Functional characterization of a chloroplast-targeted RNA-binding protein CRP1 in Arabidopsis thaliana under abiotic stress conditions

Although recent analysis of proteomes in specific cellular organelles of plants has demonstrated that more than 2,000 nuclear-encoded proteins are targeted to the chloroplast, the physiological functions of a majority of the proteins in chloroplasts are largely unknown. Here, we investigated the functional role of a chloroplast-targeted RNA-binding protein in Arabidopsis thaliana (At4g20030), designated CRP1 (for chloroplast-targeted a(1)NA-binding protein1), during seed germination and seedling growth under different light environments and various stress conditions. Confocal analysis of subcellular localization of CRP1-GFP fusion protein revealed that CRP1 protein is localized to the chloroplast. The T-DNA insertion loss-offunction crp1 mutant displayed poorer seedling growth than the wild-type plants under UV and high temperature stress conditions. Germination of crp1 mutant seeds was delayed compared with that of the wild-type seeds under cold or salt stress but not under dehydration stress conditions. The transgenic Arabidopsis plants that overexpress CRP1 showed better root and hypocotyl growth than wild type under heat stress conditions. Taken together, these results suggest that the chloroplast-targeted CRP1 plays a role in seed germination and seedling growth under UV, heat, cold, or salt stress but not under dehydration stress conditions.