Tandem 13-Lipoxygenase Genes in a Cluster Confers Yellow-Green Leaf in Cucumber

Some lipoxygenase (LOX) isoenzymes can co-oxidize carotenoids. Carotenoids are collectors of light energy for photosynthesis and can protect plants from reactive oxygen species and coloration. This study isolated the cucumber (Cucumis sativus L.) yellow-green leaf mutant (ygl1), which had yellow-green leaves with decreased chlorophyll synthesis, increased relative carotenoid content, and delayed chloroplast development. Genetic analysis demonstrated that the phenotype of ygl1 was caused by a recessive mutation in a nuclear gene. The bulked segregants were resequenced, and the candidate ygl1 locus identified was mapped to the 9.2 kb region of the chromosome 4. Sequence analysis revealed that ygl1 encodes the tandem 13-LOX genes in a cluster. Four missense mutations were found in four tandem 13-LOX genes (Csa4M286960, Csa4M287550, Csa4M288070, and Csa4M288080) in the ygl1 mutant, and the four 13-LOX genes showed high similarity with one another. The transient RNA interference and virus-induced gene silencing of these genes simultaneously resulted in yellow-green leaves with a reduced amount of chloroplasts and increased relative carotenoid content, which were observed in the ygl1 mutant. This evidence supported the non-synonymous SNPs (Single Nucleotide Polymorphism) in the four tandem 13-LOX genes as being the causative mutation for the yellow-green leaves. Furthermore, this study provides a new allele for breeding cucumbers with yellow-green leaves and serves as an additional resource for studying carotenoid biosynthesis.