Abstract
Momilactones and phytocassanes are major diterpenoid phytoalexins, which are produced in elicitor-treated rice cells. We recently showed that biosynthetic genes for momilactones (OsCPS4, OsKSL4, CYP99A2, CYP99A3, OsMAS) are clustered on rice chromosome 4, and that those for phytocassanes (OsCPS2, OsKSL7, CYP71Z7) are clustered on rice chromosome 2. Moreover, we reported that an elicitor-inducible bZIP transcription factor, OsTGAP1, is essential for momilactone biosynthesis and regulates the expression of the five genes in the cluster. Here we report OsTGAP1 is involved also in the elicitor-inducible expression of methylerythritol phosphate (MEP) pathway genes (OsDXS3, OsDXR, OsCMS) and phytocassane biosynthetic genes (OsCPS2, OsKSL7). Inductive expression of OsCPS2 and OsKSL7 after elicitation seen in wild-type cells was weakened in ostgap1 mutant, although phytocassane accumulation still occurred. On the other hand, OsTGAP1 over-expressing lines exhibited enhanced expression of OsCPS2 and OsKSL7 and hyper-accumulation of phytocassanes in response to the elicitor. We also found that the elicitor-induced expression of OsDXS3, OsDXR and OsCMS, was significantly suppressed in the ostgap1 mutant and that OsTGAP1 over-expression exhibited enhanced expression of OsDXS3, OsDXR and OsCMS. These results indicate that OsTGAP1 functions as a key regulator of the coordinated transcription of genes involved in the elicitor-induced diterpenoid phytoalexin production in rice.