Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/2008
Publication Date: 3/2/2009
Publication URL: http://apsjournals.apsnet.org/doi/abs/10.1094/MPMI-22-3-0311
Citation: Hu, P., Meng, Y., Wise, R.P. 2009. Functional Contribution of Chorismate Synthase, Anthranilate Synthase, and Chorismate Mutase to Penetration Resistance in Barley-Powdery Mildew Interactions. Molecular Plant-Microbe Interactions. 22(3):311-320. Interpretive Summary: The plant immune system, which recognizes and confers resistance to diverse pathogens, is dynamic and complex. Multiple levels of resistance are involved in the plant defense system, such as pre-formed barriers in the cell wall before penetration, inducible antimicrobial products and secondary metabolites during the early stage of invasion, as well as signaling components involved in recognition and systemic acquired resistance. We present functional analysis of three pivotal metabolic enzymes in barley-powdery mildew interactions in the presence or absence of the Mla (Mildew resistance locus a) resistance gene. We provide evidence that these genes play a role in penetration resistance to Blumeria graminis f. sp. hordei, the causal agent of powdery mildew disease of barley. We also show that these genes are involved in temporal regulation of Mla influenced infection kinetics. Genes encoding enzymes that catalyze the formation of secondary metabolites contribute to penetration resistance and pathogen defense. The emerging information on genes that regulate these cellular pathways has important applications in crop improvement.
Technical Abstract: Plant processes resulting from primary or secondary metabolism have been hypothesized to contribute to defense against microbial attack. Barley chorismate synthase (HvCS), anthranilate synthase alpha subunit 2 (HvASa2) and chorismate mutase 1 (HvCM1) occupy pivotal branch-points downstream of the shikimate pathway leading to the synthesis of aromatic amino acids. Here we provide functional evidence that these genes contribute to penetration resistance to Blumeria graminis f. sp. hordei (Bgh), the causal agent of powdery mildew disease. Single-cell Transient Induced Gene Silencing (TIGS) of HvCS and HvCM1 in Mla (Mildew resistance locus a) compromised cells resulted in increased susceptibility. Correspondingly, overexpression of HvCS, HvASa2, and HvCM1 in lines carrying Mlo (Mildew resistance locus o), a negative regulator of penetration resistance, significantly decreased susceptibility. These three genes also play a role in temporal regulation of Mla-influenced infection kinetics. Barley stripe mosaic virus induced gene silencing (BSMV-VIGS) of HvCS, HvASa2, and HvCM1 significantly increased Bgh penetration into epidermal cells, formation of haustoria and secondary hyphae. However, sporulation of Bgh was not detected on the silenced host plants up to three weeks after inoculation. Taken together, these results indicate that expression of these genes is necessary for the kinetics of Mla-mediated defense of barley to Bgh.