Osmotic stress represses strigolactone biosynthesis in Lotus japonicus roots: exploring the interaction between strigolactones and ABA under abiotic stress
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Strigolactone changes and cross talk with ABA unveil a picture of root-specific hormonal dynamics under stress.
Strigolactones (SLs) are carotenoid-derived hormones influencing diverse aspects of development and communication with (micro)organisms, and proposed as mediators of environmental stimuli in resource allocation processes; to contribute to adaptive adjustments, therefore, their pathway must be responsive to environmental cues. To investigate the relationship between SLs and abiotic stress in Lotus japonicus, we compared wild-type and SL-depleted plants, and studied SL metabolism in roots stressed osmotically and/or phosphate starved. SL-depleted plants showed increased stomatal conductance, both under normal and stress conditions, and impaired resistance to drought associated with slower stomatal closure in response to abscisic acid (ABA). This confirms that SLs contribute to drought resistance in species other than Arabidopsis. However, we also observed that osmotic stress rapidly and strongly decreased SL concentration in tissues and exudates of wild-type Lotus roots, by acting on the transcription of biosynthetic and transporter-encoding genes and independently of phosphate abundance. Pre-treatment with exogenous SLs inhibited the osmotic stress-induced ABA increase in wild-type roots and down-regulated the transcription of the ABA biosynthetic gene LjNCED2. We propose that a transcriptionally regulated, early SL decrease under osmotic stress is needed (but not sufficient) to allow the physiological increase of ABA in roots. This work shows that SL metabolism and effects on ABA are seemingly opposite in roots and shoots under stress.
KeywordsCarotenoid cleavage enzymes CCD7 CCD8 D27 MAX1 PDR1 NCED Drought GR24 (synthetic strigolactone analogue) Phosphate starvation Stomatal conductance
Arbuscular mycorrhizal fungi
Carotenoid cleavage dioxygenase
Decreased apical dominance
Expressed sequence tag
CCD7-knocked-down L. japonicus
More axillary growth
Pleiotropic drug resistance
We would like to thank Jens Stougaard (Aarhus University, Denmark) for the generous supply of Gifu B-129 seeds, Binne Zwanenburg (Radboud University, Nijmegen, The Netherlands) who kindly supplied some of the GR24 used and Tadao Asami (Department of Applied Biological Chemistry, University of Tokyo, Tokyo, Japan) for providing synthetic 5-deoxystrigol and D6-5-deoxystrigol. The authors also wish to thank Paola Bonfante (University of Turin, Italy) for continuous support on the topic. The research was funded by the BioBITs Project (Piedmont Region, Converging Technologies call 2007) and the SLEPS Project (Compagnia di S. Paolo and University of Turin, call 2012) to FC, AS, CL and IV, and by the Netherlands Organization for Scientific Research (NWO; Vici grant, 865.06.002, and Equipment grant, 834.08.001) to HJB. JL was funded by the Chinese Scholarship Council (CSC, Grant No. 2008108168).
Conflict of interest
FC, IV and AS hold a share of StrigoLab S.r.l., which provided part of the GR24 used in the study.
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