Genes regulating root system architecture

How roots explore their soil environment determines their ability to acquire nutrients and water. Very few genes controlling root system architecture (RSA) are known, primarily because of the difficulty of observing root growth in soil. Initially, we reduced the complexity of the growth environment to a gel matrix, which would maintain the three-dimensional structure of the root. In collaboration with Joshua Weitz (Georgia Tech) and Herbert Edelsbrunner (IST Austria) we developed image analysis and 3-D reconstruction software. Analysis of a set of recombinant inbred lines (RILs) allowed us to map QTLs for root architecture traits in rice and maize. To explore how these traits respond to soil, we grew rice plants in media consisting of three different particle sizes. Using x-ray imaging in collaboration with Dan Goldman (Georgia Tech) we found some subspecies had little response, while others changed their growth pattern dramatically.

Darwin was fascinated by plant movements and found evidence that roots moved in a circular pattern through soil. This process, which he called circumnutation has not received much attention, probably due to the difficulty of studying movement in soil. We have identified a rice mutant that is unable to perform circumnutation, which allowed us to determine a genetic pathway underlying this process as well as discover a soil exploration process that is greatly facilitated by it.