Genetic and Hormonal Blueprint of Shoot-Borne Adventitious Root Development in Rice and Maize.

The evolution of the root architecture in plants was a prerequisite for the absorption of water and minerals from the soil, thus becoming a major determinant of terrestrial plant colonization. Cereals have a remarkably complex root system consisting of embryonic primary roots and post-embryonic lateral roots and shoot-borne adventitious roots. Among grass species, rice adventitious roots (also called crown roots) are developed from compressed nodes at the stem base, whereas in maize, besides crown roots, several aboveground brace roots are also formed, thus displaying species-specific diversity in the adventitious root types. Despite being the backbone for the adult root system in monocots, adventitious roots are the least studied of all the plant organs. In recent times, molecular genetics, genomics, and proteomics-based approaches have been utilized to dissect the mechanism of post-embryonic meristem formation and tissue patterning. Adventitious root development is a cumulative effect of action and interaction of crucial genetic and hormonal regulators. In this review, we provide a comprehensive state-of-the-art on the key regulators involved during different stages of AR development in two important crop plants, rice, and maize. We have reviewed the role of major phytohormones, microRNAs, transcription factors, and their crosstalk during adventitious root development in these cereal crops.