Auxin control of root development

A plant’s roots system determines both the capacity of a sessile organism to acquire nutrients and water, as well as providing a means to monitor the soil for a range of environmental conditions. Since auxins were first described, there has been a tight connection between this class of hormones and root development. Here we review some of the latest genetic, molecular, and cellular experiments that demonstrate the importance of generating and maintaining auxin gradients during root development. Refinements in the ability to monitor and measure auxin levels in root cells coupled with advances in our understanding of the sources of auxin that contribute to these pools represent important contributions to our understanding of how this class of hormones participates in the control of root development. In addition, we review the role of identified molecular components that convert auxin gradients into local differentiation events, which ultimately defines the root architecture. The early characterization of auxins as “rootforming hormones of plants ” established a long-standing link between this class of small molecules and root development (Went 1929; Thimann and Went 1934). As with the aerial portion of the plant body, a series of iterative modules produces the overall root architecture; the root, which is established during embryo-genesis, gives rise to new lateral roots in a con-tinuous, indeterminate manner. Evidence from many studies highlights the central role of aux-ins in orchestrating the final root architecture. Defining the role of auxins as a component of endogenous developmental programs as well as in mediating environmental stimuli to shape the final root architecture remains at the heart of many active research programs. Here we review some recent discoveries that demonstrate the importance of auxin gradients and the conver-sion of this information into molecular responses that coordinate root development