By analogy to their animal counterparts, plant hormones were originally recognized as regulators of growth and development (van Overbeek, 1966; Galston and Davies, 1969; Santner and Estelle, 2009). They have subsequently been demonstrated to achieve this by modulating both processes in response to both intrinsic and environmental cues (Wolters and Jurgens, 2009). Accordingly it is currently accepted that hormones not only exert intrinsic growth control but also mediate adaptation of plant development to transiently changing conditions (Wolters and Jurgens, 2009). Equally accepted is the fact that they play key roles in the regulation of immune responses to microbial pathogens, insect herbivores, and beneficial microbes (Pieterse et al., 2012). In brief the classical developmental growth regulators are considered as auxin, brassinosteroid, cytokinin, and gibberellin (GA), whilst abscisic acid, ethylene, jasmonic, and salicylic acid are often implicated in stress responses (Browse, 2009; Vlot et al., 2009; Wolters and Jurgens, 2009). However, the very recent identification of strigolactones as a further developmental growth regulators (Gomez-Roldan et al., 2008; Umehara et al., 2008; Alder et al., 2012) suggests that our current list of phytohormones may not yet be complete.