Editorial: [Advances on the biological mechanisms involved in adventitious root formation: from signaling to morphogenesis]

Abstract

The neoformation of adventitious roots in cuttings is the key in the success of plant vegetative propagation systems. Two main steps are recognized in adventitious root (AR) formation. The first is known as the induction phase, in which high auxin levels are required for reprogramming of competent cells toward root development, which is further linked to other biochemical changes (Ahkami et al., 2013; Druege et al., 2019). This stage is followed by the formation phase, when cell division, differentiation and growth occur, leading to AR primordium development and, finally, to AR emergence/expression (Da Costa et al., Druege et al., 2019). Based on fossil records and phylogenetic data, Mhimdi and Pérez-Pérez proposed AR formation as the default state of root development in plants, highlighting that root initiation from non-root tissues might be considered as an ancestral trait, as ARs are formed by default in lycophytes and ferns. According to the same authors, in many angiosperms, AR formation seems to be repressed through mechanisms that maintain competent cells in a quiescent state. Activation of competent cells is triggered by environmental conditions to which the cuttings or intact plants are exposed, like exogenous auxin treatment, wounding, waterlogging, or light exposure and mineral nutrition determining the activation of a complex network of signaling, metabolic, and transport pathways (Bannoud and Bellini, Mhimdi and Pérez-Pérez, Yang et al., 2019). All these network pathways are under the control of distinct genes, being at the end responsible for efficient cell reprogramming, acquisition of a new evolutionary pattern and de novo organ differentiation and development.