A global view of gene-specific disease resistance, basal defense, and the suppression of host-responses

Plant defense to microbial attack is highly dependent upon recognition events involving associated gene products in the host and pathogen. This presentation will review the global framework of host gene expression during biotrophic pathogen invasion via analysis of highly parallel expression profiling experiments. We used the Barley1 GeneChip to analyze the transcriptional regulation of 22,792 host genes throughout various time-course interactions among barley and the powdery mildew fungus, Blumeria graminis f. sp. 432 Barley1 GeneChips, representing 144 replicated barley-powdery mildew interactions, were used to interrogate plants containing allelic variants and mutants of Mla, Rar1, and the Rar1 suppressor, om1. Using linear mixed model analyses, three highly significant and contrasting patterns of expression were revealed among incompatible and compatible interactions. Many of these genes are involved in basal defense pathways where recognition of specific avirulence factors in incompatible interactions leads to the maintenance of increased expression, whereas, compatible interactions lead to active suppression of these genes. Given that candidate genes have been assigned putative functions, what is the contribution of each to the resistance phenotype, why are subsets of genes co-regulated, and what is the molecular mechanism of pathogen-elicited co-expression?