Regulation of plastid gene expression in rice involves calcium and protein phosphatases/kinases for signal transduction

Abstract

Spatial control of expression of plastid-encoded photosynthesis-related genes, psbA, psaA and rbcL, has been studied in rice ( Oryza sativa L.) seedlings. Whereas roots accumulate negligible amount of mRNAs of these genes, shoots show high transcript levels. A gradient in expression of these genes is seen even in lower, middle and upper segments of leaf sheath, with lower segment showing the least amount of mRNA—being nearer to the meristematic zone. The steady-state transcript levels in lower segment are significantly reduced on treatment with EGTA. The inhibitory effect of EGTA could be reversed by addition of calcium during treatment. Nifedipine and verapamil—the calcium channel blockers—also decrease the levels of transcripts. Okadaic acid, the specific inhibitor of protein phosphatases 1 and 2A (PPI and PP2A), and a general inhibitor of protein phosphatases, NaF, inhibit the steady-state transcript levels of psaA, psbA and rbcL significantly. Staurosporine, the protein kinase inhibitor, increases the steady-state transcript levels of these genes. These results suggest the importance of calcium and protein phosphorylation in expression of genes during chloroplast biogenesis. However, the inter-relationship of calcium effects and protein phosphorylation remains to be worked out.