Strigolactone metabolism is shut down by osmotic stress in Lotus japonicus roots, likely to allow stress-induced ABA accumulation.

Strigolactones (SLs) are plant hormones proposed as mediators of environmental stimuli in resource allocation processes, for which purpose they must be responsive to environmental conditions. We quantified SLs in tissues and exudates of Lotus japonicus roots stressed osmotically and/or P starved. The transcripts of SL-related genes were quantified. Also, root ABA and physiological performances of SL-depleted plants were studied under drought, and the effect of excess SLs on ABA was recorded in stressed WT roots. Results showed that osmotic stress rapidly and strongly decreases SL abundance in root exudates and extracts, independently of P abundance. This was associated with less transcript of most SL-related genes. While SL-depleted Lotus plants showed only a subtle phenotype under drought, pre-treatment with exogenous SLs inhibited the osmotic stress-induced ABA increase in WT roots, down-regulating the transcription of the biosynthetic gene LjNCED2. In conclusion, we hypothesize that fast SL decrease under osmotic stress allows the physiological increase of ABA, and that SLs are likely to affect plant acclimation by modulating ABA metabolism and possibly, sensitivity.