Abstract
Strigolactones (SLs) or their derivatives have recently been defined as novel phytohormones that regulate root development. However, it remains unclear whether SLs mediate root growth in response to phosphorus (P) and nitrogen (N) deficiency. In this study, the responses of root development in rice (Oryza sativa L.) to different levels of phosphate and nitrate supply were investigated using wild type (WT) and mutants defective in SL synthesis (d10 and d27) or insensitive to SL (d3). Reduced concentration of either phosphate or nitrate led to increased seminal root length and decreased lateral root density in WT. Limitation of either P or N stimulated SL production and enhanced expression of D10, D17, and D27 and suppressed expression of D3 and D14 in WT roots. Mutation of D10, D27, or D3 caused loss of sensitivity of root response to P and N deficiency. Application of the SL analogue GR24 restored seminal root length and lateral root density in WT and d10 and d27 mutants but not in the d3 mutant, suggesting that SLs were induced by nutrient-limiting conditions and led to changes in rice root growth via D3. Moreover, P or N deficiency or GR24 application reduced the transport of radiolabelled indole-3-acetic acid and the activity of DR5::GUS auxin reporter in WT and d10 and d27 mutants. These findings highlight the role of SLs in regulating rice root development under phosphate and nitrate limitation. The mechanisms underlying this regulatory role involve D3 and modulation of auxin transport from shoots to roots.
Highlights
The ability of plants to sense the availability of soil nutrients and to respond is of fundamental importance for their adaptation to the environment
The average length of lateral root (LR) in wild type (WT) plants increased by approximately 64% with 1 or 2 μM phosphate, while LR density in WT decreased by 40% with low-P treatment relative to SP treatment
A 22% increase in LR length and 20% decrease in LR density were observed in WT plants grown with 0.01 or 0.02 mM nitrate compared with SN treatment
Summary
The ability of plants to sense the availability of soil nutrients and to respond is of fundamental importance for their adaptation to the environment. The plasticity of root development in response to nitrogen (N) or phosphorus (P) deficiency is vital, as N and P are two major nutrients required for plant growth and development (Forde and Lorenzo, 2001; López-Bucio et al, 2003). Increased root-to-shoot ratio and root surface area induced by deficiency of N and P has been reported for several plant species (López-Bucio et al, 2003; Chun et al, 2005; Gruber et al, 2013). Various plant growth studies have concentrated on the responses of root systems of different species under conditions of phosphate deficiency. A significant phosphate deficiency-induced response in Arabidopsis thaliana involves reduction of primary root growth and enhancement of lateral root (LR) density (Williamson et al, 2001; Linkohr et al, 2002; Chevalier et al, 2003; López-Bucio et al, 2003; PérezTorres et al, 2008). In contrast to Arabidopsis, elongation of 6736 | Sun et al
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