RACE1, a Japanese Blumeria graminis f. sp. hordei isolate, is capable of overcoming partially mlo-mediated penetration resistance in barley in an allele-specific manner.

Takashi Yaeno,Mai Nagano,Hikaru Wanezaki,Naoto Yamaoka,Kappei Kobayashi,Kazuhiro Sato,Hiroshi Inoue,Ayaka Eishima,Miki Wahara,Hirotaka Toda,Hiroshi Hisano,Masamichi Nishiguchi,Richard A Wilson

doi:10.1371/journal.pone.0256574

Abstract

Loss-of-function mutation of the MILDEW RESISTANCE LOCUS O (Mlo) gene confers durable and broad-spectrum resistance to powdery mildew fungi in various plants, including barley. In combination with the intracellular nucleotide-binding domain and leucine-rich repeat receptor (NLR) genes, which confer the race-specific resistance, the mlo alleles have long been used in barley breeding as genetic resources that confer robust non-race-specific resistance. However, a Japanese Blumeria graminis f. sp. hordei isolate, RACE1, has been reported to have the potential to overcome partially the mlo-mediated penetration resistance, although this is yet uncertain because the putative effects of NLR genes in the tested accessions have not been ruled out. In this study, we examined the reproducibility of the earlier report and found that the infectious ability of RACE1, which partially overcomes the mlo-mediated resistance, is only exerted in the absence of NLR genes recognizing RACE1. Furthermore, using the transient-induced gene silencing technique, we demonstrated that RACE1 can partially overcome the resistance in the host cells with suppressed MLO expression but not in plants possessing the null mutant allele mlo-5.

Highlights

Powdery mildew is one of the most widespread diseases of higher plants that is caused by obligate biotrophic ascomycete fungi of the order Erysiphales [1]
Similar to the report that the isolates of Blumeria graminis f. sp. hordei (Bgh) were selected by over 37 cycles of culture on the leaves of HLN70-8 derived from the mlo-9 mutant allele line SZ5139b [38], Lyngkjær et al [26] had found that the Japanese isolate, RACE1, overcame the mlo-mediated resistance in the mutant allele lines, M66, M.C.20, SR1, SR7, and Atem and Totem
Most mlo accessions have been bred with nucleotide-binding domain and leucine-rich repeat receptor (NLR) genes such as Mla8 and the spread of RACE1 infection would not occur, it should be noted that a mutation in the corresponding Avr gene would be possible

Summary

Introduction

Powdery mildew is one of the most widespread diseases of higher plants that is caused by obligate biotrophic ascomycete fungi of the order Erysiphales [1]. 900 species can infect more than 10,000 plant species [2]. The disease causes significant harvest losses in many crop plants such as barley, wheat, tomato, and cucumber [3,4]. As a reasonable strategy to reduce agricultural costs, breeding of disease resistant crops is performed by introgression of resistance (R) genes. Most R genes encode the intracellular nucleotide-binding domain and leucine-rich repeat receptors (NLRs) which recognize either the structure of effector proteins.

Methods

Results

Conclusion