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Mol Plant Pathol. 2018 Sep 22. doi: 10.1111/mpp.12749. [Epub ahead of print]

Structural and Functional Insights into Modulation of the Activity of a Flax Cytokinin Oxidase by Flax Rust Effector AvrL567-A.

Author information

1
School of Chemistry and Molecular Biosciences, Australian Infectious Diseases Research Centre and Institute for Molecular Bioscience, University of Queensland, Brisbane, QLD, 4072, Australia.
2
Department of Biology, University of North Carolina, Chapel Hill, North Carolina, 27599-3280, USA.
3
Commonwealth Scientific and Industrial Research Organisation Agriculture and Food, Canberra, ACT, 2601, Australia.
4
Division of Plant Sciences, Research School of Biology, Australian National University, Canberra, ACT, 2601, Australia.
5
RIKEN Center for Sustainable Resource Science, Yokohama, Kanagawa, 230-0045, Japan.
6
Commonwealth Scientific and Industrial Research Organisation Agriculture and Food, Adelaide, SA, 5064, Australia.
7
Australian Synchrotron, Macromolecular crystallography, Clayton, Victoria, 3168, Australia.

Abstract

During infection, plant pathogens secrete effector proteins to facilitate colonization. Compared to our knowledge of bacterial effectors, the current understanding of how fungal effectors function is limited. In this study we show that the effector AvrL567-A from the flax rust fungus Melampsora lini interacts with a flax cytosolic cytokinin oxidase, LuCKX1.1 using both yeast-two-hybrid and in planta bimolecular fluorescence assays. Purified LuCKX1.1 protein shows catalytic activity against both N6-(Δ2-isopentenyl)-adenine (iP) and trans-zeatin (tZ) substrates. Incubation of LuCKX1.1 with AvrL567-A results in increased catalytic activity against both substrates. The crystal structure of LuCKX1.1 and docking studies with AvrL567-A indicate that the AvrL567 binding site involves a flexible surface exposed region that surrounds the cytokinin substrate access site, which may explain its effect in modulating LuCKX1.1 activity. Expression of AvrL567-A in transgenic flax plants gave rise to an epinastic leaf phenotype consistent with hormonal effects, although no difference in overall cytokinin levels was observed. We propose that during infection, plant pathogens may differentially modify levels of extracellular and intracellular cytokinins. This article is protected by copyright. All rights reserved.

KEYWORDS:

crystal structure; cytokinin; cytokinin oxidase; flax rust (Melampsora lini) effector; pathogen virulence

PMID:
30242946
DOI:
10.1111/mpp.12749

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