The light-responsive transcription factor SlBBX20 improves saline-alkali resistance of Solanum lycopersicum by affecting photosynthetic capacity, antioxidant capacity, and osmotic adjustment

Abstract

The transcription factor BBX family is associated with plant responses to abiotic stress. Among the 31 SlBBXs genes in tomato, SlBBX20 is the most strongly induced by saline-alkali stress. However, the response mechanism of the SlBBX20 transcription factor under saline-alkali stress remains unclear. In this study, we investigated the effect of the SlBBX20 transcription factor on saline-alkali tolerance in tomato using wild-type (WT), SlBBX20 overexpression lines, SlBBX20-silenced materials (TRV2-SlBBX20) and their controls (TRV2-empty). Under normal conditions, overexpression of SlBBX20 increased tomato photosynthetic capacity (contents of chlorophyll a, chlorophyll b and carotenoids, net photosynthetic rate), leaf palisade and spongy tissue thickness, and total antioxidant capacity. In contrast, the photosynthetic capacity and total antioxidant capacity of SlBBX20 silenced material did not change significantly relative to the control. Under saline-alkali stress, overexpression of SlBBX20 significantly reduced the relative conductivity, malondialdehyde content, reactive oxygen species levels (O2•−, H2O2), and increased the relative water content, photosynthetic capacity, total antioxidant capacity, antioxidant enzyme activities (peroxidase, superoxide dismutase, and catalase) and proline content in tomato leaves. And silencing SlBBX20 showed the opposite trend. Furthermore, through transcriptome sequencing of WT and SlBBX20-OE lines grown in saline-alkali stress condition at 0 h and 12 h, three differentially expressed genes related to saline-alkali stress (SlP5CR, SlHsp21.6A, SlHsp26.2) were identified. Yeast one-hybrid and dual-luciferase assays confirmed that SlBBX20 might bind to the G-box cis-acting elements in the promoter regions of SlP5CR, SlHsp21.6A, and SlHsp26.2 genes, exerting transcriptional regulatory functions. In conclusion, overexpression of SlBBX20 enhances saline-alkali tolerance in tomatoes by sustaining leaf photosynthetic capacity, reducing ROS accumulation, and elevating antioxidant enzyme activity and proline content.