A group of researchers literally watched meristem genes turn on and off in a cyclical fashion in the developing roots of higher plants, such as conifers and ferns, according to a study published in Science today (10th September). This oscillating expression, they say, is how these plants form their complex root systems. As the root meristem grows downward into the soil, it produces undifferentiated cells that, once assigned their function, will form the intricate root system of the plant. What type of root the cells become is determined in an area a fixed distance behind the growing root tip called the "oscillation zone", where specific genes in the cells turn on and off like clockwork. Depending on which genes are on and which are off when the "oscillation zone" passes through determines the cells' capacity for producing lateral roots, which anchor the plant firmly into the soil and facilitate water uptake and the extraction of nutrients. Previous studies suggested levels of the plant hormone auxin mirrored this oscillating gene expression and could be useful in predicting the locations of lateral branching. In an attempt to demystify the mechanism underlying the development of plant roots, linkurl:Philip Benfey;http://www.biology.duke.edu/benfeylab/index.htm of Duke University and his team paired the promoter DR5, a gene that can sense changes in auxin levels, with the luciferase gene, which illuminates when activated, to follow gene expression in Arabidopsis plants in real time. Every six hours the expression of DR5 pulsed like a lighthouse. At each location the light pulsed, a lateral root was later observed branching off the primary root. Auxin may not fully explain the changes in DR5 expression, however, and further studies are needed to understand the observed fluctuations in DR5 and how they are related to auxin and root development. Video copyright Science/AAAS
Video copyright Science/AAAS
