Differential Gene Expression in Cotton Defence Response to Verticillium dahliae by SSH

Verticillium dahliae Kleb. is a necrotrophic plant pathogen that causes serious soil-borne vascular disease in cotton. The molecular basis of cotton response to this pathogen is poorly understood. To capture a wide spectrum of differentially expressed genes in the cotton defence response, RNA isolated from Gossypium barbadense was employed to generate highly enriched transcripts by polymerase chain reaction (PCR)-select suppression subtractive hybridization (SSH). A total of 211 unique genes were differentially identified and classified into 11 functional categories. The largest groups contain genes involved in metabolism, stress/defence response, cell structure and signal transduction. More than one-third of the genes (38%) were identified as unknown classification or function. Northern blot analysis and quantitative real-time PCR (qPCR) were performed to investigate the expression patterns of some representative genes and characterize the role of some signal molecules (H2O2, ethylene, jasmonic acid and salicylic acid) in the cotton defence response. This study identified a set of disease-related genes involved in the process of the response, including pathogenesis-related genes of various classes, oxidative burst-related genes and secondary metabolism-related genes. The characterization of some transcription factors and kinases enabled us to better understand the defence mechanisms. Our results suggested that a complicated and concerted mechanism involving multiple pathways including salicylic acid, jasmonic acid and ethylene was responsible for the cotton defence response to V. dahliae. The expression changes of the ethylene biosynthesis and response genes (ACO1, ACS6, EIN2 and ERF1) in the response of both susceptible and resistant cultivars to V. dahliae indicated that ethylene played a putative role in the resistant response as a signal molecule to trigger defence mechanisms and in the development of disease symptoms by interacting with other molecules.