Comparative transcriptome analysis of wheat cultivars in response to Xanthomonas translucens pv. cerealis and its T2SS, T3SS and TALEs deficient strains

Xanthomonas translucens pv. cerealis causes bacterial leaf streak disease on small grain cereals. Type II and III secretion systems (T2SS and T3SS) play a pivotal role in the pathogenicity of the bacterium, while no data is available on the transcriptome profile of wheat cultivars infected with either wild type or mutants of the pathogen. In this study, wild type, TAL-effector mutants, and T2SS/T3SS mutants of X. translucens pv. cerealis strain NXtc01 were evaluated for their effect on the transcriptome profile of two wheat cultivars i.e. Chinese Spring and Yangmai-158, using Illumina RNA-sequencing technology. RNA-seq data showed that the number of differentially-expressed genes (DEGs) was higher in Yangmai-158 cultivar than in the Chinese Spring, suggesting higher susceptibility of Yangmai-158 to the pathogen. In T2SS, most suppressed DEGs were related to transferase, synthase, oxidase, WRKY, and bHLH transcription factors. The gspD mutants showed significantly decreased disease development in wheat, suggesting an active contribution of T2SS in virulence. Moreover, the gspD mutant restored full virulence and its multiplication in planta by addition of gspD in trans. In T3SS deficient strain, down-regulated DEGs were associated with cytochrome, peroxidases, kinases, phosphatases, WRKY, and ethylene-responsive transcription factors. In contrast, up-regulated DEGs were trypsin inhibitors, cell number regulators, and calcium transporter. Transcriptome analyses coupled with qRT-PCR indicated that some genes are upregulated in Δtal1/Δtal2 compared to tal-free strain, but no direct interaction was observed. These results provide novel insight into wheat transcriptomes in response to X. translucens infection and pave the path for understanding host-pathogen interactions.