TheAgrobacterium tumefaciensvirulence protein VirE3 is a transcriptional activator of the F-box geneVBF

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During Agrobacterium tumefaciens-mediated transformation of plant cells a part of the tumour-inducing plasmid, T-DNA, is integrated into the host genome. In addition, a number of virulence proteins are translocated into the host cell. The virulence protein VirE3 binds to the Arabidopsis thaliana pBrp protein, a plant-specific general transcription factor of the TFIIB family. To study a possible role for VirE3 in transcriptional regulation, we stably expressed virE3 in A. thaliana under control of a tamoxifen-inducible promoter. By RNA sequencing we showed that upon expression of virE3 the RNA levels of 607 genes were increased more than three-fold and those of 132 genes decreased more than three-fold. One of the strongly activated genes was that encoding VBF (At1G56250), an F-box protein that may affect the levels of the VirE2 and VIP1 proteins. Using Arabidopsis cell suspension protoplasts we showed that VirE3 stimulates the VBF promoter, especially when co-expressed with pBrp. Although pBrp is localized at the external surface of plastids, co-expression of VirE3 and pBrp in Arabidopsis cell suspension protoplasts resulted in the accumulation of pBrp in the nucleus. Our results suggest that VirE3 affects the transcriptional machinery of the host cell to favour the transformation process.

Significance Statement

During Agrobacterium-mediated transformation, T-DNA as well as several virulence proteins are transferred to the plant cell. Here we show that expressing the virulence gene virE3 in Arabidopsis thaliana resulted in translocation of the plant-specific general transcription factor pBrp to the nucleus and subsequent increased transcription of genes including the Arabidopsis F-box protein gene VBF. Our results thus suggest that VirE3 affects the host cell's transcriptional machinery to favour the transformation process.

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