SlWRKY42 positively promotes proline accumulation by regulating SlP5CS1 to enhance tomato salt stress tolerance

1. SlWRKY42 positively regulates salt tolerance in tomato. 2. SlWRKY42 positively regulates transcription of SlP5CS1 and promotes the accumulation of proline under salt stress. 3. Exogenous proline alleviated the damage of slwrky42 mutants under salt stress. Tomato ( Solanum lycopersicum L.) is an important vegetable crop worldwide. Throughout its growth cycle, tomato is susceptible to various abiotic stresses. Among these stresses, salt stress is one of the most detrimental abiotic factors to plant growth and development. In this study, we identified a WRKY transcription factor, SlWRKY42 , which is induced by salt stress. We then characterized the function of SlWRKY42 in transgenic materials under salt stress and found that SlWRKY42 positively regulates salt tolerance in tomato. Transcriptome sequencing analysis revealed that genes involved in proline biosynthesis were significantly enriched in SlWRKY42 -overexpressing ( SlWRKY42 OE) plants. The proline biosynthesis genes ( SlP5CS1 and SlP5CS2 ) and proline contents were significantly upregulated in SlWRKY42 OE lines. We discovered that the promoter of the proline biosynthesis gene SlP5CS1 contains a W-box element. Further yeast one-hybrid (Y1H), luciferase, electrophoretic mobility shift assay (EMSA), and chromatin immunoprecipitation quantitative polymerase chain reaction (ChIP-qPCR) assays verified that SlWRKY42 could specifically bind to the W-box element in the promoter of SlP5CS1 and activate its expression, thereby promoting proline biosynthesis. In summary, SlWRKY42 enhances salt tolerance in tomato by regulating the expression of SlP5CS1 , thereby elucidating the molecular mechanism by which the SlWRKY42 transcription factor controls salt tolerance in tomato.