Abstract
Recovery of the root system following physical damage is an essential issue for plant survival. An injured root system is able to regenerate by increases in lateral root (LR) number and acceleration of root growth. The horticultural technique of root pruning (root cutting) is an application of this response and is a common garden technique for controlling plant growth. Although root pruning is widely used, the molecular mechanisms underlying the subsequent changes in the root system are poorly understood. In this study, root pruning was employed as a model system to study the molecular mechanisms of root system regeneration. Notably, LR defects in wild-type plants treated with inhibitors of polar auxin transport (PAT) or in the auxin signaling mutant auxin/indole-3-acetic acid19/massugu2 were recovered by root pruning. Induction of IAA19 following root pruning indicates an enhancement of auxin signaling by root pruning. Endogenous levels of IAA increased after root pruning, and YUCCA9 was identified as the primary gene responsible. PAT-related genes were induced after root pruning, and the YUCCA inhibitor yucasin suppressed root regeneration in PAT-related mutants. Therefore, we demonstrate the crucial role of YUCCA9, along with other redundant YUCCA family genes, in the enhancement of auxin biosynthesis following root pruning. This further enhances auxin transport and activates downstream auxin signaling genes, and thus increases LR number.
Highlights
Organ regeneration is a distinctive feature of plants that contributes to their robustness in adverse conditions
Red arrowheads indicate the point 12 mm from the root–shoot junction that corresponds to the cut point. (B) The number of lateral root (LR) was counted in the 12 mm area from the root–shoot junction. (C) Growth rate of the first emerged LR. (D) Total length of the root system of intact or root-cut plants 4 d after root cutting was calculated as the sum of the length of the primary root and every LR. (E) Progress of LR development after root cutting
The combination of yucasin and naphthylphthalamic acid (NPA) completely blocked LR formation in both intact and root-cut WT plants (Fig. 4F). These results indicate that auxin biosynthesis is the primary factor for RCN, while both auxin biosynthesis and polar auxin transport (PAT) activities together are necessary for the maximum RCN
Summary
Organ regeneration is a distinctive feature of plants that contributes to their robustness in adverse conditions. When part of the root system is removed by root pruning, the plants are able to regenerate a new root system with a smaller size and more branches (Wang et al 2014) This new root system provides an efficient intensive production system with reduced vegetative growth (by reducing the flow of nutrients, water and hormones from root to shoot), which led to the promotion of solar radiation interception, increased flower buds, more regular production (Rademacher 2004, Vercammen et al 2005, Rodrıguez-Gamir et al 2010, Carra et al 2017), as well as the production of better quality fruit with smaller size, firmer fruit, more soluble solids content and less pre-harvest drop (Schupp and Ferree 1987, Ferree 1992, Carra et al 2017). The regeneration of the root system following root pruning through the induction of lateral root (LR) formation has long been reported in different plant species
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