Organ-specific dynamics and roles of strigolactones under drought

The phytohormones strigolactones (SL) are mostly produced in roots to be exuded in soil and transported to the shoot, where they modulate development. SL biosynthesis in shoots is necessary also for acclimatisation to drought in several plant species, mostly because it promotes stomata closure in abscisic acid (ABA)-dependent and independent ways. In tomato (Solanum lycopersicum L.) and other dicots under drought, their synthesis partly shifts from roots to shoots, indicating organ specificity in their metabolism and role. Such drop in root-synthesised SL acts as a systemic indication of stress unlinked from shootward ABA translocation and sufficient to prime the plant for better stress avoidance. Downstream effectors linking SL action under stress to ABA-dependent or independent responses however, are less characterised. We found that endogenous SL are absolutely required for miR156 induction by drought and that exogenous SL are sufficient for miR156 accumulation in tomato leaves. The effects of SL are exerted on MIR156 genes at the transcriptional and pri-miRNA processing level. mir156 is a highly conserved microRNA with roles in development and stress responses; its effects on target mRNA stability, tomato ecophysiology and stomatal behaviour suggest it as a good candidate mediator of the ABA-dependent subset of drought responses triggered by SL. The systemic mobility of miR156 defines it also as a SL-related signal feeding back from the shoot to the root in response to drought. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement n. 727929 - TOMRES