Modulation of Arabidopsis root growth by specialized tritperenes
Unlike most animals, plants have limited abilities to move to encounter more favorable growing conditions. Accordingly, they have evolved connective and sophisticated programs, many of which are steered by multiple phytohormones, to tune their development to their surroundings. Phytohormones often act in a combinatorial way to regulate development, growth and defense programs in a cell- or organ-specific manner (Pieterse et al., 2012). Auxin, for instance, is the major hormone controlling root development (Motte et al., 2019). Likewise, jasmonate (JA) and its derivatives, collectively called the jasmonates (JAs), regulate a wide variety of defense responses, including the biosynthesis of specialized metabolites. Additionally, JAs control specific developmental and growth processes (De Geyter et al., 2012; Wasternack & Hause, 2013; Wasternack & Strnad, 2019). For instance, Arabidopsis thaliana seedlings treated with exogenous JA show shorter primary roots and more lateral roots (Sun et al., 2009; Hentrich et al., 2013). These phenotypic effects also were reported in auxin-treated plants and in mutants overproducing auxin (Cai et al., 2014). More recently, wound-induced JA was shown to promote stem cell activation and regeneration (Zhou et al., 2019). Besides sharing some signaling pathway components with auxin (Cuéllar Pérez & Goossens, 2013), JAs also have been reported to be involved in the regulation of auxin transport (Sun et al., 2011; Staswick et al., 2017) and biosynthesis (Sun et al., 2009; Hentrich et al., 2013). As such, JA and auxin are very intertwined to regulate root growth. Besides the JA-induced transcriptional activation of the PLETHORA transcription factors (Chen et al., 2011) that, in turn, regulate auxin transport and biosynthesis (Santuari et al., 2016), much remains to be uncovered about the molecular mechanisms of JA and auxin cross-talk.