RAR1, ROR1, and the Actin Cytoskeleton Contribute to Basal Resistance to Magnaporthe grisea in Barley

Abstract

The fungus Magnaporthe grisea, the causal agent of rice blast disease, is a major pathogen of rice and is capable of producing epidemics on other cultivated cereals, including barley (Hordeum vulgare). We explored the requirements for basal resistance of barley against a compatible M. grisea isolate using both genetic and chemical approaches. Mutants of the RAR1 gene required for the function of major resistance gene-mediated resistance and mutants of the ROR1 and ROR2 genes required for full expression of cell-wall-penetration resistance against powdery mildew pathogens were examined for macroscopic and microscopic alterations in M. grisea growth and symptoms. RAR1 contributed to resistance in epidermis and mesophyll at different stages of fungal infection dependent on the MLO/mlo-5 status. Whereas no ROR2 effect was detected, ROR1 was found to contribute to cell-wall-penetration resistance, at least in the epidermis. Application of the actin agonist cytochalasin E promoted cell wall penetration by M. grisea in a dose-dependent manner, demonstrating an involvement of the actin cytoskeleton in penetration resistance.

Nonhost Resistance in Arabidopsis-Colletotrichum Interactions Acts at the Cell Periphery and Requires Actin Filament Function

“…Barley ROR2 is the functional homolog of Arabidopsis PEN1 and is required for mlo-mediated broad-spectrum resistance against all tested host barley powdery mildew isolates (Collins et al 2003;Freialdenhoven et al 1996). However, ROR2 is not essential for resistance against strains of the rice blast fungus Magnaporthe grisea that can infect barley (Jarosch et al 2005). The penetration mechanism and hemibiotrophic lifestyle of M. grisea is very similar to that of Colletotrichum species, i.e., both parasites develop melanized appressoria that penetrate directly to produce intracellular hyphae inside living plant cells before later switching to necrotrophy (Koga et al 2004;Perfect et al 1999).…”

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.…”

Differential Requirement of Oryza sativa RAR1 in Immune Receptor-Mediated Resistance of Rice to Magnaporthe oryzae

“…Evaluation of the immune response to M. oryzae in the osrar1 rice mutant Recent evidence suggests that resistance to virulent pathogens in Arabidopsis and barley is dependent on the level of the RAR1 protein (Holt et al, 2005;Jarosch et al, 2005). We previously showed that OsRAR1 functionally rescues the disease resistance of the atrar1 mutant to the virulent P. syringae pv.…”

“…tomato (Pst) DC3000 (Holt et al, 2005) and of barley to the virulent M. oryzae isolate (Jarosch et al, 2005). In rice, the overexpression of OsRAR1 increases the resistance to the virulent Xanthomonas oryzae pv.…”

“…tomato (Pst) DC3000 (Holt et al, 2005). In barley, the loss of RAR1 promotes susceptibility in the mlo-5 genetic background to the Magnaporthe oryzae fungus (Jarosch et al, 2005). These data collectively indicate that RAR1 is required for plant pathogen resistance in diverse genetic backgrounds and species.…”