A RING finger E3 ligase gene, Oryza sativa Delayed Seed Germination 1 (OsDSG1), controls seed germination and stress responses in rice
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Seed germination is an important character for plant growth and seed quality. We identified a rice mutant that was delayed in its germination. There, T-DNA was inserted into Oryza sativa Delayed Seed Germination 1 (OsDSG1), causing a recessive null mutation. Overexpression of the gene enhanced seed germination. OsDSG1 is most similar to Arabidopsis AIP2, an E3 ligase targeting ABI3.Yeast two-hybrid experiments showed that our OsDSG1 binds to OsABI3, indicating that OsDSG1 is a rice ortholog of AIP2. Self-ubiquitination assay indicated that bacterially expressed OsDSG1 protein has E3 ubiquitin ligase activity. Real-time PCR analysis revealed that OsDSG1 was expressed in leaves and roots, and strongly in developing seeds. In addition to the delayed-germination phenotype, mutant plants were shorter and had greater tolerance to high-salt and drought stresses. In the osdsg1 mutant, transcript levels of ABA signaling genes and ABA responsive genes were significantly increased. By contrast, expressions of OsGAMYB and its downstream genes that encode hydrolytic enzymes were markedly reduced. These observations support that OsDSG1 is a major regulator of ABA signaling in germinating seeds. Finally, we observed that the germination rates of various rice cultivars depended upon the transcript levels of OsDSG1 and other ABA-signaling genes.
KeywordsABA signaling Abiotic stresses E3 ligase Rice Seed germination
We thank Kyungsook An for plant transformation, Priscilla Licht for English editing, Gihwan Yi for providing the rice seeds and Jongjin Park, Sungryul Kim and Songlim Kim for helpful discussion. This work was supported, in part, by grants from the Crop Functional Genomic Center, the 21st Century Frontier Program (Grant CG1111); from the Biogreen 21 Program, Rural Development Administration (20070401-034-001-007-03-00); from the Korea Research Foundation Grant (MOEHRD, Basic Research Promotion Fund (KRF-2007-341-C00028); and from Kyoung Hee University (20100791).
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