Genetic Cloning of Genes Controlling Lettuce Leaf Color

Anthocyanidin not only provides health benefits to consumers but also contributes sensory quality to fruits and vegetables such as lettuce. Some cultivars have leaf colors varying from pink to purple due to the presence of different types and concentration of anthocyanidin. Four leaf color segregating populations of lettuce, including one with red spots, were generated. Surprisingly, lettuce leaf color tends to be quantitative trait, controlled by multiple loci. We used a BSA in combination of RNA-seq approach to dissect the genetic loci controlling lettuce leaf color. CAPS markers were designed for each detected locus, and were used to screen the segregating populations for individuals that are heterozygous at a targeted locus but homozygous at other color-controlling loci. The individuals were self-crossed to produce single-locus segregating population (such as F_2:3 sub-population), which was used to fine mapping and genetic cloning of genes controlling lettuce leaf color. Consequently, four genes have been successfully cloned, including two MYB, one bHLH and one ANS (anthocyanindin synthase) gene. Interestingly, one of the detected MYB genes is recessive, likely as a competitor of an active MYB gene. Segregating populations with Mendelian ratio for five additional loci have been generated, and fine mapping and cloning of target genes are underway. Furthermore, genes potentially involved in production of anthocyanindin were identified using net-work analysis, and several novel genes were detected. The molecular mechanism for all genes confirmed to be involved in color formation in lettuce will be investigated in future study.