The SlCBL-SlCML24 module mediates silicon-enhanced resistance to bacterial wilt in Solanum lycopersicum

Silicon can enhance plants' disease resistance, although the underlying molecular mechanisms, particularly the role of the calcineurin B-like protein gene SlCBL, remain unclear. To investigate the role of SlCBL in Si-mediated resistance, pharmacological inhibition (Ruthenium Red [RuR], LaCl₃), virus-induced gene silencing (VIGS), CRISPR/Cas9 knockout, and protein interaction assays (yeast two-hybrid, bimolecular fluorescence complementation, pull-down) are used to analyze disease phenotypes, defense gene expression, antioxidant enzyme activities, and protein interactions. Quantitative reverse transcription PCR analysis revealed that Si incorporation upregulated the expression of the tomato ethylene response factor 1 gene (SlERF1) by 1.36-fold and the phenylalanine ammonia-lyase (SlPAL) by 2.27-fold. Upon inoculation with Ralstonia solanacearum, Si introduction further enhanced the expression of SlPR1, SlERF1, and SlPAL (by 1.22-, 1.27-, and 1.06-fold, respectively). Notably, Si induced a dramatic 96.88-fold increase in the expression of SlCBL in inoculated, Si-treated plants. Blocking calcium channels with RuR or LaCl₃ restricts silicon-mediated induced resistance. SlCBL-deficient plants (due to VIGS or CRISPR/Cas9) exhibit increased susceptibility, more severe wilting, higher disease indices, reduced expression of defense genes (SlPR1, SlERF1, SlPAL), and lower of antioxidant enzyme (CAT, POD, SOD) activities. Furthermore, SlCBL physically interacts with the calmodulin-like protein SlCML24. The findings presented herein suggest that Si activates an SlCBL-SlCML24 calcium signaling module to enhance tomato plants' resistance to bacterial wilt, thus providing evidence for a molecular mechanism underlying Si-based disease control.