International Journal of Molecular Sciences Review Understanding the Intricate Web of Phytohormone Signalling in Modulating Root System Architecture Manvi Sharma †, Dhriti Singh †, Harshita B. Saksena †, Mohan Sharma † , Archna Tiwari ‡, Prakhar Awasthi ‡, Halidev Krishna Botta ‡, Brihaspati Narayan Shukla § and Ashverya Laxmi * National Institute of Plant Genome Research, Aruna Asaf Ali Marg, New Delhi 110067, India;
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[email protected] (B.N.S.) * Correspondence:
[email protected]; Tel.: +91-11-26741612 (ext. 180) † Equal first authors. ‡ Equal second authors. § Third author. Abstract: Root system architecture (RSA) is an important developmental and agronomic trait that is regulated by various physical factors such as nutrients, water, microbes, gravity, and soil compaction as well as hormone-mediated pathways. Phytohormones act as internal mediators between soil and RSA to influence various events of root development, starting from organogenesis to the formation of higher order lateral roots (LRs) through diverse mechanisms. Apart from interaction with the external cues, root development also relies on the complex web of interaction among phytohormones to exhibit synergistic or antagonistic effects to improve crop performance. However, there are considerable Citation: Sharma, M.; Singh, D.; gaps in understanding the interaction of these hormonal networks during various aspects of root Saksena, H.B.; Sharma, M.; Tiwari, A.; development. In this review, we elucidate the role of different hormones to modulate a common Awasthi, P.; Botta, H.K.; Shukla, B.N.; phenotypic output, such as RSA in Arabidopsis and crop plants, and discuss future perspectives to Laxmi, A.