Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 6, 2011
Publication Date: May 1, 2011
Citation: Moscou, M.J., Lauter, N.C., Caldo, R.A., Nettleton, D., Wise, R.P. 2011. Quantitative and temporal definition of the Mla transcriptional regulon during barley-powdery mildew interactions. Molecular Plant-Microbe Interactions. 24(6):694-705. Interpretive Summary: Powdery mildew is a devastating fungal disease and also an ideal system to explore the interactions of obligate fungal pathogens with their host plants. A major source of resistance in barley against the powdery mildew pathogen is conferred by the Mla (Mildew resistance locus a) locus. This manuscript describes novel and timely research on parallel expression profiling experiments targeting resistance-gene mediated immunity. To do this, we analyzed time-course expression profiles of barley plants harboring Mla1, Mla6, and Mla12 wild-type alleles versus paired loss-of-function mutants to discover conserved genes that are regulated by Mla. The Barley1 GeneChip is a high-throughput genomic uniform platform to investigate the expression of 22,000 genes simultaneously. By using Barley1 GeneChips to profile gene expression in cultivars containing different barley Mla alleles, and comparing these results to mutant variants, we have used novel bioinformatic methods to identify transcriptional targets of Mla-mediated resistance. We have shown that these gene targets function in diverse biochemical pathways; however, they are all being coordinately expressed together in the proper time and place to manifest in plant disease defense. Molecular markers for these gene targets can be used by breeders to successfully combat devastating diseases. Since Triticeae cereal grains are one of our most important food sources, these findings provide new knowledge of broad significance to plant scientists, and will help to produce high quality barley grain with better yields, benefitting growers and producers.
Technical Abstract: Barley Mildew resistance locus a (Mla) is a major determinant of immunity to the powdery mildew pathogen, Blumeria graminis f. sp. hordei. Alleles of Mla encode cytoplasmic- and membrane-localized coiled-coil, nucleotide binding site, leucine-rich repeat proteins that mediate resistance when complementary avirulence effectors (AVRa) are present in the pathogen. Presence of an appropriate AVRa protein triggers nuclear relocalization of MLA, in which MLA binds repressing host transcription factors. Timecourse expression profiles of plants harboring Mla1, Mla6, and Mla12 wild-type alleles versus paired loss-of-function mutants were compared to discover conserved transcriptional targets of MLA and downstream signaling cascades. Pathogen-dependent gene expression was equivalent or stronger in susceptible plants at 20 h after inoculation (HAI) and was attenuated at later timepoints, whereas resistant plants exhibited a time-dependent strengthening of the transcriptional response, increasing in both fold change and the number of genes differentially expressed. Deregulation at 20 HAI implicated 16 HAI as a crucial point in determining the future trajectory of this interaction and was interrogated by quantitative analysis. In total, 28 potential transcriptional targets of the MLA regulon were identified. These candidate targets possess a diverse set of predicted functions, suggesting that multiple pathways are required to mediate the hypersensitive reaction.