Plastid promoter utilization in a rice embryogenic cell culture.

Plastid promoter utilization was characterized in rice by mapping transcript 5'-ends in samples derived from leaves and cultured embryogenic cells. We have found that rbcL, atpB and the rRNA operon are transcribed by the plastid-encoded plastid RNA polymerase (PEP), while clpP is transcribed by the nucleus-encoded plastid RNA polymerase (NEP) in both chloroplasts and the non-green plastids of embryogenic cultured cells. This finding is in contrast to reports on BY2 tobacco, in which NEP promoter activity in cultured cells was enhanced relative to leaves, facilitating identification of NEP promoters which are undetectable in chloroplasts. Therefore, it appears that activation of plastid NEP promoters in rice is not essential for adaptation to cell culture.