As discussed above, it has often been suggested that members of the HD-Zip I and II families function as developmental regulators, specifically being involved in regulation of developmental adaptation to environmental stress conditions (e.g. Meijer et al. 1997; Lee and Chun 1998; Scarpella et al. 2000, 2002; Manavella et al. 2006; Komatsuda et al. 2007).