Mitigating Response of <i>SlCSE06</i> Induced by 2-Ethylfuran to <i>Botrytis cinerea</i> Infection

Tomato (<i>Solanum lycopersicum</i> L.) is a major economic vegetable crop globally, yet it is prone to gray mold disease caused by <i>Botrytis cinerea</i> infection during cultivation. Caffeoyl shikimate esterase (CSE) is a crucial component of the lignin biosynthesis pathway, which significantly contributes to plant stress resistance. Therefore, investigating the expression patterns of <i>SlCSE</i> after <i>Botrytis cinerea</i> infection may offer a theoretical foundation for breeding resistant tomato varieties. In this study, 11 <i>SlCSE</i> family members were identified from the tomato genome using bioinformatics analyses. Public transcriptome databases and RT-qPCR experiments were used to analyze gene expression in tomato tissues, responses to <i>Botrytis cinerea</i> infection, and the temporal characteristics of the response to 2-ethylfuran treatment during infection. These experiments resulted in the identification of the key gene <i>SlCSE06</i>. Transgenic tomato lines that overexpressed <i>SlCSE06</i> were constructed to examine their resistance levels to gray mold disease. Many <i>SlCSE</i> genes were upregulated when tomato fruit were infected with <i>Botrytis cinerea</i> during the ripening stage. Furthermore, 24 h after treatment with 2-ethylfuran, most <i>SlCSE</i> genes exhibited increased expression levels compared with the control group, but they exhibited significantly lower levels at other time points. Thus, 2-ethylfuran treatment may enhance the responsiveness of <i>SlCSEs</i>. Based on this research, <i>SlCSE06</i> was identified as the key gene involved in the response to <i>Botrytis cinerea</i> infection. The <i>SlCSE06</i>-overexpressing (OE6) tomato plants exhibited a 197.94% increase in expression levels compared to the wild type (WT). Furthermore, the lignin content in OE6 was significantly higher than in WT, suggesting that the overexpression of <i>SlCSE06</i> enhanced lignin formation in tomato plants. At 5 days post-inoculation with <i>Botrytis cinerea</i>, the lesion diameter in OE6 decreased by 31.88% relative to the WT, whereas the lignin content increased by 370.90%. Furthermore, the expression level of <i>SlCSE06</i> was significantly upregulated, showing a 17.08-fold increase compared with the WT. These findings suggest that 2-ethylfuran enhances the activation of the critical tomato disease resistance gene <i>SlCSE06</i> in response to gray mold stress, thereby promoting lignin deposition to mitigate further infection by <i>Botrytis cinerea</i>.