Transcriptional Profiling of Soft-rot Resistant Transgenic Chinese Cabbage (Brassica rapa L.) Constitutively Overexpressing a Human Cathelicidin Antimicrobial Peptide (hCAP18/LL-37)

Soft rot disease caused by Pectobacterium carotovorum subsp. carotovorum (Pcc), is one of the most devastating diseases affecting the cruciferous plants industry worldwide. In our previous study, the soft rot-resistant transgenic Chinese cabbage (Brassica rapa L.) plants were produced via constitutively overexpressing a human cathelicidin antimicrobial peptide (hCAP18/LL-37). To unravel the molecular mechanisms underlying Pcc resistance of the transgenic plants, this study compares the global transcriptional profile of untransformed line (WT) and the transgenic lines (TG23, TG34) through hybridization with KBGP-24K, Chinese cabbage GeneChip. In total, 1,415 differentially expressed genes (DEGs) were identified, 910 of which were up-regulated, while 505 were down-regulated. The DEGs were classified into 31 categories after Gene ontology (GO) annotation, in which 68 genes are in response to stimulus and are involved in immune system process, 12 genes are related to cell wall, and 13 genes belong to transcription factors. These genes and those related to toxin and terpenoid metabolism, glutathione metabolism, biosynthesis of phenylpropanoids, and plant hormones were hypothesized to play major roles in the soft rot resistance of transgenic lines (TG23, TG34). Semiquantitative RT-PCR analysis showed that the transcript levels of several candidate genes in TG23 and TG34 were significantly higher than in WT both before and after Pcc inoculation, indicating their potential association with soft rot disease.