Defense response of a pepper cultivar cv. Sy-2 is induced at temperatures below 24°C

Temperature is one of the most important environmental factors that influence plant growth and development. Recent studies imply that plants show various responses to non-extreme ambient temperatures. Previously, we have found that a pepper cultivar cv. Sy-2 (Capsicum chinense) shows developmental defects at temperatures below 24°C. In this study, to gain new insights into the temperature sensitivity of cv. Sy-2, temperature-sensitive genes were screened using microarray techniques. At restrictive temperature of 20°C, almost one-fourth of the 411 up-regulated genes were defense related or predicted to be defense related. Further expression analyses of several defense-related genes showed that defense-related genes in cv. Sy-2 were constitutively expressed at temperatures below 24°C. Moreover, accumulation of high level of salicylic acid (SA) in cv. Sy-2 grown at 20°C suggests that the defense response is activated in the absence of pathogens. To confirm that the defense response is induced in cv. Sy-2 below 24°C, we evaluated the resistance to biotrophic bacterial pathogen Xanthomonas campestris pv. vesicatoria and necrotrophic fungal pathogen Cercospora capsici. Cv. Sy-2 showed enhanced resistance to X. campestris pv. vesicatoria, but not to C. capsici.