CsSE59 Encoding Invertase/Pectin Methyl Esterase Inhibitor Is a Candidate Gene Conferring the Virescent True Leaf Phenotype in Cucumber

Abstract

Leaf color mutants are the ideal materials to study the regulation mechanisms of chlorophyll biosynthesis and chloroplast development or as markers for crop breeding. In this study, we identified a virescent true leaf mutant se59 from the ethyl methane sulfonate (EMS)-induced mutant lines of cucumber (Cucumis sativus L.). The se59 mutant showed normal cotyledons, but the true leaf displays light green at early growth stage, which can recover normal green later. The se59 locus was controlled by a single recessive nuclear gene. The grana stacking in the chloroplasts of se59 decreased significantly, and both the photosynthetic ability and the photosynthetic pigment contents of the se59 were significantly lower than those of wild type. The results of BSA-seq and genotyping showed that an Invertase/Pectin Methyl Esterase Inhibitor (INV/PMEI) protein encoded by CsSE59 is a candidate gene for the virescent true leaf mutant. The expression level of CsSE59 in stem, leaf and root is high. Based on the transcriptome analysis of the first true leaf of se59 mutant, the expression levels of 17 leaf color related genes changed significantly, suggesting CsSE59 may regulate virescent true leaf by interacting with some of these genes in cucumber. The identification of CsSE59 is helpful to clarify the role of INV/PMEI in chloroplast development and to understand the mechanisms of leaf color variation in cucumber.