A major QTL and candidate genes for capsaicinoid biosynthesis in the pericarp of Capsicum chinense revealed using QTL-seq and RNA-seq.

Abstract

A major QTL and candidate genes controlling capsaicinoid content in the pericarp were identified by QTL-seq and RNA-seq in Capsicum chinense. Capsaicinoid biosynthesis was previously thought to be restricted to the placental tissue; however, the recent discovery of their biosynthesis in the pericarp provides new opportunities to increase the capsaicinoid content in pepper fruits. Currently, the genetic mechanisms regulating capsaicinoid biosynthesis in the pericarp remain unknown. Here, we performed quantitative trait loci (QTL) mapping and RNA sequencing (RNA-seq) to reveal the genes controlling capsaicinoid biosynthesis in the pericarp. A whole-genome sequencing-based QTL-seq strategy was employed, identifying a major QTL on chromosome 6. To validate the QTL on chromosome 6, we performed traditional QTL mapping using the same population in QTL-seq with an additional biparental population. A total of 15 QTLs for capsaicinoid content distributed on chromosomes 3, 6, and 11 were newly identified. Among these QTLs, the genetic loci on the lower arm of chromosome 6 were commonly detected in the two mapping populations, corresponding to the location of the major QTL detected using whole-genome sequencing-based QTL-seq. Our RNA-seq analysis identified candidate genes within the common QTL that were differentially expressed in the pungent and non-pungent pericarp tissues. Our results are expected to contribute to the elucidation of the regulation of capsaicinoid biosynthesis. We also demonstrated that a combination of QTL mapping and RNA-seq is helpful for refining the candidate genes of a complicated trait of interest.