Genome-Wide Analysis of Tomato SlCCD Genes and the Role of SlCCD11 in Enhancing Salt Tolerance

Tomato (<i>Solanum lycopersicum</i> L.) is an important horticultural crop. Carotenoid cyclase dioxygenase (CCD) is an enzyme responsible for cleaving carotenoids, which is involved in regulating plant growth and response to abiotic stresses. However, the role of <i>SlCCDs</i> in tomato stress resistance remains unclear. This study used the tomato variety 'Micro-Tom' as the material to investigate the function of <i>SlCCDs</i> in stress responses. Through whole-genome analysis, a total of 12 <i>SlCCDs</i> members (<i>SlCCD1</i>-<i>SlCCD12</i>) were identified. Systematic evolutionary analysis classified them into four branches, and members within the same branch maintained a conserved structure. The promoter analysis revealed that <i>SlCCDs</i> contain multiple hormones and stress response elements. The qRT-PCR analysis revealed that <i>SlCCD11</i> was the most highly expressed gene in the leaves. In addition, multiple <i>SlCCDs</i> showed significant responses to abscisic acid (ABA), methyl jasmonate (MeJA), light, and sodium chloride (NaCl) treatments. Among them, the expression of <i>SlCCD11</i> significantly increased under salt stress. By silencing <i>SlCCD11</i> using virus-induced gene silencing (VIGS) technology, it was found that the chlorophyll content, antioxidant enzyme activity, and ABA-related gene expression in the TRV:<i>SlCCD11</i> plants under salt stress were all lower than the control samples, while the carotenoid content and ROS accumulation were higher. This indicates that <i>SlCCD11</i> is a positive regulatory factor for salt stress. In conclusion, this study systematically analyzed the <i>SlCCD</i> gene family and revealed the positive role of <i>SlCCD11</i> in tomato response to salt stress, providing a candidate gene for genetic improvement of crop stress resistance.