Genome-Wide Identification of Dickeya solani Transcriptional Units Up-Regulated in Response to Plant Tissues From a Crop-Host Solanum tuberosum and a Weed-Host Solanum dulcamara.

Robert Czajkowski,Jakub Fikowicz-Krosko,Nicole Hugouvieux-Cotte-Pattat,Lukasz Rabalski,Marta Krychowiak-Maśnicka,Tomasz Maciag,Malwina Richert,Sylwia Jafra,Paulina Czaplewska

doi:10.3389/fpls.2020.580330

Abstract

Dickeya solani is a Gram-negative bacterium able to cause disease symptoms on a variety of crop and ornamental plants worldwide. Weeds including Solanum dulcamara (bittersweet nightshade) growing near agricultural fields have been reported to support populations of soft rot bacteria in natural settings. However, little is known about the specific interaction of D. solani with such weed plants that may contribute to its success as an agricultural pathogen. The aim of this work was to assess the interaction of D. solani with its crop plant (Solanum tuberosum) and an alternative (S. dulcamara) host plant. From a collection of 10,000 Tn5 transposon mutants of D. solani IPO2222 carrying an inducible, promotorless gusA reporter gene, 210 were identified that exhibited plant tissue-dependent expression of the gene/operon into which the Tn5 insertion had occurred. Thirteen Tn5 mutants exhibiting the greatest plant tissue induction of such transcriptional units in S. tuberosum or S. dulcamara as measured by qRT-PCR were assessed for plant host colonization, virulence, and ability to macerate plant tissue, as well as phenotypes likely to contribute to the ecological fitness of D. solani, including growth rate, carbon and nitrogen source utilization, motility, chemotaxis toward plant extracts, biofilm formation, growth under anaerobic conditions and quorum sensing. These 13 transcriptional units encode proteins involved in bacterial interactions with plants, with functions linked to cell envelope structure, chemotaxis and carbon metabolism. The selected 13 genes/operons were differentially expressed in, and thus contributed preferentially to D. solani fitness in potato and/or S. dulcamara stem, leaf, and root tissues.

Highlights

Soft Rot Pectobacteriaceae (SRP: Pectobacterium spp. and Dickeya spp.) are important, broad host range phytopathogenic, necrotrophic bacteria that cause substantial and increasing economic losses in agricultural crops worldwide (Toth et al, 2003; Charkowski, 2018)
There is only limited information concerning the colonization of potato, the primary host of D. solani (Czajkowski et al, 2010a; Czajkowski et al, 2010b), and there is little information present in the literature of how the bacterium interacts with alternative hosts (Ma et al, 2007)
We examined the hypothesis that the initial host recognition step is crucial for D. solani to differentiate between primary and alternative plant hosts during infection

Summary

Introduction

Soft Rot Pectobacteriaceae (SRP: Pectobacterium spp. and Dickeya spp.) are important, broad host range phytopathogenic, necrotrophic bacteria that cause substantial and increasing economic losses in agricultural crops worldwide (Toth et al, 2003; Charkowski, 2018). A relatively high incidence of SRPcaused diseases is observed in potato fields even after planting pathogen-free seed tubers (Toth et al, 2011) In these cases, the rapid development of blackleg and soft rot symptoms cannot be explained by latent infections of planting material (van der Wolf and de Boer, 2007). Such observations suggest that SRP may overwinter in soil in association with various plants, primarily in protected locations in the roots of alternative host plants and/or on or within volunteer crop plants from previous plantings (Pérombelon, 1992)

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