Control of Seed Dispersal in Arabidopsis

拟南芥种子传播的控制果实裂开，或角果破碎，是果实发育后期一系列精心策划的事件导致种子传播的结果。裂隙带细胞之间的程序性细胞分离，可能是通过分泌果胶降解酶，使果瓣与果核分离，并释放种子。果实内特定细胞的木质化也被认为是导致豆荚破碎的原因，提供了一个“卷曲的弹簧”，积极地将阀门从复叶上弹出。PI表明，SHATTERPROOF1和SHATTERPROOF2(SHP1和SHP2)MADS-box基因是瓣膜边缘裂区分化和相邻细胞木质化所必需的，从而使SHP1 Shp2双突变体不开裂。这一建议的重点是基因活性的级联，从心皮发育早期的SHP1和SHP2基因表达开始，最终导致裂隙区细胞分泌果胶降解酶，随后瓣膜从复膜上脱落。我们的研究计划涉及并行的遗传和分子方法来解开这一级联。遗传筛选将被用来通过鉴定SHP1 Shp2突变表型的不裂突变和抑制子来揭示与果实开裂有关的其他基因座。分子方法将使用显示瓣膜边缘表达结构域的基因和增强子陷阱线。这些标记将允许进一步表征参与裂开过程的基因和突变体，并提供作用于SHP1和SHP2下游的候选基因来源。还将使用DNA微阵列来识别受SHP1和SHP2调控的其他基因。突变筛选已经确定了至少一个额外的水果裂开所需的基因座，INDEHISCENT1(IND1)。IND1基因编码一个可能的MYC样碱性螺旋环状螺旋转录因子，需要SHP1和SHP2才能表达。基于我们的初步结果，我们开发了一个简单的模型，用于研究瓣膜边缘发育过程中基因之间的相互作用。使用本提案中描述的基因和突变体将使我们能够直接测试这一模型，并随着与瓣膜边缘发育有关的其他基因的揭示而对其进行改进。SHP1 Shp2双突变表型的特殊性为理解植物的细胞分化过程以及检查组成果瓣和复制质的不同细胞类型之间形成的尖锐边界提供了一个独特的系统。此外，研究导致拟南芥种子传播和木质化的过程可能会对作物改良做出重要贡献。

Control of seed dispersal in ArabidopsisFruit 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.