Toward understanding the genetic network controlling maize root architecture

The root system in maize is characterized by different root types, each of which contributes to the development and establishment of the plants in a distinctive manner. During very early development, the embryonic primary and seminal roots are predominant, together with their post-embryonic lateral roots. Shoot-borne roots are formed at each consecutive node of the shoot and are called crown roots when they grow on nodes that reside under the soil line, and brace roots when growing from above ground nodes. In our group we are interested in the genetic mechanism underlying root formation and we take a forward genetics approach to identify genes involved in the molecular pathways that drive maize root development. Several monogenic root mutants have been selected for our map-based cloning activities. Two of them control crown and brace root formation. The rt1 (rootless1) mutant has a variable number of crown roots in the first two nodes, but misses all shoot-borne roots at the higher nodes. In contrast, the rtcs (rootless concerning crown and seminal roots) mutant was identified because it lacks the embryonically formed seminal roots and post-embryonically formed shoot-borne roots. Other two mutants we are studying control lateral root formation at the seedling level, in the primary root. Among them, the recently characterized rum1 (rootless with undetectable meristems 1) mutant is defective in both the initiation of lateral roots from the primary root, and the initiation of seminal roots. Here, we present data of the strategy we developed for the positional cloning and characterization of two of the maize genes controlling root formation: the RTCS gene, which encodes for a LOB domain protein, and the RUM1 gene, which encodes for a member of the AUX/IAA gene family involved in auxin signalling. (author)