Role of Exopolygalacturonase-Related Genes in Potato-Verticillium dahliae Interaction.

Xiaohan Zhu,Mohammad Sayari,Fouad Daayf

doi:10.3390/pathogens10060642

Xiaohan Zhu, Mohammad Sayari + Show 1 more

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https://doi.org/10.3390/pathogens10060642

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Abstract

Verticillium dahliae is a hemibiotrophic pathogen responsible for great losses in dicot crop production. An ExoPG gene (VDAG_03463,) identified using subtractive hybridization/cDNA-AFLP, showed higher expression levels in highly aggressive than in weakly aggressive V. dahliae isolates. We used a vector-free split-marker recombination method with PEG-mediated protoplast to delete the ExoPG gene in V. dahliae. This is the first instance of using this method for V. dahliae transformation. Only two PCR steps and one transformation step were required, markedly reducing the necessary time for gene deletion. Six mutants were identified. ExoPG expressed more in the highly aggressive than in the weakly aggressive isolate in response to potato leaf and stem extracts. Its expression increased in both isolates during infection, with higher levels in the highly aggressive isolate at early infection stages. The disruption of ExoPG did not influence virulence, nor did it affect total exopolygalacturonase activity in V. dahliae. Full genome analysis showed 8 more genes related to polygalacturonase/pectinase activity in V. dahliae. Transcripts of PGA increased in the △exopg mutant in response to potato leaf extracts, compared to the wild type. The expression pattern of those eight genes showed similar trends in the △exopg mutant and in the weakly aggressive isolate in response to potato extracts, but without the increase of PGA in the weakly aggressive isolate to leaf extracts. This indicated that the △exopg mutant of V. dahliae compensated by the suppression of ExoPG by activating other related gene.

Highlights

Verticillium dahliae is a hemibiotrophic pathogen that causes wilt symptoms and results in great losses in a wide range of dicot hosts [1], including in important economic crops [2]
Genetic resistance has not been very useful so far, i.e., tomato lines contain the Ve resistance gene, it only has resistance to V. dahliae race 1 [8,9], and cultivars with effective resistance have not been developed in the majority of the crops at risk
Glycosidic bonds of polysaccharides can be cut by enzymes belonging to the glycoside-hydrolases (GH) family [11]. Polygalacturonases belong to these pectin-degrading enzymes, which include both endopolygalacturonases (EndoPGs) and exopolygalacturonases (ExoPGs)

Summary

Introduction

Verticillium dahliae is a hemibiotrophic pathogen that causes wilt symptoms and results in great losses in a wide range of dicot hosts [1], including in important economic crops [2]. The plant cell wall is a key barrier of protection from pathogen attacks It consists primarily of cuticular wax, cutin, glycans, cellulose, pectic substances, and cell wall structural proteins [10]. EndoPGs hydrolyze the polysaccharide randomly to produce oligogalacturonides, while ExoPGs hydrolyze the polymer from the non-reducing end to produce a single galacturonic acid [12,13]. Both the EndoPGs and ExoPGs belong to the GH28 family [12]

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