REGULATION OF PLASTID GENE-EXPRESSION IN RICE INVOLVES CALCIUM AND PROTEIN PHOSPHATASES KINASES FOR SIGNAL-TRANSDUCTION/

Spatial control of expression of plastid-encoded photosynthesis-relate d genes, psbA, psaA and rbcL, has been studied in rice (Oryza sativa L .) seedlings. Whereas roots accumulate negligible amount of mRNAs of t hese genes, shoots show high transcript levels. A gradient in expressi on 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 i n lower segment are significantly reduced on treatment with EGTA. The inhibitory effect of EGTA could be reversed by addition of calcium dur ing treatment. Nifedipine and verapamil-the calcium channel blockers-a lso decrease the levels of transcripts. Okadaic acid, the specific inh ibitor of protein phosphatases 1 and 2A (PPI and PP2A), and a general inhibitor of protein phosphatases, NaF, inhibit the steady-stale trans cript levels of psaA, pshA and rbcL significantly. Staurosporine, the protein kinase inhibitor, increases the steady-slate transcript levels of these genes. These results suggest the importance of calcium and p rotein phosphorylation in expression of genes during chloroplast bioge nesis. However, the inter-relationship of calcium effects and protein phosphorylation remains to be worked out. (C) 1998 Elsevier Science Ir eland Ltd. All rights reserved.