Stress granules as transient reservoirs for autophagy proteins: a key mechanism for plant recovery from heat stress.

Abstract

Stress granules (SGs) are transient, non-membrane-bound cytoplasmic condensates that form in response to environmental stresses, serving as protective reservoirs for mRNAs and proteins. In plants, SGs play a crucial role in stress adaptation, but their relationship with macroautophagy/autophagy, a key process for degrading damaged organelles and misfolded proteins, remains poorly understood. In a recent study, we revealed that key autophagy proteins, including components of the ATG1-ATG13 kinase complex, the class III phosphatidylinositol 3-kinase (PtdIns3K) complex, and the ATG8-PE system, translocate to SGs during heat stress (HS) in Arabidopsis thaliana. Using biochemical, cell biological and genetic approaches, we demonstrated that ATG proteins accumulate on HS-induced SGs and are released to the cytosol upon SG disassembly during the post-HS recovery stage. This process facilitates rapid autophagy activation. Notably, a SG-deficient mutant (ubp1abc) exhibits delayed autophagy activation and impaired clearance of ubiquitinated protein aggregates, highlighting the importance of SGs in regulating autophagy. Our findings uncover a novel mechanism by which SGs sequester autophagy proteins during stress, ensuring their rapid availability for stress recovery, and provide new insights into the interplay between SGs and autophagy in plant stress responses.Abbreviation: ATG, autophagy related; HS, heat stress; PtdIns3K, phosphatidylinositol 3-kinase; RBP47B, RNA-binding protein 47B; SG, stress granule; UBP1, ubiquitin-specific protease 1.