Endochitinase Overexpression in Transgenic Tomato Plants Improves Resistance to Phytopathogens

Engineering broad-spectrum disease resistance remains a major challenge in crop improvement because most resistance genes are effective against a limited range of pathogens. Pathogenesis-related (PR) proteins, particularly endochitinases, are promising targets for enhancing plant immunity due to their antimicrobial activity and ability to activate defense responses. Here, we generated transgenic tomato (Solanum lycopersicum L.) plants overexpressing an endochitinase gene to assess their potential for enhanced resistance against bacterial and fungal pathogens. Three independent overexpression lines and the wild type were evaluated for transgene expression, chitinase activity, defense-related gene expression, and resistance after inoculation with Xanthomonas euvesicatoria pv. perforans (Xep) and Sclerotinia sclerotiorum. The transgene was strongly expressed in all transgenic lines, whereas chitinase activity increased by up to fivefold compared with the wild type. Endochitinase overexpression activated defense responses, with marked induction of PR1 expression, reaching a maximum increase of over 480-fold, and enhanced expression of defense-associated genes, including SlACS and SlACO. Compared with the wild type, the most responsive transgenic lines showed reductions of up to 79.7% in bacterial spot severity and 85.6% in white mold severity. These findings demonstrate that endochitinase overexpression activates defense signaling and improves broad-spectrum resistance, representing a promising strategy for developing disease-resistant tomato cultivars.