Control of Seed Dispersal in Arabidopsis

University Of California-San Diego, La Jolla CA

Investigators

Abstract

Control of seed dispersal in Arabidopsis Fruit dehiscence, or pod shatter, is the result of a carefully orchestrated series of events late in fruit development resulting in seed dispersal. Programmed cell separation between dehiscence zone cells, presumably by secretion of pectin degrading enzymes, allows for separation of the fruit valves from the replum and release of the seeds. Lignification of specific cells within the fruit is also proposed to contribute to pod shatter, providing a "coiled spring" that actively pops the valves off of the replum. The PI has shown that the SHATTERPROOF1 and SHATTERPROOF2 (SHP1 and SHP2) MADS-box genes are required for differentiation of the dehiscence zone at the valve margin and for ignification of adjacent cells such that shp1 shp2 double mutants are indehiscent. The focus of this proposal is the cascade of gene activity beginning with SHP1 and SHP2 gene expression early in carpel development, and culminating in the secretion of pectin degrading enzymes from dehiscence zone cells and the subsequent detachment of the valves from the replum. Our research plan involves parallel genetic and molecular approaches toward unraveling this cascade. Genetic screens will be used to uncover additional loci involved in fruit dehiscence by identifying indehiscent mutants as well as suppressors of the shp1 shp2 mutant phenotype. Molecular approaches will use gene- and enhancer-trap lines that show valve margin expression domains. These markers will allow further haracterization of genes and mutants involved in the dehiscence process and provide a source of candidate genes that act downstream of SHP1 and SHP2. Use will also be made of DNA microarrays to identify additional genes regulated by SHP1 and SHP2. Mutant screens have already identified at least one additional locus required for fruit dehiscence, INDEHISCENT1 (IND1). The IND1 gene encodes a putative MYC-like basic helix loop helix transcription factor that requires SHP1 and SHP2 for expression. Based on our preliminary results we have developed a simple model for the interactions of genes during valve margin development. The use of the genes and mutants described in this proposal will allow us to directly test this model and to refine it as additional genes involved in valve margin development are revealed. The specific nature of the shp1 shp2 double mutant phenotype provides a unique system for understanding the cell differentiation process in plants as well as for examining the sharp boundary that forms between the distinct cell types that compose the fruit valves and the replum. In addition, investigating the processes which result in seed dispersal and lignification in Arabidopsis could lead to important contributions to crop improvement.