Regulation of abscisic acid signaling by the ethylene response pathway in arabidopsis

Although abscisic acid (ABA) is involved in a variety of plant growth and d evelopmental processes, few genes that actually regulate the transduction o f the ABA signal into a cellular response have been identified. In an attem pt to determine negative regulators of ABA signaling, we identified mutants , designated enhanced response to ABA3 (era3), that increased the sensitivi ty of the seed to ABA. Biochemical and molecular analyses demonstrated that era3 mutants over-accumulate ABA, suggesting that era3 is a negative regul ator of ABA synthesis. Subsequent genetic analysis of era3 alleles, however , showed that these are new alleles at the ETHYLENE INSENSITIVE2 locus. Oth er mutants defective in their response to ethylene also showed altered ABA sensitivity; from these results, we conclude that ethylene appears to be a negative regulator of ABA action during germination. In contrast, the ethyl ene response pathway positively regulates some aspects of ABA action that i nvolve root growth in the absence of ethylene. We discuss the response of p lants to ethylene and ABA in the context of how these two hormones could in fluence the same growth responses.