An RNA-chaperone-like Protein in Chloroplasts

Jiang et al. isolated a plastid-localized RNA-chaperone-like protein and investigated its function. Plant Cell

 By Jingjing Jiang, Xin Chai, Nikolay Manavski, and Wei Chi

 Background: RNA folding, which underlies the formation of RNA structure, is important for the functions and regulation of RNAs in all living organisms. RNA chaperone proteins have evolved to assist in the (re)folding of RNA molecules. As a rather independent organelle, the plant chloroplast generates RNA molecules using its own gene expression system. However, our knowledge of RNA chaperone(s) inside chloroplasts is poorly understood.

 Question: We set out to determine whether plant chloroplasts contain RNA chaperone protein(s), and if so, their roles in RNA metabolism in chloroplasts.

Findings: We isolated an RNA chaperone-like protein localized to the chloroplasts of Arabidopsis using a genetic method. Like many RNA chaperones, BSF (petB/petD Stabilizing Factor) shows nucleic-acid-melting activity, and its absence induces structural changes in RNA. Using various biochemical approaches, we found that BSF is associated with several chloroplast mRNAs. Further study showed that BSF indeed unfolds the structures of these RNAs to facilitate the binding of CRP1 (CHLOROPLAST RNA PROCESSING1), another important factor in chloroplast gene expression. In addition, we found that the RNA-binding protein PrfB3 can promote the RNA binding ability of BSF, suggesting that the function of BSF also requires the assistance of other RNA-binding proteins. Overall, our study uncovered an RNA-chaperon-like factor in plant chloroplasts and revealed its important role in chloroplast gene expression.

 Next steps: Our findings raise multiple questions. Does BSF support the functions of other RNA-binding factors as an RNA chaperone-like protein? How does PrfB3 promote the RNA-binding ability of BSF? It would also be highly interesting to study the involvement of the relationship between CRP1 and PrfB3 in chloroplast gene expression.

Jingjing Jiang, Xin Chai, Nikolay Manavski, Rosalind Williams- Carrier , Baoye He, Andreas Brachmann, Daili Ji, Min Ouyang, Yini Liu, Alice Barkan, Jörg Meurer, Lixin Zhang and Wei Chi (2019). An RNA-chaperone-like protein plays critical roles in chloroplast mRNA stability and translation in Arabidopsis and maize. Plant Cell 31: xx.

Key words: RNA, RNA folding, chaperone, chloroplast, plastid