Transcription factor OsBZ8 directly activates multiple methylerythritol 4‐phosphate and the mevalonate pathway genes in rice seeds

The rice transcription factor OsBZ8 binds to the core sequence ACGT in a G‐box (CACGTG), hybrid G/C‐box (GACGTG) or abscisic acid response element (ACGTGGC) in the upstream promoter of its target genes. The expression of this transcription factor is largely restricted to seeds 25 days after pollination, coinciding with isoprenoid accumulation, suggesting it may be responsible for the coordinated regulation of the mevalonate (MVA) and the methylerythritol 4‐phosphate (MEP) pathway genes. We therefore screened the corresponding promoters for relevant cis ‐acting elements in 14 genes (three isoforms each of AACT , HMGS , HMGR and DXS and two of IPPI ) involved in the MVA/MEP pathways and found a G‐box or hybrid G/C‐box motif within the first 300 bp upstream of five genes ( OsAACT3 , OsHMGS1 , OsHMGR1 , OsDXS2 and OsIPPI1 ). The expression profile of all five genes in rice seeds matched that of OsBZ8 , with stronger expression in the embryo than the endosperm. The specific binding of OsBZ8 to three of the promoter elements was confirmed in yeast one‐hybrid assays, and reporter gene constructs provided direct evidence of transactivation in a representative gene. Our findings provide insight into the regulation of isoprenoid metabolism in rice and will facilitate the use of transcription factors in rice seeds to boost the production of target metabolites.