Disruption of SlCNGC18 enhances Cucumber mosaic virus resistance and drought tolerance in tomato (Solanum lycopersicum L. cv. Micro-Tom)

Abstract

Tomato is a globally important crop that is frequently affected by stress linked to viral infection and drought, both of which significantly reduce yield and quality. Cucumber mosaic virus (CMV) is a major pathogen that induces severe disease symptoms, while drought limits plant growth and productivity in general. Calcium signaling through cyclic nucleotide-gated channels (CNGCs) plays a critical role in plant responses to both biotic and abiotic stresses. However, it remains unclear how the tomato SlCNGC18, a homolog of Arabidopsis thaliana CNGC4 (DND2), regulates viral resistance and drought tolerance in Micro-Tom plants. Using CRISPR/Cas9 gene editing, we generated loss-of-function slcngc18 mutants in tomato (cv. Micro-Tom) and assessed their responses to CMV infection. Drought-related responses were further evaluated using the slcngc18-2 mutant. The mutants showed enhanced resistance to CMV, with more than a threefold reduction in viral accumulation and milder disease symptoms. This resistance was accompanied by a twofold increase in salicylic acid (SA) levels and induction of the defense gene SlPR1, which showed more than sevenfold upregulation. Consistently, SlPBS3 was also upregulated, suggesting its contribution to increased SA levels. Moreover, under drought conditions, slcngc18-2 plants showed approximately sevenfold higher survival rates and reduced water loss compared with wild-type plants. Physiological analyses revealed altered stomatal traits, characterized by smaller stomata with increased stomatal density, along with enhanced abscisic acid (ABA) signaling despite no change in ABA levels. Furthermore, transcriptome profiling indicated downregulation of genes involved in calcium transport and phenylalanine ammonia-lyase. Our results indicate that SlCNGC18 functions as a negative regulator of CMV resistance and drought tolerance-related responses in Micro-Tom. The slcngc18 mutants exhibited elevated SA levels together with enhanced ABA signaling-related gene expression, supporting SlCNGC18 as a promising target for breeding tomato cultivars with improved resilience to multiple stresses. Overall, this study provides new insight into the potential involvement of calcium channel-mediated signaling in hormonal and immune responses during crop stress adaptation.