A single amino-acid substitution allows endo-polygalacturonase of Fusarium verticillioides to acquire recognition by PGIP2 from Phaseolus vulgaris.

Manuel Benedetti,Felice Cervone,Claudia Leggio,Giulia De Lorenzo,Luciano Galantini,Adele Di Matteo,Luca Federici,Nicolae Viorel Pavel,Francesca Sicilia,Federico Andreani,Olga A Zabotina

doi:10.1371/journal.pone.0080610

Manuel Benedetti, Felice Cervone + Show 9 more

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https://doi.org/10.1371/journal.pone.0080610

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Abstract

Polygalacturonases (PGs) are secreted by phytopathogenic fungi to degrade the plant cell wall homogalacturonan during plant infection. To counteract Pgs, plants have evolved polygalacturonase-inhibiting proteins (PGIPs) that slow down fungal infection and defend cell wall integrity. PGIPs favour the accumulation of oligogalacturonides, which are homogalacturonan fragments that act as endogenous elicitors of plant defence responses. We have previously shown that PGIP2 from Phaseolus vulgaris (PvPGIP2) forms a complex with PG from Fusarium phyllophilum (FpPG), hindering the enzyme active site cleft from substrate. Here we analyse by small angle X-ray scattering (SAXS) the interaction between PvPGIP2 and a PG from Colletotrichum lupini (CluPG1). We show a different shape of the PG-PGIP complex, which allows substrate entry and provides a structural explanation for the different inhibition kinetics exhibited by PvPGIP2 towards the two isoenzymes. The analysis of SAXS structures allowed us to investigate the basis of the inability of PG from Fusarium verticilloides (FvPG) to be inhibited by PvPGIP2 or by any other known PGIP. FvPG is 92.5% identical to FpPG, and we show here, by both loss- and gain-of-function mutations, that a single amino acid site acts as a switch for FvPG recognition by PvPGIP2.

Highlights

Pectin is the outer component of the plant cell wall and, is among the first structures to be challenged during pathogen invasion or wounding [1]
We investigated by small angle X-ray scattering (SAXS) analysis the interaction between CluPG1 and FvPGIP2, characterised by a non-competitive inhibition mechanism [33]
previously shown that PGIP2 from Phaseolus vulgaris (PvPGIP2) engages the CluPG1 β-helix with its concave surface and interacts mainly with the C-terminal edge of the enzyme active site cleft, leaving unhampered substrate access

Summary

Introduction

Pectin is the outer component of the plant cell wall and, is among the first structures to be challenged during pathogen invasion or wounding [1]. To counteract PG activity, plants have evolved gene families encoding PG-inhibiting proteins known as PGIPs [8,9]. OGs are among the best-characterized plant damage-associated molecular patterns (DAMPs) [13,14,15,16] and are recognized by receptor proteins belonging to the wall-associated kinase family [17]. PGIP belongs to the extracellular Leucine-Rich Repeat (eLRR) family of proteins [25], like the majority of proteins encoded by the so-called plant resistance (R) genes [12,26]. The isoform 2 of Phaseolus vulgaris (PvPGIP2) is the best characterized inhibitor and has the strongest inhibitory activity against most of the tested PG from different pathogens [23,28]. It has been shown that a few PGIP residues, sometimes only one, are critical for a stable PG-PGIP interaction [27,29]

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