The Interaction between Auxin and Nitric Oxide Regulates Root Growth in Response to Iron Deficiency in Rice

Huwei Sun,Fan Feng,Juan Liu,Quanzhi Zhao

doi:10.3389/fpls.2017.02169

Abstract

Fe deficiency (-Fe) is a common abiotic stress that affects the root development of plants. Auxin and nitric oxide (NO) are key regulator of root growth under -Fe. However, the interactions between auxin and NO regulate root growth in response to Fe deficiency are complex and unclear. In this study, the indole-3-acetic acid (IAA) and NO levels in roots, and the responses of root growth in rice to different levels of Fe supply were investigated using wild type (WT), ospin1b and osnia2 mutants. -Fe promoted LR formation but inhibited seminal root elongation. IAA levels, [3H] IAA transport, and expression levels of PIN1a-c genes in roots were reduced under -Fe, suggesting that polar auxin transport from shoots to roots was decreased. Application of IAA to -Fe seedlings restored seminal root length, but not LR density, to levels similar to those under normal Fe (+Fe), and the seminal root length was shorter in two ospin1b mutants relative to WT under +Fe, but not under -Fe, confirming that auxin transport participates in -Fe-inhibited seminal root elongation. Moreover, -Fe-induced LR density and -Fe-inhibited seminal root elongation paralleled NO production in roots. Interestingly, similar NO accumulation and responses of LR density and root elongation were observed in osnia2 mutants compared to WT, and the higher expression of NOA gene under -Fe, suggesting that -Fe-induced NO was generated via the NO synthase-like pathway rather than the nitrate reductase pathway. However, IAA could restore the functions of NO in inhibiting seminal root elongation, but did not replace the role of NO-induced LR formation under -Fe. Overall, our findings suggested that NO functions downstream of auxin in regulating LR formation; NO-inhibited seminal root elongation by decreasing meristem activity in root tips under -Fe, with the involvement of auxin.

Highlights

Iron (Fe) is a major nutrient needed for plant growth and development, and Fe deficiency dramatically affects plant growth, formation, and productivity (Guerinot and Yi, 1994)
We examined lateral root (LR) density, LR primordia number, and seminal root length after application of naphthylphthalamic acid (NPA) and indole-3-acetic acid (IAA) to determine whether the decreased auxin level resulting from −Fe was responsible for morphological changes of underground roots
The LR density and seminal root length of rice plants supplied with 0–1000 nM NPA under +Fe and 0–1000 nM IAA under −Fe were measured (Supplementary Figure 2)

Summary

Introduction

Iron (Fe) is a major nutrient needed for plant growth and development, and Fe deficiency dramatically affects plant growth, formation, and productivity (Guerinot and Yi, 1994). Despite the high level of Fe in soil, the solubility and availability of Fe are low in calcareous soil, which accounts for 30% of cultivated land worldwide Fe deficiency reduces both the growth and productivity of plants (Guerinot and Salt, 2001); an understanding. To adapt to Fe-deficient (−Fe) conditions, plants have developed multiple strategies to absorb Fe, such as the improvement of Fe uptake by regulating the expression of Fe-related genes (Yang et al, 2013) or a change in root morphology (Wang et al, 2010; Jin et al, 2011; Chen and Kao, 2012; Meng et al, 2012; Zhai et al, 2016). The responses of roots to Fe stress at the physiological level are well documented, the mechanisms underlying these changes are unclear

Methods

Results

Discussion

Conclusion