Molecular interaction between Agrobacterium and plant cells

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Crown gall tumor is incited on dicotyledonous plants by infection with Agrobacterium tumefaciens harboring Ti plasmid. Upon infection, expression of most of vir genes on the Ti plasmid is induced or enhanced in the bacterial cells.Some of the vir gene products are involved in transfer of T-DNA which is transferred. We have previously found that monosaccharides such as glucose and galactose can enhance signals initiated by plant phenolic compounds. In the present study, we demonstrated that the signal by such monosaccharides is transduced into cytoplasm through the sensor protein VirA.In addition, the periplasmic domain of VirA was shown to be responsible for signal perception by the sugars and the linker domain and the region of the C-terminal side of the TM2 domain are shown to be involved in signaling of phenolics. In addition to these investigations, we have examined whether infection of plants with Agrobacterium cells activates a certain protein kinase. Our results showed that a novel protein kinase which has molecular mass of 46 kDa was transiently activated by infection of leaf discs of tobacco. Activities of 46-kDa kinases were detected in a wide variety of plant species after wounding, indicating that this protein kinase is present in a number of plants. It should be important to investigate physiological relationship between infection with Agrobacterium and function of this kinase.