Fine mapping and identification of candidate genes for the sy-2 locus in a temperature-sensitive chili pepper (Capsicum chinense).

KEY MESSAGE: The sy - 2 temperature-sensitive gene from Capsicum chinense was fine mapped to a 138.8-kb region at the distal portion of pepper chromosome 1. Based on expression analyses, two putative F-box genes were identified as sy - 2 candidate genes. Seychelles-2 ('sy-2') is a temperature-sensitive natural mutant of Capsicum chinense, which exhibits an abnormal leaf phenotype when grown at temperatures below 24 °C. We previously showed that the sy-2 phenotype is controlled by a single recessive gene, sy-2, located on pepper chromosome 1. In this study, a high-resolution genetic and physical map for the sy-2 locus was constructed using two individual F2 mapping populations derived from a cross between C. chinense mutant 'sy-2' and wild-type 'No. 3341'. The sy-2 gene was fine mapped to a 138.8-kb region between markers SNP 5-5 and SNP 3-8 at the distal portion of chromosome 1, based on comparative genomic analysis and genomic information from pepper. The sy-2 target region was predicted to contain 27 genes. Expression analysis of these predicted genes showed a differential expression pattern for ORF10 and ORF20 between mutant and wild-type plants; with both having significantly lower expression in 'sy-2' than in wild-type plants. In addition, the coding sequences of both ORF10 and ORF20 contained single nucleotide polymorphisms (SNPs) causing amino acid changes, which may have important functional consequences. ORF10 and ORF20 are predicted to encode F-box proteins, which are components of the SCF complex. Based on the differential expression pattern and the presence of nonsynonymous SNPs, we suggest that these two putative F-box genes are most likely responsible for the temperature-sensitive phenotypes in pepper. Further investigation of these genes may enable a better understanding of the molecular mechanisms of low temperature sensitivity in plants.