A 1-phytase type III effector interferes with plant hormone signaling

Doreen Blüher ,Igor Pavlovic ,Oliver Nagel ,Antonia Masch ,Rahel Hinkelmann ,Justin Lee ,Sabine Thieme ,Henning J Jessen ,Gabriel Schaaf ,Debabrata Laha ,Ralf Greiner ,Alexandre Hofer ,Antje Schonsky ,Gerd Ulrich Balcke ,Lennart Eschen‐Lippold ,Nargis Parvin ,Mike Schutkowski ,Alain Tissier ,Jakob Wörner ,Stefan Weber ,Ulla Bonas

doi:10.1038/s41467-017-02195-8

Abstract

Most Gram-negative phytopathogenic bacteria inject type III effector (T3E) proteins into plant cells to manipulate signaling pathways to the pathogen’s benefit. In resistant plants, specialized immune receptors recognize single T3Es or their biochemical activities, thus halting pathogen ingress. However, molecular function and mode of recognition for most T3Es remains elusive. Here, we show that the Xanthomonas T3E XopH possesses phytase activity, i.e., dephosphorylates phytate (myo-inositol-hexakisphosphate, InsP6), the major phosphate storage compound in plants, which is also involved in pathogen defense. A combination of biochemical approaches, including a new NMR-based method to discriminate inositol polyphosphate enantiomers, identifies XopH as a naturally occurring 1-phytase that dephosphorylates InsP6 at C1. Infection of Nicotiana benthamiana and pepper by Xanthomonas results in a XopH-dependent conversion of InsP6 to InsP5. 1-phytase activity is required for XopH-mediated immunity of plants carrying the Bs7 resistance gene, and for induction of jasmonate- and ethylene-responsive genes in N. benthamiana.

Highlights

Most Gram-negative phytopathogenic bacteria inject type III effector (T3E) proteins into plant cells to manipulate signaling pathways to the pathogen’s benefit
While the molecular functions of most T3Es from Xanthomonas are elusive, members of the large family of transcription activatorlike (TAL) effectors act as transcription factors in the plant cell[6]
To unambiguously reveal isomer identity of the XopH cleavage product, we developed a novel method based on nuclear magnetic resonance (NMR) spectroscopy, which can be applied to samples in the presence of buffers and salts that do not interfere with 31P-NMR

Summary

Introduction

Most Gram-negative phytopathogenic bacteria inject type III effector (T3E) proteins into plant cells to manipulate signaling pathways to the pathogen’s benefit. We show that the Xanthomonas T3E XopH possesses phytase activity, i.e., dephosphorylates phytate (myo-inositol-hexakisphosphate, InsP6), the major phosphate storage compound in plants, which is involved in pathogen defense. 5 Department of Stress and Developmental Biology, Leibniz Institute of Plant Biochemistry, Weinberg 3, 06120 Halle (Saale), Germany. 7 Department of Cell and Metabolic Biology, Leibniz Institute of Plant Biochemistry, Weinberg 3, 06120 Halle (Saale), Germany. Single effectors are recognized by specific immune receptors[1] often inducing the hypersensitive response (HR), a rapid, local programmed cell death at the infection site which restricts pathogen ingress[5]. We provide evidence that XopH’s phytase activity is stereoselective for position C1, is required for XopH-dependent HR induction in plants carrying the Bs7 resistance gene and induces the upregulation of hormone-responsive genes

Methods

Results

Conclusion