F-Box Gene D5RF Is Regulated by Agrobacterium Virulence Protein VirD5 and Essential for Agrobacterium-Mediated Plant Transformation.

We previously reported that theAgrobacteriumvirulence protein VirD5 possesses transcriptional activation activity, binds to a specific DNA element D5RE, and is required forAgrobacterium-mediated stable transformation, but not for transient transformation. However, direct evidence for a role of VirD5 in plant transcriptional regulation has been lacking. In this study, we found that the Arabidopsis geneD5RF(coding for VirD5 response F-box protein,At3G49480) is regulated by VirD5.D5RFhas two alternative transcripts of 930 bp and 1594 bp that encode F-box proteins of 309 and 449 amino acids, designated as D5RF.1 and D5RF.2, respectively. D5RF.2 has a N-terminal extension of 140 amino acids compared to D5RF.1, and both of them are located in the plant cell nucleus. The promoter of theD5RF.1contains two D5RE elements and can be activated by VirD5. The expression of D5RF is downregulated when the host plant is infected withvirD5deletedAgrobacterium. Similar to VirD5, D5RF also affects the stable but not transient transformation efficiency ofAgrobacterium. Some pathogen-responsive genes are downregulated in thed5rfmutant. In conclusion, this study further confirmedAgrobacteriumVirD5 as the plant transcription activator and identifiedArabidopsis thalianaD5RF.1as the first target gene of VirD5 in regulation.