Autophagy in plants: Physiological roles and post-translational regulation

In eukaryotes, autophagy helps maintain cellular homeostasis by degrading and recycling cytoplasmic materials via a tightly regulated pathway.Over the past few decades, significant progress has been made towards understanding the physiological functions and molecular regulation of autophagy in plant cells. Increasing evidence indicates that autophagy is essential for plant responses to several developmental and environmental cues, functioning in diverse processes such as senescence, male fertility, root meristem maintenance, responses to nutrient starvation,and biotic and abiotic stress. Recent studies have demonstrated that, similar to nonplant systems,the modulation of core proteins in the plant autophagy machinery by posttranslational modifications such as phosphorylation, ubiquitination,lipidation, S-sulfhydration, S-nitrosylation, and acetylation is widely involved in the initiation and progression of autophagy. Here, we provide an overview of the physiological roles and posttranslational regulation of autophagy in plants.

TRAF proteins as key regulators of plant development and stress responses

Tumor necrosis factor receptor-associated factor(TRAF)proteins are conserved in higher eukaryotes and play key roles in transducing cellular signals across different organelles.They are characterized by their C-terminal region(TRAF-C domain)containing seven to eight antiparallelβ-sheets,also known as the meprin and TRAF-C homology(MATH)domain.Over the past few decades,significant progress has been made toward understanding the diverse roles of TRAF proteins in mammals and plants.Compared to other eukaryotic species,the Arabidopsis thaliana and rice(Oryza sativa)genomes encode many more TRAF/MATH domaincontaining proteins;these plant proteins cluster into five classes:TRAF/MATH-only,MATH-BPM,MATH-UBP(ubiquitin protease),Seven in absentia(SINA),and MATH-Filament and MATHPEARLI-4 proteins,suggesting parallel evolution of TRAF proteins in plants.Increasing evidence now indicates that plant TRAF proteins form central signaling networks essential for multiple biological processes,such as vegetative and reproductive development,autophagosome formation,plant immunity,symbiosis,phytohormone signaling,and abiotic stress responses.Here,we summarize recent advances and highlight future prospects for understanding on the molecular mechanisms by which TRAF proteins act in plant development and stress responses.