SlMYB86-SlXTH23 module positively assists ALA-alleviated growth inhibition in tomato seedlings under cold stress

Cold stress severely inhibits plant growth and development. Cell expansion is a key determinant of plant tissue growth. 5-Aminolevulinic acid (ALA) promotes cell expansion and growth of tomato seedlings under cold stress, accompanied by strong upregulation of the cell expansion enzyme: xyloglucan endotransglucosylase/hydrolase gene (SlXTH23). In this study, SlXTH23 was confirmed to positively regulate cold tolerance and growth in tomato, in association with cell wall metabolism and mesophyll cell expansion, as demonstrated using SlXTH23 transgenic lines. Transcriptome analysis identified SlMYB86, a transcription factor responsive to ALA and cold stress, as an upstream regulator of SlXTH23. Protein-DNA interaction assays demonstrated that SlMYB86 directly binds the SlXTH23 promoter and activates its expression. Functional validation using SlMYB86 transgenic lines showed regulatory patterns consistent with SlXTH23, confirming that SlMYB86 enhances cold tolerance and seedling growth. Collectively, these results demonstrate that the SlMYB86-SlXTH23 module assists ALA in alleviating cold-induced growth inhibition in tomato seedlings by reducing oxidative damage and promoting cell expansion.