Agrobacterium VirE2 Protein Modulates Plant Gene Expression and Mediates Transformation From Its Location Outside the Nucleus.

Rachelle A Lapham,Esteban Gañán Gómez,Lan-Ying Lee,V M Nivya,Eder Xhako,Stanton B Gelvin

doi:10.3389/fpls.2021.684192

Rachelle A Lapham, Esteban Gañán Gómez + Show 4 more

Open Access

https://doi.org/10.3389/fpls.2021.684192

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Abstract

Agrobacterium effector protein VirE2 is important for plant transformation. VirE2 likely coats transferred DNA (T-DNA) in the plant cell and protects it from degradation. VirE2 localizes to the plant cytoplasm and interacts with several host proteins. Plant-expressed VirE2 can complement a virE2 mutant Agrobacterium strain to support transformation. We investigated whether VirE2 could facilitate transformation from a nuclear location by affixing to it a strong nuclear localization signal (NLS) sequence. Only cytoplasmic-, but not nuclear-localized, VirE2 could stimulate transformation. To investigate the ways VirE2 supports transformation, we generated transgenic Arabidopsis plants containing a virE2 gene under the control of an inducible promoter and performed RNA-seq and proteomic analyses before and after induction. Some differentially expressed plant genes were previously known to facilitate transformation. Knockout mutant lines of some other VirE2 differentially expressed genes showed altered transformation phenotypes. Levels of some proteins known to be important for transformation increased in response to VirE2 induction, but prior to or without induction of their corresponding mRNAs. Overexpression of some other genes whose proteins increased after VirE2 induction resulted in increased transformation susceptibility. We conclude that cytoplasmically localized VirE2 modulates both plant RNA and protein levels to facilitate transformation.

Highlights

Agrobacterium tumefaciens, the causative agent of crown gall disease, transfers virulence effector proteins to infected host plants to facilitate the transfer of T-(transfer) DNA into and trafficking through plant cells
Consistent with data from previous studies (Bhattacharjee et al, 2008; Grange et al, 2008; Lee et al, 2008; Li et al, 2014, 2020; Shi et al, 2014; Li and Pan, 2017; Lapham et al, 2018; Roushan et al, 2018), VirE2-Venus localized to the cytoplasm (Supplementary Figure 1A); VirE2-Venus-nuclear localization signal (NLS) localized to the nucleus (Supplementary Figure 1B)
We have not precisely identified where in the cytoplasm VirE2-Venus localizes, it does not localize to the nucleus, and for convenience we shall hereafter refer to the subcellular localization of VirE2-Venus as “cytoplasmic.”

Summary

Introduction

Agrobacterium tumefaciens, the causative agent of crown gall disease, transfers virulence effector proteins to infected host plants to facilitate the transfer of T-(transfer) DNA into and trafficking through plant cells. Once in the nucleus, transferred DNA (T-DNA) uses the host’s machinery to express transgenes, and may integrate into the host genome. Scientists have used this process to insert beneficial genes into plants by replacing native T-DNA genes with other genes of interest, making Agrobacterium-mediated transformation the preferred method for plant genetic. Expression of VirE2 in the plant can complement a virE2 mutant Agrobacterium strain to full virulence (Citovsky et al, 1992; Simone et al, 2001), suggesting that one of VirE2’s functions in transformation occurs in the plant and involves the maintenance of T-DNA integrity (Gietl et al, 1987; Citovsky et al, 1988)

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