Translation and stability of proteins encoded by the plastid psbA and psbB genes are regulated by a nuclear gene during light-induced chloroplast development in barley.
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abstract
We have characterized a nuclear mutant of barley, viridis-115, lacking photosystem II (PSII) activity and compared it to wild-type seedlings during light-induced chloroplast development. Chloroplasts isolated from wild-type and viridis-115 seedlings illuminated for 1 h synthesized similar polypeptides and had similar protein composition. After 16 h of illumination, however, mutant plastids exhibited reduced ability to radiolabel D1, CP47, and several low Mr membrane polypeptides, and by 72 h, synthesis of these proteins was undetectable. Immunoblot analysis showed that plastids of dark-grown wild-type barley lacked several PSII proteins (D1, D2, CP47, and CP43) and that 16 h of illumination resulted in the accumulation of these polypeptides. In contrast, these polypeptides did not accumulate in illuminated viridis-115 seedlings, although mutant plastids accumulated two PSII proteins that participate in oxygen evolution, oxygen-evolving enhancers 1 and 3. Northern analysis showed that the levels of psbA and psbB mRNA in mutant plastids were equal to or greater than levels in wild-type plastids throughout the developmental period examined here. These results indicate that the nuclear mutation present in viridis-115 affects the translation and stability of the chloroplast-encoded D1 and CP47 polypeptides and that its influence is expressed after the onset of light-induced chloroplast development.
