Abstract
The diterpene cyclase gene OsKS4 is involved in the biosynthesis of momilactones, major phytoalexins in rice. In suspension-cultured rice cells, transcriptional expression of OsKS4 and production of momilactones were strongly induced by treatment with a chitin elicitor. We identified a TGACG-sequence as an elicitor-responsive cis-element in the promoter of OsKS4 using reporter gene assays. This strongly suggests that a bZIP transcription factor regulates expression of OsKS4. We identified two elicitor-induced bZIP transcription factor genes OsTGA1 and OsbZIP21 using microarray followed by real-time PCR analysis, and found OsKS4 expression was robustly suppressed in a tos17 insertion mutant for OsTGA1 gene. In this mutant, production of momilactones was also suppressed. Additionaly, gel-mobility shift assays indicated that GST-OsTGA1 could specifically recognize and interact with the elicitor-responsive cis-element in the promoter of OsKS4. These results suggest that OsTGA1 participates in regulation of the elicitor-induced production of momilactones through controlling of OsKS4 expression.
