Ubiquitin-mediated degradation of SlPsbS regulates low night temperature tolerance in tomatoes

PsbS protein is essential for the rapid induction of non-photochemical quenching (NPQ) under low night temperatures (LNTs), but its stability is often affected by adverse environmental conditions. However, the regulatory mechanism for the stability of PsbS or chloroplast proteins remains to be fully characterized. We show that LNT decreases NPQ levels and SlPsbS protein abundance in tomato leaves. LNT-activated chloroplast vesicles (SlCVs) targeting the chloroplasts induce the formation of CV-containing vesicles (CCVs) containing SlPsbS, exported from the chloroplasts. Subsequently, SlCV and SlPsbS contact COP9 signalosome subunit 5A (SlCSN5A) in the cytosol and are ubiquitinated and degraded. Genetic evidence demonstrates that the overexpression of SlCV aggravates SlPsbS protein degradation, whereas silencing of SlCSN5 and SlCV delays LNT-induced NPQ reduction and SlPsbS protein turnover. This study reveals a ubiquitin-dependent degradation pathway of chloroplast proteins co-mediated by CV and CSN5A, thereby providing a basic reference for the regulation of chloroplast protein stability under stress conditions. [Display omitted] •Low night temperature stress promotes SlPsbS protein degradation•SlCSN5A ubiquitinates and degrades SlPsbS in the cytosol•SlCV regulates the stability of SlPsbS by promoting the contact between SlCSN5A and SlPsbS•SlCSN5A and SlCV negatively regulate plant stress resistance Lu et al. show that CSN5A is involved in chloroplast protein turnover, revealing a ubiquitin-dependent degradation pathway of intra-chloroplast proteins and CCVs jointly participated by CV and CSN5A.