ARS | Publication request: Control of Dissected Leaf Morphology by a Cys(2)His(2) Zinc Finger Transcription Factor in the Model Legume Medicago Truncatula

Submitted to: Proceedings of the National Academy of Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 30, 2010
Publication Date: June 8, 2010
Citation: Chen, J., Yu, J., Ge, L., Wang, H., Berbel, A., Liu, Y., Chen, Y., Li, G., Tadege, M., Wen, J., Cosson, V., Mysore, K.S., Ratet, P., Madueno, F., Bai, G., Chen, R. 2010. Control of Dissected Leaf Morphology by a Cys(2)His(2) Zinc Finger Transcription Factor in the Model Legume Medicago Truncatula. Proceedings of the National Academy of Sciences. 107:10754-10759

Interpretive Summary: As the primary organ for photosynthetic carbon fixation, plant leaves play an important role in plant growth, biomass production and survival in the environment. Plant leaves show great differences in their morphology, which contribute to the diversity of plant types in the natural environment. How different leaf morphologies are determined is not yet understood. Medicago truncatula is a legume plant species and its leaf consists of three blades (leaflets). We demonstrate that development of the leaves with three leaflets is determined by a gene called PALM1 that produces a transcription factor. A plant with nonfunctional PALM1 develops dissected leaves with five leaflets. This basic research could eventually lead to forage crops with higher leaf to stem ratios and thus higher feed value.

Technical Abstract: Different plants may have different leaf types. Diversity in leaf types contributes to a large degree of plant diversity in the natural environment. How different leaf morphology is determined is not yet understood. The leguminous plant Medicago truncatula exhibits dissected leaves with three leaflets at the tip. We show that development of the trifoliate leaves is determined by the Cys(2)His(2) zinc finger transcription factor PALM1. Loss-of-function mutants of PALM1 develop dissected leaves with five leaflets clustered at the tip. We demonstrate that PALM1 binds a specific promoter sequence and down-regulates the expression of the Medicago truncatula LEAFY/ UNIFOLIATA orthologue SINGLE LEAFLET1 (SGL1), encoding an indeterminacy factor necessary for leaflet initiation. Our data indicate that SGL1 is required for leaflet proliferation in the palm1 mutant. Interestingly, ectopic expression of PALM1 effectively suppresses the lobed leaf phenotype from overexpression of a class 1 KNOTTED1-like homeobox protein in Arabidopsis plants. Taken together, our results show that PALM1 acts as a determinacy factor, regulates the spatial-temporal expression of SGL1 during leaf morphogenesis, and together with the LEAFY/UNIFOLIATA orthologue plays an important role in orchestrating the compound leaf morphology in Medicago truncatula.