A pathogen-induced putative NAC transcription factor mediates leaf rust resistance in barley

Abstract

Leaf rust, caused byPuccinia hordei, is one of the most widespread and damaging foliar diseases affecting barley (Hordeumspp.). The barley leaf rust resistance locusRph7, located on the short arm of chromosome 3H, confers defence at all growth stages and was previously shown to have unusually high sequence and haplotype divergence. Earlier, four candidate genes forRph7were reported and, despite an in-depth comparative sequence analysis and haplotypic characterisation, the causal gene could not be resolved. Here, we successfully clonedRph7utilising a fine mapping approach in combination with an RNA-Seq based expression analysis. We identified three up-regulated and pathogen-induced genes with presence/absence variation (PAV) at this locus. Sequence analysis of chemically inducedRph7knockout mutant lines identified multiple independent non-synonymous variants, including a premature stop codon in a single non-canonical resistance gene that encodes a 302-amino acid protein. Progeny from four independent transgenic lines segregated for the expected avirulentRph7infection type in response to several avirulentP. hordeipathotypes, however, all plants were susceptible to a single virulent pathotype confirming the specificity. Structural analysis using an AlphaFold2 protein model suggests thatRph7encodes a putative NAC transcription factor, as it shares structural similarity to ANAC019 from Arabidopsis, with a C-terminal BED domain. A global gene expression analysis suggestsRph7is involved in the activation of basal defence.

Resistance that stacks up: engineering rust and mildew disease control in the cereal crops wheat and barley

“…For example, two recent studies utilized sequenced chromosome‐scale assemblies from the wheat and barley pan‐genomes to clone the leaf rust R genes Leaf rust 14a ( Lr14a ) (Kolodziej et al ., 2021) and Resistance to Puccinia hordei 3 ( Rph3 ) (Dinh et al ., 2022) from wheat and barley, respectively. Most recently the resistance gene Rph7 was cloned using comparative sequence and expression analysis utilizing the updated barley pan‐genome (Chen et al ., 2022). Lr14a , Rph3 and Rph7 encode an ankyrin membrane‐bound repeat protein, putative executor protein and NAC transcription factor, respectively, which are race‐specific non‐canonical resistance proteins.…”

The wheat stripe rust resistance gene YrNAM is Yr10

“…YrNAM encodes a non-canonical resistance protein with a NAM (No Apical Meristem) domain and a ZnF (Zinc Finger)-BED domain at the N and C termini, respectively 5 . It is structurally similar to Rph7, a leaf rust resistance gene in barley containing NAC transcription factor (TF) and ZnF-BED domains 8 . Together YrNAM and Rph7 represent a different class of R proteins, which we propose be designated as Triticeae NAC-BED domain (TNB) proteins.…”