Alkaline Invertase 2 positively modulates cold adaptive of Camellia sinensis and enhances freezing and salt tolerance in transgenic Arabidopsis thaliana

Alkaline/neutral invertase (A/N-Inv) is a type of hydrolases that irreversibly hydrolyze sucrose into glucose and fructose, thus participating in the plant morphogenesis and stress responses. In tea plant, a putative A/N-Inv gene, CsINV2, mediated the abiotic stress responses of tea plant, but the detailed molecular mechanism has not been elucidated yet. In this study, CsINV2 was verified as an alkaline invertase that can split sucrose into glucose and fructose in vitro, which showed the optimal catalytic activity at 45 °C and pH 8 conditions. Besides, the high transcription of CsINV2 contributed to improving the cold adaptation of tea plant, while silencing of CsINV2 reduced cold adaptive of tea plant. Overexpression of CsINV2 improved freezing tolerance of transgenic Arabidopsis by improving A/N-Inv activity, glucose content, hexose/sucrose ratio, and also via a feedback regulation pathway. Meanwhile, overexpression of CsINV2 promoted gemination rate and root elongation of transgenic Arabidopsis under salt stress condition. Finally, a cold-induced transcription factor CsAHL17 was confirmed to interact with the promoter of CsINV2, silencing of CsAHL17 reduced the transcription of CsINV2 both under 25 °C and 4 °C conditions. In summary, it can draw a conclusion that CsINV2 regulates the cold resistance of tea plant by influencing the contents of different soluble sugar components under the regulation of CsAHL17. This study will further promote the understanding to the role of invertase in tea plants.