The effector repertoire of Fusarium oxysporum determines the tomato xylem proteome composition following infection.

Fleur Gawehns,Oskar Bruning,Sjef Boeren,Lisong Ma,Petra M. Houterman,Ben J. C. Cornelissen,Martijn Rep,Frank L. W. Takken

doi:10.3389/fpls.2015.00967

Fleur Gawehns, Oskar Bruning + Show 6 more

Open Access

https://doi.org/10.3389/fpls.2015.00967

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Abstract

Plant pathogens secrete small proteins, of which some are effectors that promote infection. During colonization of the tomato xylem vessels the fungus Fusarium oxysporum f.sp. lycopersici (Fol) secretes small proteins that are referred to as SIX (Secreted In Xylem) proteins. Of these, Six1 (Avr3), Six3 (Avr2), Six5, and Six6 are required for full virulence, denoting them as effectors. To investigate their activities in the plant, the xylem sap proteome of plants inoculated with Fol wild-type or either AVR2, AVR3, SIX2, SIX5, or SIX6 knockout strains was analyzed with nano-Liquid Chromatography-Mass Spectrometry (nLC-MSMS). Compared to mock-inoculated sap 12 additional plant proteins appeared while 45 proteins were no longer detectable in the xylem sap of Fol-infected plants. Of the 285 proteins found in both uninfected and infected plants the abundance of 258 proteins changed significantly following infection. The xylem sap proteome of plants infected with four Fol effector knockout strains differed significantly from plants infected with wild-type Fol, while that of the SIX2-knockout inoculated plants remained unchanged. Besides an altered abundance of a core set of 24 differentially accumulated proteins (DAPs), each of the four effector knockout strains affected specifically the abundance of a subset of DAPs. Hence, Fol effectors have both unique and shared effects on the composition of the tomato xylem sap proteome.

Highlights

Pathogens such as bacteria, fungi, oomycetes, protozoa and nematodes continuously challenge the plant immune system
The 29 specific differentially accumulated proteins (DAPs), and the 15 DAPs (Solyc12g099160.1.1, Solyc11g040330.1.1, Solyc10g074820.1.1, Solyc09g007520.1.1, Solyc06g072230.1.1, Solyc01g108840.1.1, Solyc09g007010.1.1, Solyc08g066810.1.1, Solyc06g072220.1.1, Solyc05g054710.1.1, Solyc05g052280.1.1, Solyc04g072000.1.1, Solyc02g077040.1.1, Solyc02g024050.1.1, and Solyc01g105070.1.1) whose abundance was either increased or decreased in the xylem sap of Fol SIX6 knockout compared to other effector knockout strains inoculated tomato plants (Table 2, Figure 6A) distribute over all Gene Ontology (GO) categories except “others.” Relatively more DAPs belonging to the categories “protein modification and degradation” and “redox” were identified than in Fol007 vs. mock (Figure 6B) and relatively fewer proteins from “stress responses,” “peroxidases,” and “cell wall.”
When focusing on Experiment 1, 12 new tomato proteins were found while 45 proteins were no longer detected in the xylem sap proteome as compared to mock-infected plants

Summary

INTRODUCTION

Fungi, oomycetes, protozoa and nematodes continuously challenge the plant immune system. In response to Fol infection the abundance of specific tomato proteins, including PR proteins, changes in the xylem sap (Rep et al, 2002; Houterman et al, 2007). Each effector is expected to affect only a specific subset of plant responses To test this hypothesis and to gain insight into these functions, we here set out to determine the changes in the xylem sap proteome following Fol infection using a label-free quantitative, large-scale proteomics approach. A specific effect of Fol effectors on the xylem sap composition was revealed, and a common one implying that effector proteins exert non-redundant activities and have shared functions

MATERIALS AND METHODS

Findings

DISCUSSION