From tomato to Arabidopsis and back: role of strigolactones in the stomatal memory of drought stress

Plants are frequently exposed to repeated cycles of similar stresses; responding differently to them, thus displaying “stress memory”, is an adaptive strategy to cope with fluctuating environmental conditions. The so-called “after-effect” of drought, for example, is a feature of stress memory seen at the stomatal level: an incomplete recovery of conductance after drought, even when water potential has fully recovered. Besides the likely dependence on abscisic acid (ABA), the molecular and physiological mechanisms driving the after-effect are not clear yet. So, we set to investigate whether the phytohormones strigolactones may contribute to it. Interestingly in fact, among other roles, strigolactones promote stomatal closure in both ABA-dependent and independent manners, and are needed for effective drought acclimation processes. We investigated their physiological and molecular contributions to the after-effect, by contrasting stomatal conductance and transcriptome of wt versus strigolactone biosynthetic/signalling mutants of Arabidopsis and tomato in repeated dehydration cycles. In both model plants, strigolactones were needed for a sustained after-effect during recovery from the first stress. They were also indispensable in tomato for a full after-effect during recovery in the second cycle, in which stress avoidance by stomatal closure was overall stronger. Differently, Arabidopsis seems to adopt a different drought tolerance strategy (e.g. osmotic adjustment) by avoiding the stomatal closure during the second stress and recovery cycle. Since in both models however, strigolactones had been proven necessary for the after effect from the first stress, we took a RNA-seq and promoter analysis approach to investigate the links between strigolactones and transcriptome changes in both species under recovery conditions. Results will be presented that highlight how strigolactone-dependent specific transcription factor categories may underlie stomatal memory of drought.