The Transcription Factor Lrp of Pantoea stewartii subsp. stewartii Controls Capsule Production, Motility, and Virulence Important for in planta Growth.

Holly P Bartholomew,Ann M Stevens,Brandi J Thomas,Chastyn Smith,Laura A Giese,David Mackey,Irene N Gentzel,Guadalupe Reynoso,Chase M Mullins

doi:10.3389/fmicb.2021.806504

Holly P Bartholomew, Ann M Stevens + Show 7 more

Open Access

https://doi.org/10.3389/fmicb.2021.806504

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Abstract

The bacterial phytopathogen Pantoea stewartii subsp. stewartii causes leaf blight and Stewart’s wilt disease in susceptible corn varieties. A previous RNA-Seq study examined P. stewartii gene expression patterns during late-stage infection in the xylem, and a Tn-Seq study using a P. stewartii mutant library revealed genes essential for colonization of the xylem. Based on these findings, strains with in-frame chromosomal deletions in the genes encoding seven transcription factors (NsrR, IscR, Nac, Lrp, DSJ_00125, DSJ_03645, and DSJ_18135) and one hypothetical protein (DSJ_21690) were constructed to further evaluate the role of the encoded gene products during in vitro and in planta growth. Assays for capsule production and motility indicate that Lrp plays a role in regulating these two key physiological outputs in vitro. Single infections of each deletion strain into the xylem of corn seedlings determined that Lrp plays a significant role in P. stewartii virulence. In planta xylem competition assays between co-inoculated deletion and the corresponding complementation or wild-type strains as well as in vitro growth curves determined that Lrp controls functions important for P. stewartii colonization and growth in corn plants, whereas IscR may have a more generalized impact on growth. Defining the role of essential transcription factors, such as Lrp, during in planta growth will enable modeling of key components of the P. stewartii regulatory network utilized during growth in corn plants.

Highlights

Pantoea stewartii subsp. stewartii is a bacterial phytopathogen that causes leaf blight and Stewart’s wilt disease when it colonizes the apoplast and xylem of corn, respectively
Among the major virulence components of P. stewartii are the hrp-encoded type III secretion system and the effector WtsE important during both apoplast and xylem infection; a cell wall degrading enzyme (CWDE) thought to be critical for dissemination of P. stewartii throughout the plant and in accessing plant nutrients; and the exopolysaccharide (EPS) capsule produced by P. stewartii in the xylem that affords protection, enables biofilm formation, and is required for the wilt symptoms in infected plants (Bradshaw-Rouse et al, 1981; Coplin and Cook, 1990; Ham et al, 2006; Mohammadi et al, 2012b; Asselin et al, 2015; Doblas-Ibáñez et al, 2019)
Our findings indicate that Lrp is required for the in planta lifestyle of P. stewartii during growth in the xylem

Summary

Introduction

Pantoea stewartii subsp. stewartii is a bacterial phytopathogen that causes leaf blight and Stewart’s wilt disease when it colonizes the apoplast and xylem of corn, respectively. The bacterium is Pantoea stewartii Transcription Factors enteric within the beetle, but it is transferred into the apoplast of the corn leaves during insect feeding. Other known virulence factors include capsule pigment, surface motility and adhesins, siderophore production, an RTX toxin, oxidative stress regulation with OxyR and SoxR, outer membrane porins, and Lon protease (Mohammadi et al, 2012a; Burbank et al, 2014; Burbank and Roper, 2014; Kernell Burke et al, 2015; Roper et al, 2015; Duong et al, 2018). Regulation of the bacterium’s transition from the apoplast to the xylem is in large part controlled by a quorum sensing (QS) system, where cell–cell signaling of high cell densities leads to a decrease in motility and an increase in capsule production (Koutsoudis et al, 2006)

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