The plastid-encoded protein Orf2971 is required for protein translocation and chloroplast quality control

Abstract

Photosynthesis and the biosynthesis of many important metabolites occur in chloroplasts. In these semi-autonomous organelles, the chloroplast genome encodes approximately 100 proteins. The remaining chloroplast proteins, close to 3000, are encoded by nuclear genes whose products are translated in the cytosol and imported into chloroplasts. However, there is still no consensus on the composition of the protein import machinery including its motor proteins and on how newly imported chloroplast proteins are refolded. In this study, we have examined the function of orf2971, the largest chloroplast gene of Chlamydomonas reinhardtii. Depletion of Orf2971 causes accumulation of protein precursors, partial proteolysis and aggregation of proteins, increased expression of chaperones and proteases, and autophagy. Orf2971 interacts with the TIC complex, catalyzes ATP hydrolysis and associates with chaperones and chaperonins. We propose that Orf2971 is intimately connected to the protein import machinery and plays an important role in chloroplast protein quality control.

Effects of high night temperature on soybean yield and compositions

“…It was found that among the DEGs for sucrose metabolism, 7 of 8 sucrose synthase genes and 2 Sucrose-phosphatase genes were down-regulated, including LOC100802045(Glyma.19G212800), LOC100788584 (Glyma.17G045800), LOC100788717 (Glyma.15G151000), LOC102662162 (Glyma.03G048351v4), LOC100806761 (Glyma.09G073600), LOC100793371 (Glyma.03G216300), SS, LOC100819730 (Glyma.15G182600), LOC100800397 (Glyma.10G086600), LOC100796915 (Glyma.20G070500), implying the sucrose synthesis of leaves was regulated at the transcriptional level by high night temperature at 7 DAT ( Figure 8 ). Among the photosynthetic carbon fixation-related genes, RBCS2 , which catalyzes the reaction of fixing CO 2 in photosynthesis and is an important enzyme related to chloroplast function ( Xing et al., 2022 ) is found up-regulated, which may be related to the rise of the photosynthesis at 7 DAT in this study.…”

“Omics” insights into plastid behavior toward improved carotenoid accumulation

“…Additionally, a Ycf2-FTSHi ATPase complex, acting as a motor for pulling preproteins across the inner envelope membrane, was identified as being associated with the TIC machinery ( Xing et al., 2022 ). Orf2971, the ortholog of Ycf2 and, is encoded by the largest gene in chloroplast genome of Chlamydomonas reinhardtii ( Chlamydomonas throughout) and directly associated with the protein import machinery to ensure the quality of proteins targeted to the chloroplast ( Xing et al., 2022 ).…”

“…Additionally, a Ycf2-FTSHi ATPase complex, acting as a motor for pulling preproteins across the inner envelope membrane, was identified as being associated with the TIC machinery ( Xing et al., 2022 ). Orf2971, the ortholog of Ycf2 and, is encoded by the largest gene in chloroplast genome of Chlamydomonas reinhardtii ( Chlamydomonas throughout) and directly associated with the protein import machinery to ensure the quality of proteins targeted to the chloroplast ( Xing et al., 2022 ). Particularly, Orf2971 interacts with CrTic214 (also called Orf1995 or Ycf1), a protein involved in chloroplast protein translocation, as well as with chaperones like Hsp70 and Cpn60, which direct protein folding or assembly ( Bonk et al., 1996 ; Bonk et al., 1997 ).…”

Understanding protein translocation across chloroplast membranes: Translocons and motor proteins

“…Because there is compelling in vivo and in vitro evidence that the ATPase chaperones Hsp93, cpHsp70, and Hsp90C play critical roles in protein import into chloroplasts, it is also necessary to reveal the possible mechanisms to reconcile the two models. Recently, Xing et al (2022) showed that Orf2971, which is a Chlamydomonas orthologue of Arabidopsis Ycf2, is involved in protein translocation into chloroplasts and exhibits ATPase activity. Moreover, Orf2971 was co‐purified with a TIC complex containing Tic20, Tic214, and an uncharacterized FtsH‐like protein, further confirming previous findings (Kikuchi et al, 2013; Kikuchi et al, 2018; Xing et al, 2022).…”

“…Recently, Xing et al (2022) showed that Orf2971, which is a Chlamydomonas orthologue of Arabidopsis Ycf2, is involved in protein translocation into chloroplasts and exhibits ATPase activity. Moreover, Orf2971 was co‐purified with a TIC complex containing Tic20, Tic214, and an uncharacterized FtsH‐like protein, further confirming previous findings (Kikuchi et al, 2013; Kikuchi et al, 2018; Xing et al, 2022).…”