the stem, with a greater growth rate on the east side during the day and on the west side during the night. We performed time course transcriptome analysis over two days and nights to identify genes with differential expression on the east and west sides of solar tracking stems. We found only a few dozen differentially expressed genes. In most cases, the time of differential gene expression correlates with daily growth rhythms; that is, genes more highly expressed on the east side of the stem tend to have peak expression in the late afternoon whereas those more highly expressed on the west side of the stem tend to have peak expression during the night. In many cases, the Arabidopsis homologs of these genes have previously been implicated in growth regulation. Furthermore, Gene Ontology analysis reveals an overrepresentation of genes involved in auxin signaling and response. Thus our data suggest that clock and light modulation of auxin signaling underlie solar tracking behavior. To determine whether solar tracking affects yield-associated traits of sunflower plants, we disrupted heliotropism in field-grown plants by two different methods and then examined the effects on vegetative development. First, we tied sunflower stems to solid supports to prevent daily stem movements. Second, we grew plants in pots and rotated the experimental pots 180 every night such that plant apices faced east rather than west. In both type of experiment, we found that the leaf area and biomass of the experimental samples were significantly reduced relative to the controls, demonstrating the importance of solar tracking to sunflower plants throughout development. We have also investigated the cessation of movements as plants mature and found that flower heads permanently face east at anthesis because the apices move progressively less each successive afternoon and evening as stem elongation ceases. We examined the ecological function of mature head orientation by growing plants in pots until anthesis and then rotating pots or staking plants to generate different orientation treatments. We found that eastward facing plants warm up earlier in the day than plants facing other orientations. We further observed a small but statistically significant effect of head orientation on both final head diameter and seed weight, with east-facing flowers larger than west-facing flowers. Intriguingly, we observed a strong and significant elevation in morning pollinator visitation to eastward facing plants relative to plants facing other orientations. This pollinator preference could be largely overcome by using parabolic heaters to raise the temperature of the west-facing flowers to match that of the east-facing flowers.

Publications

• Type: Journal Articles Status: Published Year Published: 2015 Citation: Brady, S.M, Burow, M., Busch, W., Carlgborg, O., Denby, K.J., Glazebrook, J., Hamilton, E.S., Harmer, S.L., Haswell, E.S., Maloof, J.N., Springer, N.M., and Kliebenstein, D.J. (2015) Reasses the t Test: Interact with all your data via ANOVA. Plant Cell 27(8): 2088-94. doi: 10.1105/tpc.15.00238
• Type: Journal Articles Status: Published Year Published: 2015 Citation: Jones, M.A., Hu, W., Litthauer, S., Lagarias, J.C., and Harmer, S.L. (2015) A constitutively active allele of phytochrome B maintains circadian robustness in the absence of light. Plant Physiology 169(1): 814-825. doi: 10.1104/pp.15.00782