Colonization of barley by the broad-host hemibiotrophic pathogen Phytophthora palmivora uncovers a leaf development dependent involvement of MLO

The discovery of barley MLO demonstrated that filamentous pathogens rely on plant genes to achieve entry and lifecycle completion in barley leaves. Whilst having a dramatic effect on foliar pathogens, it is unclear whether overlapping or distinct mechanisms affect filamentous pathogen infection of roots. To remove the bias connected with using different pathogens to understand colonisation mechanisms in different tissues we have utilized the aggressive hemibiotrophic oomycete pathogen Phytophthora palmivora. P. palmivora colonises root as well as leaf tissues of barley (Hordeum vulgare). The infection is characterized by a transient biotrophy phase with formation of haustoria. Barley accessions varied in degree of susceptibility, with some accessions fully resistant to leaf infection. Notably, there was no overall correlation between degree of susceptibility in roots compared to leaves suggesting that variation in different genes influences host susceptibility above- and belowground. In addition, a developmental gradient influenced infection, with more extensive colonisation observed in mature leaf sectors. The mlo5 mutation attenuates P. palmivora infection, but only in young leaf tissues. The barley - P. palmivora interaction represents a simple system to identify and compare genetic components governing quantitative colonisation in diverse barley tissue types.This work was supported by the Gatsby Charitable Foundation (RG62472), by the Royal Society (RG69135) and by European Research Council (ERC-2014-STG, H2020, 637537 to SS).This is a metadata record relating to an article that cannot be shared due to publisher copyright