Plants use a sophisticated immune system to perceive pathogen infection and activate immune responses in a tightly controlled manner. In barley, HvWRKY2 acts as a repressor in barley disease resistance to the powdery mildew fungus, Blumeria graminis f. sp. hordei (Bgh). However, the molecular features of HvWRKY2 in its DNA-binding and repressor functions, as well as its target genes, are uncharacterized. We show that the W-box binding of HvWRKY2 requires an intact WRKY domain and an upstream sequence of ~75 amino acids, and the HvWRKY2 W-box binding activity is linked to its repressor function in disease resistance. Chromatin immunoprecipitation (ChIP)-seq analysis identified HvCEBiP, a putative chitin receptor gene, as a target gene of HvWRKY2 in overexpressing transgenic barley plants. ChIP-qPCR and Electrophoretic Mobility Shift Assay (EMSA) verified the direct binding of HvWRKY2 to a W-box-containing sequence in the HvCEBiP promoter. HvCEBiP positively regulates resistance against Bgh in barley. Our findings suggest that HvWRKY2 represses barley basal immunity by directly targeting pathogen-associated molecular pattern (PAMP) recognition receptor genes, suggesting that HvCEBiP and likely chitin signaling function in barley PAMP-triggered immune responses to Bgh infection.

Triticum urartu, a diploid wild wheat and progenitor of the A genome of bread wheat, is an important resource for resistance to powdery mildew fungus caused by Blumeria graminis f. sp. tritici (Bgt). In the present study we systematically characterized the interaction between the Bgt fungus and T. urartu at the microscopic level. We also tested 227 T. urartu accessions for reaction to Bgt isolate E09 and discovered previously uncategorized powdery mildew resistance in this collection. Pm60 is a CC-NB-LRR type powdery mildew resistance gene that has at least three functional alleles, Pm60, Pm60a, and Pm60b. A marker-assisted screen targeting the Pm60 locus identified a non-functional allele of Pm60a, designated as Pm60a′. A sequence comparison of Pm60a′ and Pm60a revealed that they differed by 58 SNPs and one 3-nucleotide deletion. Based on the sequence variations two molecular markers were developed to differentiate the functional Pm60a allele from the non-functional Pm60a′. Our screen revealed the presence of a previously uncharacterized powdery mildew resistance in T. urartu and provides new insights into the Pm60 locus. We believe that the two molecular markers developed here and new T. urartu resistant accessions will facilitate further identification of novel powdery mildew resistance genes and benefit breeding for powdery mildew resistance.