A Role for Auxin in Ethylene-Dependent Inducible Aerenchyma Formation in Rice Roots.

Takaki Yamauchi,Akihiro Tanaka,Mikio Nakazono,Nobuhiro Tsutsumi,Yoshiaki Inukai

doi:10.3390/plants9050610

Abstract

Internal oxygen diffusion from shoot to root tips is enhanced by the formation of aerenchyma (gas space) in waterlogged soils. Lysigenous aerenchyma is created by programmed cell death and subsequent lysis of the root cortical cells. Rice (Oryza sativa) forms aerenchyma constitutively under aerobic conditions and increases its formation under oxygen-deficient conditions. Recently, we have demonstrated that constitutive aerenchyma formation is regulated by auxin signaling mediated by Auxin/indole-3-acetic acid protein (AUX/IAA; IAA). While ethylene is involved in inducible aerenchyma formation, the relationship of auxin and ethylene during aerenchyma formation remains unclear. Here, we examined the effects of oxygen deficiency and ethylene on aerenchyma formation in the roots of a rice mutant (iaa13) in which auxin signaling is suppressed by a mutation in the degradation domain of IAA13 protein. The results showed that AUX/IAA-mediated auxin signaling contributes to ethylene-dependent inducible aerenchyma formation in rice roots. An auxin transport inhibitor abolished aerenchyma formation under oxygen-deficient conditions and reduced the expression of genes encoding ethylene biosynthesis enzymes, further supporting the idea that auxin is involved in ethylene-dependent inducible aerenchyma formation. Based on these studies, we propose a mechanism that underlies the relationship between auxin and ethylene during inducible aerenchyma formation in rice roots.

Highlights

Internal oxygen movement from shoot to roots through aerenchyma is essential for plants to adapt to waterlogged soils [1]
The differences were comparable at 30 mm and became smaller in the wild type (WT) than those in iaa13 at 40 to 50 mm (Figure 3a,b). These results suggest that ethylene-dependent aerenchyma formation in iaa13 is reduced at the apical part of the roots
The present results demonstrate that auxin is required for inducible aerenchyma formation in rice present results demonstrate that auxin required for inducible aerenchyma formation in roots.The

Summary

Introduction

Internal oxygen movement from shoot to roots through aerenchyma is essential for plants to adapt to waterlogged soils [1]. Mays) and wheat (Triticum aestivum), lysigenous aerenchyma is not generally formed under aerobic conditions, but its formation is induced under oxygen-deficient conditions [4,5,6,7]. In roots of the wetland plant rice (Oryza sativa), lysigenous aerenchyma is formed constitutively even under aerobic conditions (constitutive aerenchyma formation), and its formation is further increased under oxygen-deficient conditions (inducible aerenchyma formation) [4]. Ethylene is involved in inducible aerenchyma formation in rice roots [4,5,6,7]. Ethylene-induced production of reactive oxygen species (ROS) by respiratory burst oxidase homolog H (RBOHH) is involved in inducible aerenchyma formation in rice roots [12]. Ethylene and ROS signaling is involved in lysigenous aerenchyma formation in rice shoots [13]

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