BioProject

Disease resistance (R) genes encoding intracellular nucleotide-binding domain and Leucine-rich repeat proteins (NLRs) are key components of the plant innate immune system and typically detect the presence of isolate-specific avirulence (AVR) effectors from pathogens. More...

Disease resistance (R) genes encoding intracellular nucleotide-binding domain and Leucine-rich repeat proteins (NLRs) are key components of the plant innate immune system and typically detect the presence of isolate-specific avirulence (AVR) effectors from pathogens. NLRs define the fastest evolving gene family of flowering plants and are often arranged in gene clusters containing multiple paralogs, contributing to extensive copy number and allele-specific NLR variation within a host species. Barley mildew resistance gene locus A (MLA) represents one of only few R genes that have been subject to extreme functional diversification, resulting in allelic resistance specificities each recognizing a cognate but largely unidentified AVRA gene of the powdery mildew fungus, Blumeria graminis f sp hordei (Bgh). We performed RNA-sequencing of Bgh-infected barley leaves at two different time-points to obtain transcriptome data for 16 Bgh isolates, containing different AVRA genes. Subsequently, we analyzed the expression levels in the different isolates with a specific focus on previously described candidate secreted effectors (CSEPs) and additionally performed a transcriptome-wide association analysis including these 16 isolates and the previously published reference isolate DH14. These analyses identified AVRA1 and AVRA13, encoding two CSEPs that are recognized by MLA1 and MLA13 alleles, respectively. The avirulence function of both candidates could be verified by transient expression of the effector genes in barley leaves or protoplasts that was sufficient to trigger an MLA1 or MLA13 allele-specific cell death response. AVRA1 recognition by MLA1 is also retained in transgenic Arabidopsis lines. Overall design: Detached leaves of the barley cultivar Pallas or Manchuria were infected with 16 different Bgh isolates, each containing different AVRA effectors. For each isolate, samples were collected at 18 and 48 hours post inoculation (hpi), resulting in a total of 32 RNA-seq samples that were analyzed. Less...