Strigolactones affect the stomatal and transcriptomic memory of repeated drought stress in tomato

Stress memory is an adaptive strategy for plants to cope with fluctuating environmental conditions. For example, it has been shown that the transcriptional responses to drought can be “trained”, i.e. changed, by a previous stress episode. Also, the so-called after-effect of drought 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. This effect has been shown to depend on the phytohormones abscisic acid and strigolactones, but whether and how repeated drought spells affect its intensity is unclear, as it is unclear how much of the “trainability” of physiological and molecular responses depends on strigolactones. This study investigated the contribution of strigolactones to physiological and transcriptional drought memory, by comparing the stomatal conductance and transcriptome of wild-type versus strigolactone-depleted tomato plants in repeated dehydration cycles. We found that the after-effect of drought can be primed by a previous drought episode; and, that strigolactones are indispensable for full priming. About half of the genes that display a drought memory profile require an intact strigolactone pathway for trainability. Several potential candidates are proposed as effectors of strigolactone-dependent drought memory, namely for enhanced ABA sensitivity and antioxidant activities, and for the maintenance of cellular homeostasis via enhanced protein preservation under environmental duress. Our findings bear applicative implications for stress resilience improvement in crops and help to explain why plants treated with synthetic strigolactones display improved performances under a very diverse array of stresses.