Characterization and genetic analysis of a low-temperature-sensitive mutant, sy-2, in Capsicum chinense

A temperature-sensitive mutant of Capsicum chinense, sy-2, shows a normal developmental phenotype when grown above 24°C. However, when grown at 20°C, sy-2 exhibits developmental defects, such as chlorophyll deficiency and shrunken leaves. To understand the underlying mechanism of this temperature-dependent response, phenotypic characterization and genetic analysis were performed. The results revealed abnormal chloroplast structures and cell collapse in leaves of the sy-2 plants grown at 20°C. Moreover, an excessive accumulation of reactive oxygen species (ROS) resulting in cell death was detected in the chlorophyll-deficient sectors of the leaves. However, the expression profile of the ROS scavenging genes did not alter in sy-2 plants grown at 20°C. A further analysis of fatty acid content in the leaves showed the impaired pathway of linoleic acid (18:2) to linolenic acid (18:3). Additionally, the Cafad7 gene was downregulated in sy-2 plants. This change may lead to dramatic physiological disorder and alteration of leaf morphology in sy-2 plants by losing low-temperature tolerance. Genetic analysis of an F(2) population from a cross between C. chinense 'sy-2' and wild-type C. chinense 'No. 3341' showed that the sy-2 phenotype is controlled by a single recessive gene. Molecular mapping revealed that the sy-2 gene is located at a genomic region of the pepper linkage group 1, corresponding to the 300 kb region of the Ch1_scaffold 00106 in tomato chromosome 1. Candidate genes in this region will reveal the identity of sy-2 and the underlying mechanism of the temperature-dependent plant response.