Functional analysis of novel transcription factors of Arabidopsis thaliana involved in the regulation of nutrient storage.

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1.Targets and function of ASML1/WRI1 involved in seed oil accumulation.An AP2-type transcriptional activator ASML1/WRI1 of Arabidopsis thaliana is expressed during seed maturation phase. We found that many genes involved in fatty acid synthesis in plastids are direct targets of ASML1/WRI1 and identified consensus DNA binding sequence. While ASML1/WRI1 fascillitates flow of carbon to oil synthesis during seed development, two other ASML1/WRI1 subfamily members are likely to regulate fatty acid synthesis in vegetative tissues2.Function of ASML2 with the CCT domainAlthough we found that CCT domain of ASML2 interacts with B3 domain of ABI3 that controls seed maturation, gene for ASML2 was expressed only weakly during seed maturation phase. Instead, ASML2-Like I that also activates sugar-inducible gene and interacts with ABI3 and HSI2 is expressed during seed maturation phase. We identified a mutant with disruption of ASML2-L1 gene.3. Repression of seed maturation program by HSI2 and HSL1HSI2 and HSL1 are novel B3-EAR transcriptional repressors that repress sugar-inducible gene expression. Seedlings with knockouts of both genes (KK mutant) express embryonic and seed maturation genes and stop growth 7 days after germination, suggesting that HSI2/HSL1 are essential for the repression of seed maturation program and transition to vegetative growth after germination. It was suggested that the C-terminal EAR repression motif of HSI2 is not essential for this function. We identified candidates of targets of HSL1 by using hsi2 knockout plants with DEX-inducible RNAi for HSL1 which enabled us to induce KK mutant phenotype by treatment with DEX.