TrSAMDC1 regulates heat-induced leaf senescence associated with changes in polyamine levels, chlorophyll metabolism, and lipids reprogramming

SAMDC1 encodes an S-adenosylmethionine decarboxylase which is a rate limiting enzyme for biosyntheses of spermidine (Spd) and spermine (Spm), but its function was not well documented in plants under heat stress. The objective of study was to reveal potential roles of TrSAMDC1 cloned from white clover (Trifolium repens) in mediating heat tolerance associated with changes in accumulations of endogenous Spd and Spm, antioxidant defense, chlorophyll (Chl) metabolism, and lipids reprogramming. In response to heat stress, TrSAMDC1-transgenic Arabidopsis thaliana (OE) delayed leaf senescence as compared to wild type (WT). Maintenance of higher endogenous Spd and Spm levels in the OE not only helped to improve Chl biosynthesis and decrease Chl catabolism for photosynthetic performance, but also enhanced antioxidant defense to reduce membrane lipid peroxidation. For lipidomics analysis, TrSAMDC1 overexpression significantly improved accumulations of phospholipids (PS, PC, PE, and PG), glycoglycerolipids (SQDG, DGMG, DGDG, and MGDG), and sphingolipids (Her1Cer and her3Cer) as well as the ratio of PC to PE, which played positive roles in maintenance of membrane system structure, functionality, and stability under heat stress. In addition, significant increases in endogenous Spd and Spm contents in white clover via exogenous application of Spm could also effectively mitigate heatinduced leaf senescence associated with enhanced antioxidant defense, reduced Chl catabolism, and improved Chl anabolism. Current findings indicated that the TrSAMDC1 acted as a negative regulator in leaf senescence under heat stress.