Pentatricopeptide repeat (PPR) proteins,containing tandem repeats of degenerate 35 amino acid motifs,are important for post-transcriptional chloroplast gene expression. In this study,we report the characterization of a pigment-deficient mutant 1 (pdm1) in Arabidopsis,which displays the albino phenotype. PDM1 contains 5 PPR motifs followed by a PLS domain. The levels of plastid-encoded polymerase-dependent chloroplast genes were reduced dramatically,whereas those of nucleus-encoded polymerase-dependent chloroplast genes increased in the mutant. In addition,the pattern of rpoA pre-mRNA was altered and the rpoA transcript was absent in pdm1. Thus,these results suggest that PDM1 is required for processing of rpoA pre-mRNA in Arabidop-sis.
Deg1,a thylakoid lumen-localized protease,retains both chaperone and protease activities.The in vivo function of Deg1 has been shown to be involved not only in PSII assembly but also in the degradation of PSII reaction center protein D1.Here we used the transgenic plants with reduced Deg1 to examine whether the lumen-localized proteins are also the substrates of Deg1 in vivo.Our results showed that the transgenic plants accumulated degradation products of the PsbO protein while the levels of full-length PsbO were not affected.The PsbO degradation products could be efficiently degraded by the recombinant Deg1.These results suggest that Deg1 is involved in the degradation of the PsbO degradation fragments,but not in the initial cleavage event itself.
