Bacteria Use Plant Defense for Genetic Manipulation
The genetic manipulation of plants is both a subject of great controversy in certain areas and a tactic already practiced by certain bacteria. The bacterium known as crown-gall (Agrobacterium) manipulates the genetic make-up of plants by inserting its own DNA into the nuclei and, consequently, into the genetic material of the plant cells. The genetically modified plants are then reprogrammed to ensure uninhibited cell division and produce nutrients to feed the bacteria. What was not previously understood is exactly how bacterial genes infiltrate the cell's nucleus - particularly as the defense mechanisms of plant cells react so rapidly to bacterial invasion.
A surprising detail of this process has now been uncovered by the team working at the Max F. Perutz Laboratories at the University of Vienna and the URGV Plant Genomics Institute near Paris. The plant cell protein VIP1 is at the heart of their research. It was already known that this protein supports the transport of bacterial DNA known as T-DNA into the nucleus, and yet the exact role of VIP1 was unclear. Prof. Heribert Hirt of the team explains that “We were able to show that VIP1 is a protein that regulates various genes designed to defend against bacterial invasion. However, VIP1 only occurs initially in the cytoplasm of cells and - in order to fulfil its role as a regulator - it then needs to migrate into the nucleus. It is precisely this movement that the bacterium exploits in order to inject its T-DNA into the nucleus.”
Prof. Hirt explains further - “Plants have an immune defense mechanism that is triggered when the plant detects certain molecules of the invader and works by activating genes in the nucleus.” Once the invader has been detected, specific protein kinases in the cytoplasm are activated. One of the proteins phosphorylated by these protein kinases is VIP1, which is only granted access to the nucleus after this phosphorylation, so that it can activate the relevant defense genes there. While protein kinases phosphorylate VIP1 in the cytoplasm, the bacterial T-DNA adheres to VIP1, thereby enabling it to infiltrate the nucleus unnoticed. Once inside the nucleus, the T-DNA is inserted into the plant genome and the process of tumor formation begins while the activated defense genes simultaneously organize the plant cell's defense mechanisms. It is too late though - the cell has already been transformed. (Science Daily, 10/29/07).
