Abstract
Plants modulate root growth in response to changes in the local environment, guided by intrinsic developmental genetic programs. The hormone Abscisic Acid (ABA) mediates responses to different environmental factors, such as the presence of nitrate in the soil, water stress and salt, shaping the structure of the root system by regulating the production of lateral roots as well as controlling root elongation by modulating cell division and elongation. Curiously, ABA controls different aspects of root architecture in different plant species, perhaps providing some insight into the great diversity of root architecture in different plants, both from different taxa and from different environments. ABA is an ancient signaling pathway, acquired well before the diversification of land plants. Nonetheless, how this ancient signaling module is implemented or interacts within a larger signaling network appears to vary in different species. This review will examine the role of ABA in the control of root architecture, focusing on the regulation of lateral root formation in three plant species, Arabidopsis thaliana, Medicago truncatula and Oryza sativa. We will consider how the implementation of the ABA signaling module might be a target of natural selection, to help contribute to the diversity of root architecture in nature.
Highlights
Plants display an extraordinary diversity of form that distinguishes members of different taxa, and individuals of the same species, even those that are genetically identical
It is tempting to speculate that MtNPF6.8 might function as a nitrate sensor, just as AtNPF6.3 does in Arabidopsis roots, and coordinate nitrate sensing with root growth, both through control of elongation and of Lateral roots (LRs) formation, via Abscisic Acid (ABA) transport
LBD transcription factors are associated both with LR initiation in Arabidopsis and with the root tip oscillations of gene expression that lead to prebranch point initiation [45,118], suggesting that ABA may intersect with this conserved signaling module to regulate developmental plasticity in response to environmental stress
Summary
Plants display an extraordinary diversity of form that distinguishes members of different taxa, and individuals of the same species, even those that are genetically identical. This variation in form reveals differences in growth history. The pattern of root branching and elongation, and the overall shape of the root system, is determined by a series of interactions of the root with its environment over the course of the plant’s lifetime. Coordination of growth and development in different tissues and different regions of the root system in response to this environmental stimulus is usually mediated by hormones. There is a growing awareness of the role of ABA in environmentally-regulated plant developmental processes, especially in the modulation of root architecture
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