Degradation of Fatty Acid Export Protein1 by Rhomboid-Like Protease11 Contributes to Cold Tolerance in Arabidopsis

Plants need to adapt to different stresses to optimize growth under unfavorable conditions. The abundance of the chloroplast envelope located Fatty Acid Export Protein1 (FAX1) decreases after the onset of low temperatures. However, it was unclear how FAX1 degradation occurs and whether altered FAX1 abundance contributes to cold tolerance in plants. The rapid cold-induced increase in rhomboid-like protease11 (RBL11) transcript, the physical interaction of RBL11 with FAX1, the specific FAX1 degradation after RBL11 expression, and the absence of cold-induced FAX1 degradation in rbl11 loss-of-function mutants suggest that this enzyme is responsible for FAX1 degradation. Proteomic analyses showed that rbl11 mutants have higher levels of FAX1 and other proteins involved in membrane lipid homeostasis, suggesting that RBL11 is a key element in the remodeling of membrane properties during cold. Consequently, in the cold, rbl11 mutants show a shift in lipid biosynthesis towards the eukaryotic pathway, which coincides with impaired cold tolerance. To demonstrate that cold sensitivity is due to increased FAX1 levels, FAX1 overexpressors were analyzed. rbl11 and FAX1 overexpressor mutants show superimposable phenotypic defects upon exposure to cold temperatures. Our results show that the cold-induced degradation of FAX1 by RBL11 is critical for Arabidopsis to survive cold and freezing periods. ### Competing Interest Statement The authors have declared no competing interest.