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Characterization of a Tryptophan 2-Monooxygenase Gene from Puccinia graminis f. sp. tritici Involved in Auxin Biosynthesis and Rust Pathogenicity

March 2014 , Volume 27 , Number  3
Pages  227 - 235

Chuntao Yin,1 Jeong-Jin Park,2 David R. Gang,2 and Scot H. Hulbert1

1Department of Plant Pathology and 2Institute of Biological Chemistry, Washington State University, Pullman 99164-6430, U.S.A.

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Accepted 11 December 2013.

The plant hormone indole-3-acetic acid (IAA) is best known as a regulator of plant growth and development but its production can also affect plant–microbe interactions. Microorganisms, including numerous plant-associated bacteria and several fungi, are also capable of producing IAA. The stem rust fungus Puccinia graminis f. sp. tritici induced wheat plants to accumulate auxin in infected leaf tissue. A gene (Pgt-IaaM) encoding a putative tryptophan 2-monooxygenase, which makes the auxin precursor indole-3-acetamide (IAM), was identified in the P. graminis f. sp. tritici genome and found to be expressed in haustoria cells in infected plant tissue. Transient silencing of the gene in infected wheat plants indicated that it was required for full pathogenicity. Expression of Pgt-IaaM in Arabidopsis caused a typical auxin expression phenotype and promoted susceptibility to the bacterial pathogen Pseudomonas syringae pv. tomato DC3000.

© 2014 The American Phytopathological Society