Structural and functional insights into the modulation of the activity of a flax cytokinin oxidase by flax rust effector AvrL567‐A

• Published in: Molecular plant pathology Vol. 20; no. 2; pp. 211 - 222
• Main Authors: Wan, Li, Koeck, Markus, Williams, Simon J., Ashton, Anthony R., Lawrence, Gregory J., Sakakibara, Hitoshi, Kojima, Mikiko, Böttcher, Christine, Ericsson, Daniel J., Hardham, Adrienne R., Jones, David A., Ellis, Jeffrey G., Kobe, Bostjan, Dodds, Peter N.
• Format: Journal Article
• Language: English
• Published: England John Wiley & Sons, Inc 01.02.2019; John Wiley and Sons Inc
• Subjects: Adenine; Analysis; Basidiomycota - genetics; Basidiomycota - metabolism; Basidiomycota - pathogenicity; Binding sites; Catalysis; Catalytic activity; Colonization; Crystal structure; Crystals; cytokinin; cytokinin oxidase; Cytokinins; Docking; Effectors; Flax; Flax - metabolism; Flax - microbiology; flax rust (Melampsora lini) effector; Fluorescence; Fungal Proteins - genetics; Fungal Proteins - metabolism; Genetic engineering; Health aspects; Hormonal effects; Infections; Original; Oxidase; Oxidases; Oxidoreductases - genetics; Oxidoreductases - metabolism; pathogen virulence; Pathogens; Phenotypes; Plant Diseases - microbiology; Plant Proteins - genetics; Plant Proteins - metabolism; Plants; Protein Binding; Proteins; Rust fungi; Structure; Structure-function relationships; Substrates; Transgenic plants; Two-Hybrid System Techniques; Yeast; Zeatin; crystal structure; cytokinin oxidase; cytokinin; pathogen virulence; flax rust (Melampsora lini) effector
• ISSN: 1464-6722; 1364-3703
• DOI: 10.1111/mpp.12749

Summary During infection, plant pathogens secrete effector proteins to facilitate colonization. In comparison with 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 (2iP) 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 the levels of extracellular and intracellular cytokinins.