ClpC2 plays an essential role in shoot and root growth in Arabidopsis thaliana

Chaperones are essential for Clp protease that governs protein quality control in chloroplast. However, it remains poorly understood whether and how individual ClpC proteins play distinct roles in plant growth and development. In this study, we isolated a new allele of clpc2, designated sot11, from genetic suppressor screening of the thf1 leaf variegation phenotype. DNA sequencing combined with protein structural modeling revealed that the sot11 mutation causes a substitution of Thr to Ile at position 868 located within a loop region of ClpC2, leading to partial loss-of-function of ClpC2. Genetic and phenotypic assays demonstrated that sot11 suppresses not only thf1-mediated but also var2/ftsh2-mediated leaf variegation. Notably, sot11 fails to restore high-light hypersensitivity and the reduced FtsH protease levels observed in thf1. In addition, CRISPR-Cas9-generated complete knockout mutants of clpc2 exhibit severe growth retardation, markedly shortened roots, and pronounced anthocyanin accumulation, compared to the wild type (WT) plants, revealing a dosage-dependent relationship between ClpC2 activity and plant fitness. Taken together, these findings suggest that ClpC2 plays an important role in both shoot and root growth, opening a new avenue for investigating the organ-specific molecular mechanisms underlying ClpC2 function.