Wild barley accumulates distinct sets of transcripts in response to pathogens of different trophic lifestyles

Wild barley (Hordeum vulgare subsp. spontaneum) accession 'Shechem 12-32' is resistant to multiple pathogens, including Puccinia hordei and Cochliobolus sativus, causal agents of leaf rust and spot blotch, respectively. Both pathogens begin the infection process as biotrophs, but C. sativus switches to necrotrophism after colonization. It is generally considered that plants require distinct arsenals of genes to successfully respond to either biotrophic or necrotrophic pathogens. To characterize the defense responses initiated by resistant wild barley accession 'Shechem', a temporal survey of transcript abundance after inoculation with P. hordei and C. sativus was conducted using the Barley1 GeneChip. A total of 95 and 299 gene transcripts exhibited significant (p < 0.0001) differential accumulation in response to P. hordei and C. sativus, respectively, compared to mock-inoculated controls, with 21 transcripts (6 defense-related) in common. Quantities of differentially accumulated gene transcripts in response to P. hordei were evenly distributed across examined time points, while over one-half (183) of the differentially accumulating gene transcripts in response to C. sativus were identified at 24 h after infection, the approximate time when the pathogen changes trophic lifestyles. Our results indicate that resistant wild barley exhibits a different host response to biotrophic and hemibiotrophic pathogens, with genes related to oxidative stress having a particularly important role in defense against hemibiotrophs.