Glycine betaine alleviates low temperature combined with low light stress in pepper (Capsicum annuum L.) by improving photosynthetic ability and regulating genes related m6A methylases

Low temperature combined with low light (LL) stress is a notable factor limiting the yield and economic viability of pepper cultivation in Northwest China. Glycine betaine (GB), an antioxidant and osmotic regulator, positively regulates abiotic stress in plants. However, few investigations have been conducted to determine whether GB modulates LL stress by involving changes in photosynthesis and m6A methylation. Herein, pepper seedlings were pre-treated with 20 mmol L-1 GB and 60 mu mol L-1 3-deazaneplanocin A hydrochloride (DAA) under LL stress of 10/5 degrees C and 100 mu mol m-2 s-1 to investigate the regulatory mechanism of GB-induced tolerance to LL. Results indicated that the pre-treatment with GB alleviated the growth inhibition and photoinhibition caused by LL stress. It considerably increased the photosynthetic capacity and chlorophyll content by protecting the photosynthetic electron-transport system, increasing the stomatal aperture and activity of enzymes in the Calvin cycle and upregulating the expression of the genes encoding chloroplast proteins. Additionally, GB reduced sugar content, regulated phytohormones, upregulated the expression levels of CaCBF1A, CaCBF1B, and CaF-BOX, and downregulated the expression levels of CaMTA, CaMTC, and CaFIP37 (m6A methylases). Conversely, it upregulated the expression levels of CaALKBH1 and CaALKBH6 (m6A demethylases). However, the addition of DAA worsened the damage caused by LL, yet when sprayed simultaneously with DAA and GB, this inhibition was reversed. These findings indicated that GB provided LL tolerance to pepper seedlings possibly by improving plant growth, enhancing photosynthetic properties, regulating sugar hormone metabolism, and mediating m6A methylase.