| Summary: | The hooded mutant of sweet pea (Lathyrus odoratus) was characterized in order to better understand the genetic control of petal morphology in papilionoid legumes. The TCP identity gene CYCLOIDEA2 (CYC2) was shown to have different amplification patterns in the standard petals of hooded and wild-type sweet peas in RT-PCR experiments. Lathyrus CYC1 was also examined, but no differences were found between expression patterns in wild-type and hooded plants. Genome walking and additional sequencing revealed that the hooded phenotype was associated with a mutant allele of CYC2. To determine if the mutant allele of CYC2 is responsible for the hooded phenotype, a F2 segregation experiment was conducted. In a population of 118 plants, the hooded phenotype segregated with the mutant allele of CYC2 100% of the time, suggesting that the mutation in CYC2 is likely responsible for the hooded floral character. Scanning Electron Microscopy was conducted to determine if epidermal cell types could be used as micromorphological markers for petal identity. Cells on the adaxial surface of sweet pea petals can be used to distinguish petal identity. When mutant and wild-type flowers were compared, clear differences in cell type were observed. The standard petal in hooded flowers has taken on wing petal characteristics, indicating that the mutation is caused by a shift in petal identity. To examine localized growth patterns in wild-type and hooded flowers, microscopic grids were printed on the surfaces of sweet pea buds using a specialized inkjet apparatus. The deformation of the printed grid during growth allowed localized patterns of growth to be visualized. Wild-type standard petals have a more uniform rate of growth, whereas hooded standard petals show increased growth at their margins which may account for the overall differences in curvature between wild-type and hooded petals. The results of these analyses suggest that the hooded mutant of sweet pea is caused by a mutation in the CYC2 gene. CYC2 genes have been shown to play a role in establishing standard petal identity in the sweet pea and in a number of other legumes (Feng et al., 2006; Wang et al., 2008a).
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