Analysis of the Late Blight Response Transcriptome Mediated by the RB Gene from S. bulbocastanum using Sibling Introgression Lines of Potato

Screening of advanced backcross populations derived from S. tuberosum x S. bulbocastanum hybrids identified few elite families exhibiting high level of resistance to the sucking insect Myzus persicae (aphids). One of the best families (Sbu8; Ivory Crisp, recurrent parent) that segregated for aphid resistance also segregated for resistance to multiple isolates of Phytophthora infestans. Detailed analysis of this family of introgression lines identified recombinant sibling lines (Sbu8.5 and Sbu8.15) for further differential analysis. Genomic PCR confirmed that Sbu8.5 but not Sbu8.15 was positive for RB gene introgression. Like its donor parent S. bulbocastanum, Sbu 8.5 was both late blight and aphid resistant, while its sibling line Sbu8.15 was susceptible to aphids and showed only very limited resistance to late blight that was obviously not due to RB introgression. Here we report the initial results of our efforts to dissect the RB-mediated regulatory network in the context of late blight resistance by comparing the sibling backcross derivatives with their donor and recurrent parents. Employing the sampling power of RNA-SEQ, transcriptome libraries were generated for S. bulbocastanum, Sbu8.5, and Sbu8.15 in both control and inoculated conditions. General characterization of the reference-based transcriptome assemblies indicated that differential expression associates resistance with more subtle alterations in expression and susceptibility with more drastic transcriptional changes not necessarily relevant to defense mechanisms. The possible implications of candidate regulatory nodes shared by S. bulbocastanum and Sbu8.5 are discussed in the context of the possible branches that are more important for the expression of RB-mediated resistance.