Strigolactones: A Novel Carotenoid-Derived Phytohormone – Biosynthesis, Transporters, Signalling, and Mechanisms in Abiotic Stress

Phytohormones (PHs) play central roles in improving the survival ability of plants to various abiotic stresses. The major PHs are auxins, abscisic acid (ABA), gibberellins (GAs), jasmonic acid (JA), salicylic acid (SA), ethylene (ET), cytokinin (CK), and brassinosteroids (BRs), and nitric oxide (NO), polyamines (PA), and plant peptide are also considered as PHs. Besides them, newly identified PHs are strigolactones (SLs) and karrikins (KARs). Among them, SLs have been categorized as novel carotenoid-derived PHs, although they were primarily recognized as host-derived stimulating substances for germination of parasitic weeds under the genera Striga and Orobanche. Lately, SLs were established as host detection and hyphal-branching signals for arbuscular mycorrhizal (AM) fungi. In plants, they control numerous developing processes which lead plants to acclimatize to survive various abiotic stresses, particularly heat, drought, cold, salinity and waterlogging. In the last decade, the detection of SLs provides a novel prospect to reconnoitre PHs regulation of plant for advance and adaptation to ecological restrictions. Recent investigations also recognized novel examples of PHs cross talk contributing in the adaptation of inclusive rejoinders in plants. In this chapter, we have discussed the biosynthesis, signalling, governing, and physiochemical roles of SLs in numerous abiotic stress conditions. Therefore, it is revealed that the comprehensive thoughtful of SLs will be a significant issue for overwhelming the difficulties of crop damage as a consequence of hostile environments.