Enhanced disease resistance caused by BRI1 mutation is conserved between Brachypodium distachyon and barley (Hordeum vulgare).

This study investigated the impact of brassinosteroid (BR)-insensitive 1 (BRI1) mutation, the main receptor of BR in both Brachypodium distachyon and barley, on disease resistance against a range of fungal pathogens of cereals exhibiting different trophic lifestyles. Results presented here show that i) disruption of BRI1 has pleiotropic effects on disease resistance in addition to affecting plant development. BR signaling functions antagonistically with mechanisms of disease resistance that are effective against a broad range of cereal pathogens. ii) Disruption of BRI1 results in increased disease resistance against necrotrophic and hemibiotrophic pathogens that exhibit only a marginal asymptomatic phase but has no effect on biotrophic pathogens or those with a prolonged asymptomatic phase, and iii) disruption of BRI1 has a similar effect on disease resistance in B. distachyon and barley, indicating that defense mechanisms are conserved between these species. This work presents the first evidence for conservation of disease resistance mechanisms between the model species B. distachyon and the cereal crop barley and validates B. distachyon for undertaking model-to-crop translation studies of disease resistance.

Brachypodium distachyon exhibits compatible interactions with Oculimacula spp. and Ramularia collo-cygni, providing the first pathosystem model to study eyespot and ramularia leaf spot diseases.

Brachypodium distachyon (Bd) has established itself as an essential tool for comparative genomic studies in cereals and increasing attention is being paid to its potential as a model pathosystem. Eyespot and ramularia leaf spot (RLS) are important diseases of wheat, barley and other small-grain cereals for which very little is known about the mechanisms of host resistance despite urgent requirements for plant breeders to develop resistant varieties. This work aimed to test the compatibility of interaction of two Bd accessions with the cereal pathogens Oculimacula spp. and Ramularia collo-cygni, the causal agents of eyespot and RLS diseases, respectively. Results showed that both Bd accessions developed symptoms similar to those on the natural host for all pathogen species tested. Microscopy images demonstrated that R. collo-cygni produced secondary conidia and both Oculimacula spp. formed characteristic infection structures on successive tissue layers. Visual disease assessment revealed that quantitative differences in disease severity exist between the two Bd accessions. The results presented here provide the first evidence that Bd is compatible with the main causal agents of eyespot and RLS diseases, and suggest that future functional genetic studies can be undertaken to investigate the mechanisms of eyespot and RLS disease resistance using Bd.