МОЛЕКУЛЯРНО-ГЕНЕТИЧЕСКИЕ И ГОРМОНАЛЬНЫЕ МЕХАНИЗМЫ ВЕТВЛЕНИЯ КОРНЕВЫХ СИСТЕМ (обзор)

The most important function of any plant root system is the supply of mineral nutrients. The soil is a heterogeneous environment characterized by irregular distribution of nutrients. The branching of the main root which leads to the formation of the root system is regulated by the necessity of compensation for this unpredictable environment. Different types of root systems may reflect different strategies of adaptation of vascular plants to land (L. Kutschera et al., 1997). In recent years, a vast array of experimental data on this subject has been collected. Investigations were carried out on the model plant Arabidopsis thaliana (J.G. Dubrovsky et al., 2001; B. Parizot et al., 2012; J.G. Dubrovsky et al., 2017) as well as on a wide range of crops (cereals, crucifers, gourds, buckwheat etc.). The accumulated data allow the identification of economically important traits of root systems that can be exploited to design breeding strategies to optimize root system function. This review contains an analysis of the current data on cellular, molecular genetic and physiological mechanisms of lateral root initiation and development. The phytohormone auxin performs multiple functions during lateral root initiation (Y. Du et al., 2017). It participates in the earliest stages by determining of competence for the first division by pericycle cells that leads to primordium formation. Furthermore, auxin facilitates the emergence of the primordium from the parental root cortex. Recent studies have shown that the formation of the lateral root begins with the oscillation of auxin concentrations in the basal part of the parental root meristem and the formation of an auxin response maximum in some cells of central cylinder (I. De Smet et al., 2007; K.H. ten Tusscher et al., 2017). The next stage is the specification of founder cells in the pericycle and the subsequent formation of the prebranch site (M.A. Moreno-Risueno et al., 2010). Questions ranging from the mechanisms that determine which pericycle cells can become founder cells for lateral root primordia, the mechanisms of regulation of cell proliferation, the positioning of lateral roots along the axis of the parental root, and hormonal factors and their targets, all leading to the successive development of lateral roots, are discussed in this review. Data on the role of auxin in this process and on the mechanisms of auxin signal transduction in the course of lateral root initiation are provided. The key factors involved in the determination of the competence of pericycle cells to initiate lateral root primordia are the transcription factor GATA23 (B. De Rybel et al., 2010) and the membrane-associated kinase regulator MAKR4 (W. Xuan et al., 2015). Special attention is paid to the role of neighboring cell layers in the control of the initial stages of cell proliferation in the pericycle that result in the formation of a new organ. However, there are a number of families among flowering plants in which the initiation and development of lateral root primordia occurs directly in the parental root meristem (J.G. Dubrovsky, 1986, 1987; K.N. Demchenko et al., 2001; E.L. Ilina et al., 2012). For the first time, data on the key role of auxin in lateral root primordia initiation in these species, in particular in Cucurbitaceae, are presented in this review, and the mechanisms that open the opportunity for early and rapid branching of the main root are discussed. Special attention is paid to evolutionary mechanisms of branching site determination in flowering plants.