The Chloroplast Ribonucleoprotein CP33B Quantitatively Binds the psbA mRNA

Characterization of the preferred cation cofactors of chloroplast protein kinases in Arabidopsis thaliana

Chloroplasts sense a variety of stimuli triggering several acclimation responses. One prominent response is the mechanism of state transitions, which enables rapid adaption to changes in illumination. Here, we investigated the link between divalent cations (calcium, magnesium, and manganese) and protein kinase activity in Arabidopsis chloroplasts. Our results show that manganese ions are the strongest activator of kinase activity in chloroplasts followed by magnesium ions, whereas calcium ions are not able to induce kinase activity. Additionally, the phosphorylation of specific protein bands is strongly reduced in chloroplasts of a cmt1 mutant, which is impaired in manganese import into chloroplasts, as compared to the wild-type. These findings provide insights for the future characterization of chloroplast protein kinase activity and potential target proteins.

Identification and expression analysis of chloroplast ribonucleoproteins (cpRNPs) in Arabidopsis and rice

Chloroplast ribonucleoproteins (cpRNPs) are implicated in splicing, editing, and stability control of chloroplast RNAs as well as in regulating development and stress tolerance. To facilitate a comprehensive understanding of their functions, we carried out a genome-wide identification, curation, and phylogenetic analysis of cpRNP genes in Oryza sativa (rice) and Arabidopsis thaliana (Arabidopsis). Ten cpRNP genes were identified in each of Arabidopsis and rice genomes based on the presence of two RRM (RNA-recognition motif) domains and an N-terminal chloroplast targeting signal peptide in the predicted proteins. These proteins are localized to chloroplasts. Gene expression analysis revealed that cpRNP genes have differential tissue expression patterns and some cpRNP genes are induced by abiotic stresses such as cold, heat, and drought. Taken together, our study provides a comprehensive annotation of the cpRNP gene family and their expression patterns in Arabidopsis and rice which will facilitate further studies on their roles in plant growth and stress responses.