Progress 10/01/99 to 09/30/04
Outputs
This project had two major objectives. The first was to characterize patterns of macrohair initiation during leaf development. The second objective was to clone and characterize the genes, particularly macrohairless1, that program macrohair initiation in maize. The first objective is completed and significant progress has been made toward the second. Macrohairs are the first cell type to differentiate within leaf epidermis and initiate in a highly organized pattern. Macrohairs form in files of epidermal cells regularly spaced relative to the developing vascular system, demonstrating that cellular differentiation within the leaf responds to signals that are transmitted from internal cellular layers. Within the files of macrohairs, macrohair initiation is always separated by at least one and usually two cells, indicating that differentiation of one macrohair cell inhibits the initiation of a macrohair in adjacent cells. Macrohair initiation is repressed by the glossy15
gene that maintains juvenile development, but is promoted by the gibberrellic acid class of plant growth regulators that induce adult development. Within developing adult leaves, macrohair initiation occurs in a small region at the base of the leaf and macrohair density within the leaf progressively declines during shoot development. These observations suggest that the signals which induce macrohair differentiation act during early leaf development, are locally mobile, and are modified by factors that define when epidermal cells are competent to differentiate. These descriptions of macrohair formation and its genetic control were reported in Moose et al. (2003). Three complementary approaches have been employed to clone genes that program macrohair initiation. The first approach involves the cloning of the macrohairless1 (mhl1) gene via Mutator transposon tagging. Candidate Mutator transposon fragments have been identified that co-segregate with a mhl1 mutant allele recovered from a
targeted mutagenesis experiment. The DNA flanking this transposon insertion is likely to represent a portion of the mhl1 gene. The second approach is to associate molecular markers with variation for macrohair density in the intermated B73 x Mo17 recombinant inbred mapping population. A large amount of detailed phenotypic data on leaf epidermal cell differentiation has been collected and is now being associated with the molecular marker data already available for this population. Tightly-linked molecular markers that flank the mhl1 locus have also been identified that will allow direct tests for the contribution of the mhl1 gene to quantitative variation in macrohair initiation frequency. The final strategy involves identifying maize genes that are homologous to genes from Arabidopsis that are known to function in macrohair (trichome) initiation, which are being mapped and characterized for gene expression differences to determine if they are associated with either mhl1 or one of the
quantitative trait loci identified in the B73 x Mo17 mapping experiment.
Impacts
Hairs or trichomes are present on the leaves of most plant species and have been implicated as important factors in resistance to insect pests. In corn, the large leaf macrohairs are a marker for the adult phase of vegetative development and occur in a highly regulated pattern within the leaf epidermis. Little is known about the physiological function of corn leaf macrohairs or the molecular genetic mechanisms that contribute to their patterning within the leaf. The corn macrohairless1 mutation results in the failure to form macrohairs on the leaf surface, which provides an entry point into understanding how macrohairs develop and function. This project aims to molecularly clone the gene corresponding to the macrohairless1 mutation and characterize how it functions to promote macrohair formation. The findings from this work will increase our understanding of cellular differentiation within the corn leaf epidermis, which may offer novel strategies to modify leaf
epidermal traits for improved drought tolerance and insect resistance.
Publications
- Moose, S.P., Lauter, N. and Carlson, S. 2003. The maize macrohairless locus specifically promotes leaf blade macrohair initiation in response to factors regulating leaf identity. Genetics 166: 1451-1461.
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Progress 01/01/03 to 12/31/03
Outputs
This research has two major objectives. The first is to characterize the spatial and temporal patterns of macrohair initiation during leaf development to understand the developmental processes that lead to the highly organized patterns of cellular differentiation within the corn leaf epidermis. The second objective is to clone and characterize the genes, particularly macrohairless1, that program macrohair initiation in corn. During the past year progress has been made toward each of these objectives. Macrohairs are the first cell type to differentiate within leaf epidermis and initiate in a highly organized pattern. Macrohairs form in files of epidermal cells at regularly spaced intervals relative to the developing vascular system, demonstrating that celluar differentiation within the leaf responds to signals that are transmitted from internal cellular layers. Within the files of macrohairs, macrohair initiation is always separated by at least one and usually two
cells, indicating that differentiation of one macrohair cell inhibits the initiation of a macrohair in adjacent cells. Macrohair initiation is repressed by the glossy15 gene that activates juvenile development, but is promoted by gibberrellic acids which induce adult development. Within developing adult leaves, macrohair initiation occurs in a narrowly-defined window at the base of the leaf and macrohair density within the leaf progressively declines during shoot development. These observations indicate that the signals which induce macrohair differentiation act during early leaf development, are locally mobile through the vascular system, and are modified by factors that define when epidermal cells are competent to differentiate. Three complementary approaches are being employed to clone genes that program macrohair initiation. The most direct approach involves the cloning of the macrohairless1 (mhl1) gene via Mutator transposon tagging. A Mutator transposon fragment has been
identified that co-segregates with a mhl1 mutant allele recovered from a targeted mutagenesis experiment. The DNA flanking this transposon insertion is likely to represent a portion of the mhl1 gene. The second approach is to associate molecular markers with the high degree of variation for macrohair density in the intermated B73 x Mo17 recombinant inbred mapping population. A large amount of detailed phenotypic data on leaf epidermal cell differentiation was collected and is now being associated with the molecular marker data already available for this population. Tightly-linked molecular markers that flank the mhl1 locus have been identified that will allow direct tests for the contribution of the mhl1 gene to quantitative variation in macrohair initiation frequency. The final strategy involves identifying maize genes that are homologous to genes from Arabidopsis that function in macrohair (trichome) initiation, which are being mapped and characterized for gene expression
differences to determine if they are associated with either mhl1 or one of the quantitative trait loci identified in the B73 x Mo17 mapping experiment.
Impacts
Hairs or trichomes are present on the leaves of most plant species and have been implicated as important factors in resistance to insect pests. In corn, the large leaf macrohairs are a marker for the adult phase of vegetative development and occur in a highly regulated pattern within the leaf epidermis. Little is known about the physiological function of corn leaf macrohairs or the molecular genetic mechanisms that contribute to their patterning within the leaf. The corn macrohairless1 mutation results in the failure to form macrohairs on the leaf surface, which provides an entry point into understanding how macrohairs develop and function. This project aims to molecularly clone the gene corresponding to the macrohairless1 mutation and characterize how it functions to promote macrohair formation. The findings from this work will increase our understanding of cellular differentiation within the corn leaf epidermis, which may offer novel strategies to modify leaf
epidermal traits for improved drought tolerance and insect resistance.
Publications
- Moose, S.P., Lauter, N. and Carlson, S. 2003. The maize macrohairless locus specifically promotes leaf blade macrohair initiation in response to factors regulating leaf identity. Genetics (In Press).
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Progress 01/01/02 to 12/31/02
Outputs
This research has two major objectives. The first is to characterize the spatial and temporal patterns of macrohair initiation during leaf development to understand the developmental processes that lead to the highly organized patterns of cellular differentiation within the corn leaf epidermis. The second objective is to clone and characterize the genes, particularly macrohairless1, that program macrohair initiation in corn. During the past year progress has been made toward each of these objectives. Macrohairs are the first cell type to differentiate within leaf epidermis and initiate in a highly organized pattern. Macrohairs form in files of epidermal cells at regularly spaced intervals relative to the developing vascular system, which demonstrates that celluar differentiation within the leaf responds to signals that are transmitted from internal cellular layers. Within the files of macrohairs, macrohair initiation is always separated by at least one and usually two
cells, which indicates that differentiation of one macrohair cell inhibits the initiation of a macrohair in adjacent cells. Macrohair initiation is repressed by the glossy15 gene that activates juvenile development, but is promoted by gibberrellic acids which induce adult development. Within developing adult leaves, macrohair initiation occurs in a narrowly-defined window at the base of the leaf and macrohair density within the leaf progressively declines during shoot development. These observations indicate that the signals which induce macrohair differentiation act during early leaf development, are locally mobile through the vascular system, and are modified by factors that define when epidermal cells are competent to differentiate. Three complementary approaches are being employed to clone genes that program macrohair initiation. The most direct approach involves the cloning of the macrohairless1 (mhl1) gene via Mutator transposon tagging. A Mutator transposon fragment was
identified that co-segregates with a mhl1 mutant allele recovered from a targeted mutagenesis experiment. The DNA flanking this transposon insertion is likely to represent a portion of the mhl1 gene. The second approach is to associate molecular markers with the high degree of variation for macrohair density in the intermated B73 x Mo17 recombinant inbred mapping population. A large amount of detailed phenotypic data on leaf epidermal cell differentiation was collected this past summer and is now being associated with the molecular marker data already available for this population. Tightly-linked molecular markers that flank the mhl1 locus were identified that will allow direct tests for the contribution of the mhl1 gene to quantitative variation in macrohair initiation frequency. The final strategy involves identifying corn genes that are homologous to genes from Arabidopsis that function in macrohair (trichome) initiation, which are being mapped and characterized gene expression
differences to determine if they are associated with either mhl1 or one of the quantitative trait loci identified in the B73 x Mo17 mapping experiment.
Impacts
Hairs or trichomes are present on the leaves of most plant species and have been implicated as important factors in resistance to insect pests. In corn, the large leaf macrohairs are a marker for the adult phase of vegetative development and occur in a highly regulated pattern within the leaf epidermis. Little is known about the physiological function of corn macrohairs or the molecular genetic mechanisms that contribute to their patterning within the leaf. The macrohairless1 mutation in corn results in the failure to form macrohairs on the leaf surface, which provides an entry point into understanding how macrohairs develop and function. This research aims to molecularly clone the gene corresponding to the macrohairless1 mutation and characterize how it functions to promote macrohair formation. The findings from this research will increase our understanding of cellular differentiation within the corn leaf epidermis, which may offer novel strategies to modify leaf
epidermal traits for improved insect resistance.
Publications
- No publications reported this period
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Progress 01/01/01 to 12/31/01
Outputs
The corn macrohairless1 (mhl1) mutation results in the failure to form macrohairs on the leaf surface. This research has three major objectives related to the study of mhl1. The first is to characterize in detail the phenotypic effects of mhl1 during leaf development. The second is to investigate the effects of genetic background on macrohair (MH) development. The third objective is to molecularly clone the Mhl1 gene using mhl1 alleles obtained from a Mutator transposon-tagging experiment. A comprehensive survey of leaf MH density between different leaves of the same plant and within the leaf itself has revealed that MH density varies during shoot development and position within the leaf. In the W64A inbred, MH first appear at the base of leaf 7 and increase in density through leaf 9 where MH density peaks at approximately 135 MH/cm2. After leaf 9 there is a progressive decline in MH density. Within the fully mature ninth leaf blade of W64A, MH density was
significantly greater at the base compared to the tip of the leaf and is also higher near the midrib compared to the margin. These observations provide clues to either the distribution of signals that induce MH differentiation or the developmental window where cells become competent to acquire a MH identity. Major differences in MH density were also observed among corn inbred lines. As an example, MH density at the base of leaf 9 was 115.4 MH/cm2 for B73 and 280.0 MH/cm2 for Mo17. Interestingly, B73 did not show significant differences within the proximal-distal axis of the leaf blade. The differences in MH density between B73 and Mo17 are an important finding because they will allow the dissection of this apparently quantitative trait in the B73 x Mo17 mapping population where more than 1,000 molecular markers have already been placed on the map. Scanning electron microscopy of developing leaves from normal plants and three different mutant alleles of mhl1 has demonstrated that mhl
conditions a specific defect in macrohair initiation. This observation is important because it indicates that Mhl1 is a key gene in integrating signals that pattern cellular differentiation within the leaf epidermis to the program of MH formation. A Mutator transposon-tagging experiment generated four confirmed alleles of mhl1, which crossed twice to the W64A inbred to generate families segregating for mhl1. For each putatively Mutator-tagged mhl1 allele, at least 50 individuals within these families have been phenotyped and genomic DNAs prepared for co-segregation analyses with Mutator transposon sequences. Thus, all of the appropriate genetic materials and DNA samples were generated to clone genomic DNA corresponding to a portion of the Mh1l gene.
Impacts
Hairs or trichomes are present on the leaves of most plant species and have been implicated as important factors in resistance to insect pests. In corn, the large leaf macrohairs are a marker for the adult phase of vegetative development and occur in a highly regulated pattern within the leaf epidermis. Little is known about the physiological function of corn macrohairs or the molecular genetic mechanisms that contribute to their patterning within the leaf. The macrohairless 1 mutation in corn results in the failture to form macrohairs on the leaf surface. This reesarch aims to molecularly clone the gene corresponding to the macrohairless 1 mutation and characterize how it functions to promote macrohair formation. The findings from this work will increase our understanding of cellular differentiation within the corn leaf epidermis, which may offer novel strategies to modify leaf epidermal traits for improved insect resistance.
Publications
- No publications reported this period
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