| Summary: | 碩士 === 國立臺灣大學 === 植物科學研究所 === 105 === SUBMERGENCE1A-1 (SUB1A-1) is a member of the group-Vll ethylene response transcription factors (ERF-Vlls) which confers major flooding-tolerance to some rice cultivars, including FR13A and Pokkali. Encountering submergence stress, FR13A shows a “low oxygen quiescence syndrome (LOQS)” phenotype, including: 1) the transcription level of SUB1A-1 is highly up-regulated and 2) the growth of FR13A is retarded until the water subsided. Although possessing SUB1A-1 as well, Pokkali displays a contrasting flooding-tolerant phenotype. Pokkali has a much lower induction level of SUB1A-1 than that of FR13A and continues to grow under submergence. Microarray data showed that some GA2 OXIDASEs encoding enzymes that catalyze active GA to inactive forms were lowly induced in Pokkali than in FR13A during submergence. Additionally, a series of EXPANSINs, which are GA-responsive genes, had much higher induction levels in Pokkali. GC/MS analysis indicated that the level of GA4 is highly increased in Pokkali under submergence, but not changed in FR13A. Furthermore, GA3 and ethephon treatments revealed that high levels of GA inhibited the expression of SUB1A-1 under submergence, and ethylene could promote GA response in rice, respectively. Moreover, a number of genes were highly induced in Pokkali than in FR13A under submergence, including HEMOGLOBIN, ACYL-ACP DESATURASE, CLC7 and HAK1, which may contribute to submergence tolerance of Pokkali. Based on these results, we hypothesized that in Pokkali ethylene triggers higher GA accumulation, which represses SUB1A-1 induction at lower levels. HEMOGLOBIN, ACYL-ACP DESATURASE, CLC7 and HAK1, which were highly induced in Pokkali than in FR13A under submergence, might participate in submergence tolerance of Pokkali.
Furthermore, prior studies showed that ERF66 and ERF67, members of ERF-Vlls, might be regulated by SUB1A-1. Through trans-activation assays, we proved that SUB1A-1 not only positively regulated the transcription of ERF66 and ERF67, but also activated itself at the transcription level. It is possible that SUB1A-1 binds other cis-element at the SUB1A-1’s promoter other than GCC box, which conferred flooding tolerance to rice by activating itself at the transcription level and enhanced the transcription of downstream targets, including ERF66 and ERF67.
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