5.2. Strigolactones as central modulators of growth forms?
Taken together, both shoot branching and secondary growth are plastic processes that are highly influenced by the environment. SL signaling represses axillary bud outgrowth and induces cambium activity. Based on these observations, we have previously hypothesized that SLs are growth regulators used by plants to adjust their aerial architecture by modulating shoot branching and secondary growth in opposite directions (Agusti et al., 2011a). Depending on environmental input, plants would exhibit either a bushier form displaying a strong outgrowth of side shoots and a weak main stem, or a form in which the main shoot dominates and displays enhanced secondary growth (Fig. 1). The capacity to change between these growth forms may represent a significant advantage when growing in changing environmental conditions. Overall, the regulation of branching and secondary growth,
and the role of SLs as pivotal modulators, constitutes a potential example of developmental plasticity important for environment-dependent growth and achieving a fitness optimum. To what degree are both processes coordinated, and what role does SL signaling play in this coordination? If there is coordination, to what extent is it fixed genetically? Does it vary among populations? Is this a case of developmental flexibility driving genetic adaptation to specific environments?