On the strigolactones - salicylic acid relationship in tomato under drought

Strigolactones (SL) are phytohormones with both an exogenous role as ecological communicators when exuded in soil, and endogenous as developmental regulators in the producing plant. They were more recently involved in responses to abiotic stress such as nutrient and water deprivation. Namely in tomato (Solanum lycopersicum L.), the current model places a drought-triggered decrease in root-produced SL upstream of a reduced shootward flow of SL and of increased SL synthesis in above-ground organs. Perception of shoot-produced SL leads in turn to higher sensitivity to ABA at the guard cell level and to lower transpiration, thus increasing drought tolerance. However, while the SL-ABA cross-talk is starting to be unravelled, not much is known about the interaction between SL and other hormones under drought. Salicylic acid (SA) is induced by drought, although its role and regulation in the process are not well elucidated. We analysed free SA content in roots and shoots of WT and SL-depleted tomato plants both under normal and water deprivation conditions. Results suggest that 1) SA is increased by drought both in roots and shoots as expected; 2) free SA concentration in WT root tissues under drought is decreased if shoots are not WT but SL-depleted, as demonstrated by reciprocal grafting experiments; 3) the same SL-dependent regulation is not obvious in shoots. The possibility that SL regulate the transcription of SA biosynthetic and catabolic genes is currently being investigated.