Cloning and characterization of three cDNAs encoding chloroplast RNA-binding proteins from barley (Hordeum vulgare L.): differential regulation of expression by light and plastid development.

Three cDNAs encoding chloroplast RNA-binding proteins (RNBPs) were identified in a screen of barley albostrians mutant expression libraries, and their binding and expression characteristics were determined. Two of these proteins, designated cp31AHv and cp31BHv, are closely related to group II, whereas the third, cp33Hv, is more similar to group III of the nuclear-encoded chloroplast RNBPs of dicot plants. Analysis of RNA from sections of primary leaves by Northern hybridization showed that the expression of these genes correlates with the stage of leaf development. The steady state transcript levels of the two genes encoding cp31BHv and cp33Hv, but not of the gene for cp31AHv, were positively affected by light. Moreover, a plastid factor is required for activation of cp31AHv transcription as revealed by the low level of cp31AHv mRNA in white leaves of the albostrians mutant and of seedlings treated with Norflurazon. Therefore, we propose the existence of a light-independent plastid-derived signal chain that regulates the expression of cp31AHv.