Transcriptome Analysis Points to BES1 as a Transducer of Strigolactone Effects on Drought Memory in Arabidopsis thaliana

Strigolactones (SLs) are carotenoid-derived phytohormones governing a wide range of physiological processes, including drought-associated stomatal closure. We have previously shown in tomato that SLs regulate the so-called after-effect of drought, whereby stomatal conductance is not completely restored for some time during recovery after a drought spell, irrespective of the water potential. To ease the elucidation of its molecular underpinnings, we investigated whether this SL effect is conserved in Arabidopsis thaliana by contrasting the physiological performances of the wild-type with SL-depleted (more axillary growth 4, max4) and insensitive (dwarf 14, d14) mutants in a drought and recovery protocol. Physiological analyses showed that SLs are important to achieve a complete after-effect in A. thaliana while transcriptome results suggested that the SL-dependent modulation of drought responses extends to a large subset (about 4/5) of genes displaying memory transcription patterns. Among these, we show that the activation of over thirty genes related to ABA metabolism and signalling strongly depends on SL signalling. Furthermore, by using promoter-enrichment tools, we identified putative cis- and trans-acting factors that may be important in the SL-dependent and independent regulation of genes during drought and recovery. Finally, in order to test the accuracy of our bioinformatic prediction, we confirmed one of the most promising transcription factor candidates mediating SL signalling effects on transcriptional drought memory: BRI-EMS SUPPRESSOR1 (BES1). Our findings reveal that SLs are master regulators of Arabidopsis transcriptional memory upon drought and that this role is partially mediated by the BES1 transcription factor.