Map-based cloning identifies a missense SNP in CsTRX z, encoding a z-type thioredoxin homolog, as the genetic determinant of Dominant Virescent Leaf in cucumber.

key messageA missense SNP G → A mutation in the z-type thioredoxin-coding gene CsTRX z (CsDVL) reveals its pivotal regulatory function in chloroplast development, chlorophyll homeostasis, and low-temperature-sensitive photosynthetic regulation, with direct implications for targeted genetic improvement in breeding programs. Thioredoxins (TRXs), pivotal redox regulators modulating protein function, are essential for plant stress adaptation, development, and growth. While extensively characterized in model species (e.g., Arabidopsis, rice), their roles in vegetable crops remain underexplored. Here, we report a missense SNP (G → A) in the z-type thioredoxin CsTRX z (CsDVL), identified via ethyl methanesulfonate (EMS) mutagenesis, as the causal variant underlying the Dominant Virescent Leaf phenotype in cucumber (Cucumis sativus). The mutant PSM004 exhibits transient yellow-green cotyledons at seedling emergence, reverting to wild-type pigmentation during later growth stages. Genetic and cytological analyses confirmed that the Dominant Virescent Leaf (DVL) locus perturbs chloroplast ultrastructure, chlorophyll biosynthesis, and photosynthetic efficiency. Positional cloning delimited DVL to a 75.9-Kb region on chromosome 6, with allelic diversity analysis pinpointing a G → A substitution in the fourth exon of CsTRX z as the causative mutation. Transcriptomic profiling revealed that this missense SNP reprograms expression of chloroplast-localized genes governing chlorophyll metabolism, redox homeostasis, carbohydrate flux, and photosynthetic machinery. Physiological assays further demonstrated thermosensitivity in PSM004, with low-temperature treatment (20 °C/15 °C) inducing reversible chlorosis in developing leaves. Our findings elucidate CsTRX z's conserved yet distinct role in chloroplast biogenesis beyond model systems and establish its utility as a genetic target for enhancing stress resilience and photosynthetic performance in cucumber breeding programs.