Barley Rom1 antagonizes Rar1 function in Magnaporthe oryzae‐infected leaves by enhancing epidermal and diminishing mesophyll defence

Abstract

Summary• Barley (Hordeum vulgare) is a host for Blumeria graminis f. sp. hordei (Bgh), which causes powdery mildew, and for the rice blast pathogen Magnaporthe oryzae. It has previously been shown that Rar1, initially identified in a mutational screen as being required for Mla12-specified Bgh-resistance, also controlled pathogenic growth of M. oryzae in barley. Here, we tested whether the rom1 mutation (restoration of Mla12-specified resistance), which restored resistance against Bgh in a susceptible rar1-2 genetic background, also influences the interaction between barley and M. oryzae.• Disease severity after infection with M. oryzae was analysed on rar1-2 mutants and rar1-2 rom1 double mutants. Microscopy and northern analysis were used to gain insight into cellular and molecular events.• On rar1-2 rom1 double mutant plants, the number of M. oryzae disease lesions was increased in comparison to the wild-type and the rar1-2 mutant which correlated with augmented epidermal penetration. However, a decrease in the lesion diameter, apparently conditioned in the mesophyll, was also observed.• These results highlight the impact of Rom1 in basal defence of barley against different pathogens. Importantly, a tissue-specific function for Rom1 with contrasting effects on epidermal and mesophyll defence was demonstrated.

OsWRKY22, a monocot WRKY gene, plays a role in the resistance response to blast

“…facultative versus obligate biotrophy. Ambivalent responses against these pathogens have been reported previously for barley (Jarosch et al ., 1999; Zellerhoff et al ., 2008). In addition, a significantly higher H 2 O 2 production following inoculation with the avirulent M. oryzae strain, as well as with the nonhost Bgh isolate, was observed.…”

“…The inoculated leaf samples of the wrky22 mutant and wild‐type were examined by light microscopy. Callose was stained by the method reported in Zellerhoff et al . (2008).…”

Barley stripe mosaic virus-induced gene silencing (BSMV-IGS) as a tool for functional analysis of barley genes potentially involved in nonhost resistance

“…5,6 Mechanistically this nonhost type of resistance appears to be based on a more efficient execution of different defense strategies, i.e., formation of papillae and onset of the hypersensitive response, also known from attacked epidermal cells in the host interaction. 7,8 Here, we summarize our efforts to characterize the NHR of barley against Magnaporthe at the molecular level using transcriptome profiling and VIGS.…”

Ectoparasitic growth of Magnaporthe on barley triggers expression of the putative barley wax biosynthesis gene CYP96B22 which is involved in penetration resistance

“…Doing so and comparing these control plants with those showing the highest reduction in CYP96B22 transcript abundance, a significant decrease in the frequency of papillae at sites of attempted penetration by the Magnaporthe nonhost isolate CD180 was observed (Figure  4). Since this latter result went along with more epidermal cells showing deposition of autofluorescent material at entire cell walls, this is indicative of ineffective papillae which could not block Magnaporthe penetration [11,23,40]. The more rapid transition of fungal invasion across cell walls became even more obvious in the barley host interaction with M. oryzae isolate TH6772 where CYP96B22 silencing led to an increase of invasive hyphae in attacked epidermal cells.…”