Bacteria use plant defence for genetic modification - new perspective in GMO debate
Genetically modified organisms (GMOs) are set to play an important role in future food and fuel production (previous post). The father of the technique of genetically modifying crops, Marc Van Montagu, for example, is a staunch supporter of such plants, because they can improve yields, end hunger in developing countries and unlock a vast potential for the production of sustainable biofuels and bioproducts that allow us to fight climate change (more here). But transgenic crops and GMOs used for bioconversion remain highly controversial, especially in Europe. Scientists from the continent now describe an entirely natural process occuring in plant cells that is similar to how genomes are artificially modified in engineered crops. Their findings, published today in Science, may offer a new perspective in the debate over GMOs.
Bacteria that cause tumours in plants modify plant genomes by skilfully exploiting the plants' first line of defence. Utilising the plant's own proteins, bacterial genes infiltrate first the nucleus then the plant genome, where they reprogramme the plant's metabolism to suit their own needs. This process was recently discovered as part of an Austrian Science Fund FWF project.
The genetic manipulation of plants is both a subject of great controversy in Europe and a tactic already practiced by certain bacteria. The soil bacterium known as crown-gall bacterium (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 bacteria genes infiltrate the cell's nucleus - particularly as the defence mechanisms of plant cells react so rapidly to bacterial invasion.
A surprising detail of this process has now been uncovered by the team of Prof. Heribert Hirt working at the Max F. Perutz Laboratories at the University of Vienna and the URGV Plant Genomics Institute near Paris which Hirt joined as future director earlier this year. VIP1, a plant cell protein, 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. Hirt explains: "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." Hirt compares this strategy, which inevitably means that the plants own defences cause its downfall, to the famous Trojan Horse:
energy :: sustainability :: biomass :: bioenergy :: biofuels :: energy crops :: genetically modified organism :: plant biology ::
The scientist explains further that plants have an immune defence 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. These are enzymes that regulate the activity of other proteins by adding phosphate groups to them. 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 defence genes there.
The following model illustrates the early processes in an infected plant cell. The invasion of T-DNA and the identification of the bacterium as an invader occur simultaneously. While protein kinases phosphorylate VIP1 in the cytoplasm, the bacterial T-DNA adheres to VIP1, thereby enabling it to infiltrate the nucleus unnoticed. The result is the joint infiltration of both friend and foe. Once inside the nucleus, the T-DNA is inserted into the plant genome and the process of tumour formation begins while the activated defence genes simultaneously organise the plant cell's defence mechanisms. It is too late though - the cell has already been transformed.
The fact that genetic modifications occur continuously in nature in this way offers a new angle to look at the controversies over transgenic crops.
References:
Armin Djamei, Andrea Pitzschke, Hirofumi Nakagami, Iva Rajh, Heribert Hirt, "Trojan horse strategy in Agrobacterium transformation - Abusing MAPK-targeted VIP1 defence signalling" , Science, 318, 453 (2007).
Austrian Science Fund FWF: Bacteria Use Plant Defence for Genetic Modification - October 19, 2007.
Biopact: Marc Van Montagu and GM energy crops - July 05, 2007
Article continues
Bacteria that cause tumours in plants modify plant genomes by skilfully exploiting the plants' first line of defence. Utilising the plant's own proteins, bacterial genes infiltrate first the nucleus then the plant genome, where they reprogramme the plant's metabolism to suit their own needs. This process was recently discovered as part of an Austrian Science Fund FWF project.
The genetic manipulation of plants is both a subject of great controversy in Europe and a tactic already practiced by certain bacteria. The soil bacterium known as crown-gall bacterium (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 bacteria genes infiltrate the cell's nucleus - particularly as the defence mechanisms of plant cells react so rapidly to bacterial invasion.
A surprising detail of this process has now been uncovered by the team of Prof. Heribert Hirt working at the Max F. Perutz Laboratories at the University of Vienna and the URGV Plant Genomics Institute near Paris which Hirt joined as future director earlier this year. VIP1, a plant cell protein, 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. Hirt explains: "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." Hirt compares this strategy, which inevitably means that the plants own defences cause its downfall, to the famous Trojan Horse:
energy :: sustainability :: biomass :: bioenergy :: biofuels :: energy crops :: genetically modified organism :: plant biology ::
The scientist explains further that plants have an immune defence 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. These are enzymes that regulate the activity of other proteins by adding phosphate groups to them. 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 defence genes there.
The following model illustrates the early processes in an infected plant cell. The invasion of T-DNA and the identification of the bacterium as an invader occur simultaneously. While protein kinases phosphorylate VIP1 in the cytoplasm, the bacterial T-DNA adheres to VIP1, thereby enabling it to infiltrate the nucleus unnoticed. The result is the joint infiltration of both friend and foe. Once inside the nucleus, the T-DNA is inserted into the plant genome and the process of tumour formation begins while the activated defence genes simultaneously organise the plant cell's defence mechanisms. It is too late though - the cell has already been transformed.
The fact that genetic modifications occur continuously in nature in this way offers a new angle to look at the controversies over transgenic crops.
References:
Armin Djamei, Andrea Pitzschke, Hirofumi Nakagami, Iva Rajh, Heribert Hirt, "Trojan horse strategy in Agrobacterium transformation - Abusing MAPK-targeted VIP1 defence signalling" , Science, 318, 453 (2007).
Austrian Science Fund FWF: Bacteria Use Plant Defence for Genetic Modification - October 19, 2007.
Biopact: Marc Van Montagu and GM energy crops - July 05, 2007
Article continues
Friday, October 19, 2007
Microbes share out carbon in the roots of plants, play key role in the carbon cycle
The green leaves of plants use the energy of sunlight to make sugar by combining water with carbon dioxide from the atmosphere. This sugar fuels the plant’s growth, but scientists in the University’s Department of Biology discovered that some of it goes straight to the roots to feed a surprising variety of microbes.
A study led by Professor Peter Young, of the Department of Biology at York and Dr Philippe Vandenkoornhuyse of the University of Rennes in France is published in the latest issue of the Proceedings of the National Academy of Sciences of the USA (PNAS).
In the carbon cycle, plants remove the main greenhouse gas - carbon dioxide - from the atmosphere. Eventually, the carbon compounds that plants make are 'eaten' by microbes and animals or used as fuels by humans, which release carbon dioxide back into the atmosphere. The rapid cycling by microbes demonstrated by the new research is an important link in this process.
The researchers traced the path of the carbon by replacing the normal carbon dioxide in the air around the plants with a version made with C-13, a natural, non-radioactive form of carbon that is slightly heavier than the usual kind. Within hours, microbes in the roots were feeding on sugars laden with C-13 and using it to build their own cells.
The newly-made molecules of DNA and RNA produced by the microbes could be separated from pre-existing ones because the C13 made them heavier. DNA and RNA are large molecules that carry genetic information about the organisms that made them, so it was possible to identify the microbes that made those heavy molecules. These were the “greedy” ones that were consuming the largest share of the sugars provided by the plant:
energy :: sustainability :: biomass :: bioenergy :: biofuels :: carbon dioxide :: carbon cycle :: microbes :: soil :: symbiosis ::
The researchers found a high diversity of both types of microbe inside the roots of grass or clover plants growing in a pasture, but the “heavy” label revealed that some of these were growing much more actively than others.
Professor Young says it is these active organisms that are important because they are turning sugar back into carbon dioxide, which is released into the atmosphere. The researchers were astonished at the wide variety of active bacteria that they discovered. Many of them had not been seen in plant roots before, and the scientists admit they have no idea how they may affect plant growth.
The role of mycorrhizal fungi (image, click to enlarge) is better known. They are particularly important in carbon cycling, because they pump the carbon compounds out of the root into a massive network of fine fungal filaments in the soil, where it becomes available to other microbes and also to larger soil organisms like worms, mites and insects. In return, the fungus gathers phosphorus from the soil and delivers it to the plant, helping the plant to grow better. The research confirmed that there were many different fungi in the roots of each plant, but revealed, for the first time, which of these fungi were most active.
Picture: the tiny filaments of mycorrhizal fungi extending from a plant's roots illustrate a symbiotic relationship, increasing a plant's ability to collect moisture and nutrients, and playing a key role in the carbon cycle.
References:
Philippe Vandenkoornhuyse, et. al. "Active root-inhabiting microbes identified by rapid incorporation of plant-derived carbon into RNA", Published online before print October 15, 2007, Proc. Natl. Acad. Sci. USA, 10.1073/pnas.0705902104
University of York: Hungry microbes share out the carbon in the roots of plants - October 18, 2007.
Article continues
posted by Biopact team at 7:10 PM 0 comments links to this post