ESTs-SSR And Gene Expresion Analyses Of Systemic Acquired Resistance In Chinese Cabbage (Brassica Campestris L.ssp Pekinensis) Resistant To Turnip Mosaic Virus (TuMV)

Turnip mosaic virus (TuMV) is one of the most important viruses infecting Chinese cabbage (Brassica campestris L.ssp pekinensis). EST-derived SSR markers were firstly developed. 7,714 contigs were obtained by assembling 13,007 expressed sequence tags (ESTs) of Chinese cabbage and SSRs were screened from the contigs. 890 (10.4%) of the ESTs were found containing SSRs (SSR-ESTs) in the non-redundant ESTs with an average distance approximately 3.9kb between SSRs. 123 EST-SSR primer pairs which amplified DNA frgaments longer than 14bp were designed for EST-SSR markers analysis in the inbreed lines of Chinese cabbage, two were highly resistant and two highly susceptible to TuMV. 37 SSR markers amplified successfully but did not display polymorphism, and only 23 (18.7%) showed polymorphism in at least one of the inbreed lines.To understand the molecular basis of Chinese cabbage resistance to TuMV, a highly resistant and a highly susceptible inbreed lines of Chinese cabbage, which displayed 83.7% identity as revealed by EST-SSR analysis, were inoculated with TuMV-C3 strain, respectively, and used to analyse gene expression in the resistance to TuMV using the Chinese cabbage cDNA microarray constructed at our lab. Total RNA was extracted from non-inoculate leaves (near by inoculated leaves) at 7,14, and 21 days after inoculation. In total, 1749 upregulated and 70 down-regualted genes were detected in the highly resistant inbred lines compared the gene expression in the highly sensitive inbred lines. The upregulated genes include those coding for pathiogenesis-related proteins pathogenesis-related (PR) proteins (PR-2, PR-3, PR-4, PR-5) and some antioxidant enzymes. Genes involved in salicylid acid (SA)- and Jasmom'c acid (JA)- mediated signal transduction pathways were all upregulated at 21 days after inoculation. These genes were considered to be involved in systemic acquired resistance (SAR) to TuMV in the highly resistant inbred line of Chinese cabbage.In this work, EST-SSR markers related to resistance to TuMV in Chinese cabbage were obtained which will be used for genetic linkage map construction and gene locationof Chinese cabbage, and genes involved in systemic acquired resistance to TuMV were screened using cDNA microarray of Chinese cabbage. These genes are importane for understanding the molecualr mechanism of SAR to TuMV in plant.