Strigolactones promote flowering through the miR319-LANCEOLATE-SINGLE FLOWER TRUSS module in tomato

Strigolactones are a class of phytohormones with various functions in plant development, stress responses, and in the interaction with (micro)organisms in the rhizosphere. As developmental regulators, they control above and below-ground morphology, but while their effects on vegetative development are rather well studied, little is known about their role in reproduction. We investigated the mechanisms underlying reported defects by strigolactone-related mutants in solanaceous plants, using tomato as a model. The results showed that strigolactone levels in the shoot, whether endogenous or exogenous, inversely correlate with the time from germination to flowering, with the number of flowers and with the transcript levels of the florigen-encoding gene SINGLE FLOWER TRUSS (SFT) in the leaves. Genome-wide and targeted transcript quantifications coupled to metabolite analyses demonstrated for the first time that strigolactones induce the activation of the miR319-LA (LANCEOLATE) module in tomato leaves, and affect the gibberellin flowering pathway in tomato. The induction of SFT by exogenous strigolactones can occur both before and after floral transition, and is blocked in plants expressing a miR319-resistant version of LA under the control of the LA native promoter. Our study represents the first positioning of strigolactones in the context of the flowering regulation network in any plant species.