Intersubunit Complementation of Sugar Signal Transduction in VirA Heterodimers and Posttranslational Regulation of VirA Activity in Agrobacterium tumefaciens

AUTOR(ES)

Wise, Arlene A.

FONTE

American Society for Microbiology

RESUMO

The VirA/VirG two-component regulatory system of Agrobacterium tumefaciens regulates expression of the virulence (vir) genes that control the infection process leading to crown gall tumor disease on susceptible plants. VirA, a membrane-bound homodimer, initiates vir gene induction by communicating the presence of molecular signals found at the site of a plant wound through phosphorylation of VirG. Inducing signals include phenols, monosaccharides, and acidic pH. While sugars are not essential for gene induction, their presence greatly increases vir gene expression when levels of the essential phenolic signal are low. Reception of the sugar signal depends on a direct interaction between ChvE, a sugar-binding protein, and VirA. Here we show that the sugar signal received in the periplasmic region of one subunit within a VirA heterodimer can enhance the kinase function of the second subunit. However, sugar enhancement of vir gene expression was vector dependent. virA alleles expressed from pSa-derived vectors inhibited signal transduction by endogenous VirA. Inhibition was conditional, depending on the induction medium and the virA allele tested. Moreover, constitutive expression of virG overcame the inhibitory effect of some but not all virA alleles, suggesting that there may be more than one inhibitory mechanism.

Documentos Relacionados

• Transcriptional regulation of the virA and virG genes of Agrobacterium tumefaciens.
• The VirA protein of Agrobacterium tumefaciens is autophosphorylated and is essential for vir gene regulation.
• Preformed dimeric state of the sensor protein VirA is involved in plant--Agrobacterium signal transduction.
• Phosphorylation of the VirG protein of Agrobacterium tumefaciens by the autophosphorylated VirA protein: essential role in biological activity of VirG.
• Membrane topology and functional analysis of the sensory protein VirA of Agrobacterium tumefaciens.