Overexpression of an autophagy-related gene DiATG3 from Davidia involucrata improves plant thermotolerance by enhancing the accumulation of polyamines and regulating genes in calcium and MAPK signaling pathways

Autophagy, a conserved eukaryotic mechanism for degrading intracellular constituents, plays prominent roles in plant abiotic stress tolerance. This study aimed to isolate an autophagy-related gene DiATG3 from a cool-adapted endangered plant species, dove tree (Davidia involucrata Baill.), and to investigate the physiological functions and regulatory mechanisms of DiATG3 for improving heat tolerance. DiATG3 was found to mainly localize to cytoplasm and possess the N-terminal domain, the catalytic domain with the HPC motif, and the C-terminal domain with the FLKF motif. Elevated transcript level of DiATG3 was detected in D. involucrata treated with heat stress. The constitutive overexpression of DiATG3 in Arabidopsis led to elevated levels of autophagy and conferred tolerance under heat stress. Furthermore, this thermotolerant phenotype was associated with improved photosynthetic capacity, higher antioxidant enzyme activities, and increased accumulation of polyamines. Transcriptome analysis suggest that activated calcium signaling and mitogen-activated protein kinase (MAPK) cascade may act as a central hub necessary for DiATG3-mediated heat tolerance. In addition, DiATG3 overexpression resulted in up-regulated expression of stress-related genes including heat shock factor A3 (AtHSFA3), dehydration-responsive element-binding protein 2C (AtDREB2C), AtWRKY26, and AtWRKY33 after heat treatment. Our study could yield insights into the engagement of plant autophagy during abiotic stress responses and contribute to breeding and engineering thermotolerant endangered plant species.