Transcriptome analysis of high-temperature adult-plant resistance conditioned by Yr39 during the wheat-Puccinia striiformis f. sp tritici interaction

Stripe rust [caused by Puccinia striiformis Westend. f. sp. tritici Eriks. (Pst)] is a destructive disease of wheat (Triticum aestivum L.) worldwide. High-temperature adult-plant (HTAP) resistance to stripe rust is race non-specific, inherited quantitatively and durable. Previously, we identified and mapped the single Yr39 HTAP stripe rust resistance gene in the spring wheat cultivar Alpowa, which was identified on chromosome 7BL and accounted for 64.2% of the variation in resistance. To identify transcripts associated with Yr39-mediated resistance, we selected two F-7 recombinant inbred lines (RILs) from an 'Avocet S/Alpowa' cross that differed at the Yr39 locus to represent an incompatible (Yr39) and compatible (yr39) interaction with Pst. Using the Affymetrix Wheat GeneChip, we profiled the transcript changes occurring in flag leaves of these two RILs over a time-course after treatment with Pst urediniospores and mock-inoculation. This time-course study identified 99 induced transcripts that were classified as HTAP resistance-specific. The temporal pattern of transcript accumulation showed a peak at 48 h after infection, which was supported by microscopic observation of fungal development and quantitative PCR assays that showed a rapid increase in fungal biomass after this time in the compatible interaction. More than half (50.5%) of the annotated transcripts specifically induced during HTAP resistance were involved in defence and/or signal transduction, including R gene homologues and transcripts associated with pathogenesis-related protein production, phenylpropanoid biosynthesis and protein kinase signalling. This study represents the first transcript profiling of HTAP resistance to stripe rust in wheat, and we compare our results with other transcript studies of race-specific and race non-specific resistance.