Genetic factors controlling induction of adventitious roots In the Arabidopsis hypocotyl

Adventitious roots (AR) are a special type of roots that by definition do not emerge from other roots, but develop from non-root tissue, such as stems (runners) or any other non-root organ. Adventitious root formation is a key process for vegetative propagation and represents an important step in the commercial production of clonal plants. However, in many species there is no spontaneous root formation and this rooting-recalcitrance is a limiting factor for propagation. The initiation of adventitious roots is dependent on the species and on the type of explants used to study the process. In many cereals for example, adventitious roots are formed at the base of the stem and contribute to a large extent to the regular root structure. Many dicotyledonous plants including Arabidopsis, tomato, mung bean, pine and sunflower show, besides the formation of adventitious root on stem cuttings, the formation of adventitious roots emerging from the hypocotyl. Dark-light transition has been found as a critical condition stimulating AR induction on Arabidopsis etiolated hypocotyls, but little is known about the signaling processes and genetic factors controlling AR induction. Several hormones are involved in adventitious root organogenesis, including auxin, ethylene, jasmonic acid and abscisic acid. In this dissertation we investigated a previously identified small molecule that specifically induces hypocotyl adventitious roots in Arabidopsis thaliana. This molecule named hysparin induces a very high number of ARs on etiolated hypocotyls. Hysparin was used as a tool to study AR formation. Unlike auxins, hysparin does not influence the main root system, including primary root growth and lateral root induction that are similar to non-treated plants. The aim of this PhD study was to unravel signaling components involved in hysparin-mediated AR induction and to determine the physiological parameters influencing de novo root organogenesis