An international team of researchers has pinpointed a gene in plants that plays a key role in the development of root offshoots. The discovery has important implications for plant breeding and may ultimately lead to more environmentally friendly agricultural systems and the production of better crops. It might even have some importance with a view to stem cell and cancer research in animals, the scientists report in renowned journal Science. Analysing the mechanism in the commonly used model plant Arabidopsis thaliana, or mouse-ear cress, the scientists from Belgium, Germany, the UK and the US identified the gene ARABIDOPSIS CRINKLY4 (ACR4) as the most likely candidate to determine which cells will produce offshoots. ACR4 produces the ACR4 protein, which is frequently found on the outside of cells. The protein acts as a receptor for signals from the outside, i.e. the surrounding soil, and transmits them to the controlling mechanisms on the inside of the cell. To confirm that they were on the right track, the researchers disrupted the function of the ACR4 gene. When they did this, the creation of offshoots was disturbed. Root offshoots are generated from stem cells found inside the root. These stem cells undergo asymmetric cell division: contrary to usual cell division, which produces two identical cells, asymmetric cell division - as the name indicates - generates two different cells. One cell is identical to the original stem cell and retains is pluripotency, while the other becomes a specialised cell, namely a secondary root cell. It was this particular mechanism of asymmetric cell division, which was disrupted when ACR4 was switched off. Understanding this process, it will now be possible to promote or slow down the formation of root offshoots, the scientists say. Both strategies have their merit in agriculture, since the root system is a determining factor in the growth and health of plants: an extensive root system helps a plant absorb nutrients and fluids from the surrounding soil. As a result, not only will such plants need less fertiliser and grow more easily in dry or infertile soils, but they will also be anchored more firmly in the soil, thus counteracting soil erosion. Slowing down secondary root formation, on the other hand, could be a strategy to keep plants like potatoes and sugar beets from putting too much energy into offshoots and make them invest it in the production of nutrients. At the same time, a less extensive root system will make such plants easier to harvest. Furthermore, the finding might also contribute to stem cell and cancer research in animals, as similar mechanisms might underlie the specialisation of stem cells and irregular cell division in both animals and plants. 'Plants and animals require asymmetric cell division, coinciding with the acquisition of the correct cell fate, growth and reproduction,' the scientists write in Science. 'For instance, the asymmetric cell division mechanism is central to the activity of stem cells, and recent studies have shown a correlation with cancer-like states of the cell when asymmetric cell divisions do not take place.'
Belgium, Germany, United States