ABA Signaling Networks Controlling the Transition from Embryogenesis to Seedling Growth

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Production of healthy nutrient-rich seeds that delay their germination until field conditions are optimal for survival is controlled by integration of information from internal and environmental signals. One of the major internal regulators of both seed maturation and germination is the hormone abscisic acid (ABA). Genetic studies have identified genes that are required for normal seed maturation and ABA sensitivity of germination and seedling growth. Many of these genes encode transcription factors, i.e. proteins that bind to DNA and regulate expression of many other genes. Two of these factors, ABI4 and ABI5, each appear to regulate less than 10% of all ABA-regulated genes but confer hypersensitivity to ABA and other stresses when overproduced, suggesting that the relatively small group of genes they regulate are a core component of response to these signals. Comparison of ABA-induced genes in lines that either lack or overproduce these factors identified 16 potential regulatory loci that appear to be directly regulated by ABI4 or ABI5, in addition to many genes thought to mediate stress tolerance and a large number of genes of unknown function. The experiments outlined in this proposal will use genetic and molecular studies to determine which of these newly identified regulators are important for seed maturation and specific stress responses. One intriguing possibility suggested by the preliminary results is that ABA signaling via these ABI loci may enhance responses to other signals by increasing expression of appropriate receptors. Broader impacts of these studies include training of postdocs, and graduate and undergraduate students. Finally, these results may lead to strategies for manipulation of seed nutritional, germination or storage qualities to prevent millions of dollars in crop losses.