The barley leaf rust resistance gene Rph3 encodes a predicted membrane protein and is induced upon infection by avirulent pathotypes of Puccinia hordei

Abstract

Leaf rust, caused by Puccinia hordei, is an economically significant disease of barley, but only a few major resistance genes to P. hordei (Rph) have been cloned. In this study, gene Rph3 was isolated by positional cloning and confirmed by mutational analysis and transgenic complementation. The Rph3 gene, which originated from wild barley and was first introgressed into cultivated Egyptian germplasm, encodes a unique predicted transmembrane resistance protein that differs from all known plant disease resistance proteins at the amino acid sequence level. Genetic profiles of diverse accessions indicated limited genetic diversity in Rph3 in domesticated germplasm, and higher diversity in wild barley from the Eastern Mediterranean region. The Rph3 gene was expressed only in interactions with Rph3-avirulent P. hordei isolates, a phenomenon also observed for transcription activator-like effector-dependent genes known as executors conferring resistance to Xanthomonas spp. Like known transmembrane executors such as Bs3 and Xa7, heterologous expression of Rph3 in N. benthamiana induced a cell death response. The isolation of Rph3 highlights convergent evolutionary processes in diverse plant-pathogen interaction systems, where similar defence mechanisms evolved independently in monocots and dicots.

The genetic basis and interaction of genes conferring resistance to Puccinia hordei in an ICARDA barley breeding line GID 5779743

“…Morex, while Morex is susceptible to P. hordei pathotype 5457 P+, the RphGID locus may not exist in this accession. Many disease resistance genes isolated so far such as the genes conferring resistance to Xanthomonas bacteria in rice and pepper ( Yoshimura et al, 1998 ; Wu et al, 2008 ; Wang et al, 2015 , 2018 ), and especially the barley leaf rust resistance gene Rph3 ( Dinh et al, 2022 ) encode other types of protein without any conserved domains. In our study, we were not able to pinpoint whether all the identified genes in ORF region play role in providing resistance against all the six pathotypes used in this study and therefore further studies on validation of these genes is highly recommended.…”

“…The total DNA from leaf samples was extracted using the SDS method as previously described by Dinh et al (2022) . About 30 mg of the first leaf of each seedling was sampled into a 96-well collection tube (12 × 8 wells) containing two ball bearings and subjected to DNA extraction using an SDS method.…”

“…Specific markers to detect the presence/absence of Rph3 ( Dinh et al, 2022 ), Rph7 (Dracatos, unpublished), and Rph15 ( Chen et al, 2021 ) were used ( Supplementary Table 3 ).…”

“…Notably, all the ASR genes conferring resistance to P. hordei identified so far are dominant. Up to date, only four out of 28 Rph genes have been isolated, with three genes encoding proteins of the Nucleotide-Binding Leucine-Rich Repeat (NLR) family ( Dracatos et al, 2019 ; Wang et al, 2019 ; Chen et al, 2021 ) and one gene encoding protein of a distinct class ( Dinh et al, 2022 ).…”

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and Singh D (2022) The genetic basis and interaction of genes conferring resistance to Puccinia hordei in an ICARDA barley breeding line GID 5779743.

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