Plastid Genes Encoding the Transcription/Translation Apparatus Are Differentially Transcribed Early in Barley (Hordeum vulgare) Chloroplast Development (Evidence for Selective Stabilization of psbA mRNA)

Chloroplast genomes encode rRNAs, tRNAs, and proteins involved in transcription, translation, and photosynthesis. The expression of 15 plastid genes representing each of these functions was quantitated during chloroplast development in barley (Hordeum vulgare). The transcription of all plastid genes increased during the initial phase of chloroplast development and then declined during chloroplast maturation. RNAs corresponding to rpoB- rpoC1-rpoC2, which encode subunits of a plastid RNA polymerase, and rps16, which encodes a ribosomal protein, reached maximal abundance early in chloroplast development prior to genes encoding subunits of the photosynthetic apparatus (rbcL, atpB, psaA, petB). Transcription of rpoB as well as 16S rRNA, trnfM-trnG, and trnK was high early in chloroplast development and declined 10-fold relative to rbcL transcription during chloroplast maturation. RNA hybridizing to psbA and psbD, genes encoding reaction center proteins of photosystem II, was differentially maintained in mature chloroplasts of illuminated barley. Differential accumulation of psbD mRNA relative to rbcL mRNA was due to light-stimulated transcription of psbD. In contrast, enhanced levels of psbA mRNA in mature chloroplasts were due primarily to selective stabilization of the psbA mRNA. These data document dynamic modulation of plastid gene transcription and mRNA stability during barley chloroplast development.