Hormones and Lateral Root Development

The plant hormone auxin (IAA) has long been known to stimulate lateral root formation and growth. Lateral root development in Arabidopsis has been divided into three general stages - initiation, development and meristem activation - and all three stages are promoted by auxin (Malamy 2005). More recent work with the hormone abscisic acid (ABA) has demonstrated its importance in repressing lateral root development. ABA-deficient plants produce a larger root system than isogenic wildtype plants (Deak and Malamy, 2005), and addition of ABA to a plant's growth medium represses the development of lateral roots (DeSmet et al, 2003). Closer examination revealed that ABA represses the development of lateral root primordia into lateral roots. This has led us to propose a model in which competing ABA and auxin signaling pathways deterrmine the development of the root system. Our current work focuses on understanding the interactions between auxin and ABA.