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Functional Contribution of Chorismate Synthase, Anthranilate Synthase, and Chorismate Mutase to Penetration Resistance in Barley--Powdery Mildew Interactions

March 2009 , Volume 22 , Number  3
Pages  311 - 320

Pingsha Hu,1,2 Yan Meng,2 and Roger P. Wise1,2,3

1Interdepartmental Genetics Program, Iowa State University, 2Department of Plant Pathology and Center for Plant Responses to Environmental Stresses, Iowa State University, and 3Corn Insects and Crop Genetics Research, United States Department of Agriculture--Agricultural Research Service, Iowa State University, Ames 50011-1020, U.S.A.

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Accepted 5 November 2008.

Plant processes resulting from primary or secondary metabolism have been hypothesized to contribute to defense against microbial attack. Barley chorismate synthase (HvCS), anthranilate synthase α 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, the causal agent of powdery mildew disease. Single-cell transient-induced gene silencing of HvCS and HvCM1 in mildew resistance locus a (Mla) compromised cells resulted in increased susceptibility. Correspondingly, overexpression of HvCS, HvASa2, and HvCM1 in lines carrying mildew resistance locus o (Mlo), a negative regulator of penetration resistance, significantly decreased susceptibility. Barley stripe mosaic virus--induced gene silencing of HvCS, HvASa2, and HvCM1 significantly increased B. graminis f. sp. hordei penetration into epidermal cells, followed by formation of haustoria and secondary hyphae. However, sporulation of B. graminis f. sp. hordei was not detected on the silenced host plants up to 3 weeks after inoculation. Taken together, these results establish a previously unrecognized role for the influence of HvCS, HvASa2, and HvCM1 on penetration resistance and on the rate of B. graminis f. sp. hordei development in Mla-mediated, barley--powdery mildew interactions.

The American Phytopathological Society, 2009