Root halotropism in plants: tolerance or escape?

Abstract

Natural world is composed of fascinating diversity of life-forms and numerous adaptation strategies in the changing environment especially in the plant kingdom. An adaptive plant root response in saline environment to circumnavigate a stressful atmosphere by a directional growth away from salinity is known as halotropism, which is accomplished by the redistribution of phytohormone auxin at the root tip by PIN-FORMED 2 (PIN2) auxin efflux carrier. In this article, we review the role of salt-induced phospholipase D activity, endocytosis of auxin efflux carrier in cell membrane, asymmetry of auxin distribution, ABCB transporters, protein phosphatase 2A, auxin metabolism, phytohormones, microtubule and cell wall glycoprotein in the regulation of root halotropism. As climate change and increased soil salinity are two most important causal factors behind reduction in yield and crop diversity threatening global agriculture, we have summarized key advances in root halotropism and emphasized the importance of gaining a comprehensive understanding on the mechanism of root halotropism in crop plants, which might enable in designing plants with modulated root architecture to enhance crop adaptability and yield in saline soil for ensuring food security across the globe.