The Novel Cyst Nematode Effector Protein 19C07 Interacts with the Arabidopsis Auxin Influx Transporter LAX3 to Control Feeding Site Development

Chris Lee,Tarek Hewezi,Eric L Davis,Melissa G Mitchum,Malcolm Bennett,Thomas J Baum,Charlotte Kenning,Benjamin Peret,Richard Hussey,Demosthenis Chronis

doi:10.1104/pp.110.167197

Abstract

Plant-parasitic cyst nematodes penetrate plant roots and transform cells near the vasculature into specialized feeding sites called syncytia. Syncytia form by incorporating neighboring cells into a single fused cell by cell wall dissolution. This process is initiated via injection of esophageal gland cell effector proteins from the nematode stylet into the host cell. Once inside the cell, these proteins may interact with host proteins that regulate the phytohormone auxin, as cellular concentrations of auxin increase in developing syncytia. Soybean cyst nematode (Heterodera glycines) Hg19C07 is a novel effector protein expressed specifically in the dorsal gland cell during nematode parasitism. Here, we describe its ortholog in the beet cyst nematode (Heterodera schachtii), Hs19C07. We demonstrate that Hs19C07 interacts with the Arabidopsis (Arabidopsis thaliana) auxin influx transporter LAX3. LAX3 is expressed in cells overlying lateral root primordia, providing auxin signaling that triggers the expression of cell wall-modifying enzymes, allowing lateral roots to emerge. We found that LAX3 and polygalacturonase, a LAX3-induced cell wall-modifying enzyme, are expressed in the developing syncytium and in cells to be incorporated into the syncytium. We observed no decrease in H. schachtii infectivity in aux1 and lax3 single mutants. However, a decrease was observed in both the aux1lax3 double mutant and the aux1lax1lax2lax3 quadruple mutant. In addition, ectopic expression of 19C07 was found to speed up lateral root emergence. We propose that Hs19C07 most likely increases LAX3-mediated auxin influx and may provide a mechanism for cyst nematodes to modulate auxin flow into root cells, stimulating cell wall hydrolysis for syncytium development.

Highlights

Plant-parasitic cyst nematodes penetrate plant roots and transform cells near the vasculature into specialized feeding sites called syncytia
We report the results of a yeast two-hybrid approach that identified the Arabidopsis auxin influx transporter LAX3 as a potential interactor with the Hs19C07 effector protein
An in situ analysis demonstrated that Hg19C07 mRNA is induced only upon the onset of parasitism and is present exclusively inside of the single dorsal esophageal gland cell in both early-stage (Fig. 1B; parasitic second-stage juveniles [pJ2]) and late-stage (Fig. 1C; parasitic fourth-stage juveniles [pJ4]) nematodes, indicating that Hs19C07 is a secreted protein from the dorsal esophageal gland cell expressed during parasitism

Summary

Introduction

Plant-parasitic cyst nematodes penetrate plant roots and transform cells near the vasculature into specialized feeding sites called syncytia. Cyst nematodes may manipulate auxin flow through the developing feeding site, as the Arabidopsis auxin influx transport protein, AUX1, is transcriptionally up-regulated in developing feeding sites (Mazarei et al, 2003) and the auxin efflux transporter, PIN3, relocalizes to the lateral plasma membrane of the developing syncytium (Grunewald et al, 2009a). Treatment with a polar auxin transport inhibitor, N-1-naphthylphthalamic acid, delays nematode development and inhibits nematode feeding site formation (Goverse et al, 2000) Taken together, these findings suggest a model in which an accumulation of auxin in the developing syncytium plays a substantive role in the formation of cyst nematode feeding sites from existing root cells

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