A tale of plant hormones: how strigolactones cross-talk with ABA to set drought responses in tomato

Strigolactones are carotenoid-derived metabolites with a multitude of functions, both in the plant and in the rhizosphere. They have a prominent role as hormones, influencing whole-plant morphology and development also in response to environmental stress. In tomato (Solanum lycopersicum L.) and other dicots experiencing drought, their synthesis partly shifts from roots to shoots. The drop in root-synthesised strigolactones seems to exert local effects on ABA levels and mobilisation within root tissues. However, it also acts as a systemic signal triggering strigolactone synthesis in the leaves and priming guard-cell sensitivity to ABA, thus governing a delayed recovery of stomatal conductance after stress (the so-called “after-effect”), and better stress avoidance during the next drought spell. The microRNA mir156, a highly conserved microRNA, was identified as a good candidate mediator of the ABA-dependent subset of drought responses controlled by strigolactones. This is based on the correlation with, and strict requirement for endogenous strigolactones in miR156 induction by drought; and on the ecophysiological and molecular effects of excess strigolactones vs miR156. Its systemic mobility pattern also defines miR156 as a strigolactone-related signal feeding back from the shoot to the root in response to stress, possibly to influence the increase in root water use efficiency under drought. A preliminary model will be presented, which captures organ-specific strigolactone action and dynamics under drought in tomato. Our work has received funding from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement n. 727929 - TOMRES