Paula Moolhuijzen, Cynthia Ge, Elzette Palmiero & Simon R. Ellwood

Theoretical and Applied Genetics June 2023; vol. 136, Article number: 145

Key message

Gene expression at the RBgh2 locus indicates involvement in cAMP/G-protein-coupled signalling and innate immunity in barley powdery mildew adult plant resistance.

Abstract

Barley powdery mildew is a globally significant disease, responsible for reduced grain yield and quality. A major effect adult plant resistance gene, RBgh2, was previously found in a landrace from Azerbaijan. The atypical phenotype suggested different underlying genetic factors compared to conventional resistance genes and to investigate this, genome-wide gene expression was compared between sets of heterogeneous doubled haploids. RBgh2 resistance is recessive and induces both temporary genome-wide gene expression changes during powdery mildew infection together with constitutive changes, principally at the RBgh2 locus. Defence-related genes significantly induced included homologues of genes associated with innate immunity and pathogen recognition. Intriguingly, RBgh2 resistance does not appear to be dependent on salicylic acid signalling, a key pathway in plant resistance to biotrophs. Constitutive co-expression of resistance gene homologues was evident at the 7HS RBgh2 locus, while no expression was evident for a 6-transmembrane gene, predicted in silico to contain both G-protein- and calmodulin-binding domains. The gene was disrupted at the 5′ end, and G-protein-binding activity was suppressed. RBgh2 appears to operate through a unique mechanism that co-opts elements of innate immunity.

See https://link.springer.com/article/10.1007/s00122-023-04392-0

Figure 2: Gene expression and GO term differences between RBgh2 barley powdery mildew-resistant and -susceptible DH lines. a An overview of the RNA experimental design and grouped sample comparisons. b Venn diagram of significantly differentially expressed genes (SDEGs). Groups I and II represent Bgh-inoculated APR and susceptible lines relative to their respective control samples, and group III represents APR Bgh-inoculated relative to susceptible Bgh-inoculated samples. c Plots for significant GO term enrichments for SDEGs. Biological processes, cellular components and molecular functions are shown from left to right. The y-axis displays the ratio of significantly DEGs/total number of genes annotated for a GO term (in the barley genome) for each group comparison (x-axis), with the same comparison groups as in b. GO terms represented by induced genes have positive values on the y-axis and suppressed genes by negative values on the y-axis