The Coordination of Ethylene and Other Hormones in Primary Root Development

Abstract

The primary root is the basic component of root systems, initiates during embryogenesis and develops shortly after germination, and plays a key role in early seedling growth and survival. The phytohormone ethylene shows significant inhibition of the growth of primary roots. Recent findings have revealed that the inhibition of ethylene in primary root elongation is mediated via interactions with phytohormones, such as auxin, abscisic acid, gibberellin, cytokinins, jasmonic acid, and brassinosteroids. Considering that Arabidopsis and rice are the model plants of dicots and monocots, as well as the fact that hormonal crosstalk in primary root growth has been extensively investigated in Arabidopsis and rice, a better understanding of the mechanisms in Arabidopsis and rice will increase potential applications in other species. Therefore, we focus our interest on the emerging studies in the research of ethylene and hormone crosstalk in primary root development in Arabidopsis and rice.

Keywords: crosstalk; elongation; ethylene; hormones; primary root.

Figure 1

Crosstalk of ethylene and other hormones in the primary root growth of Arabidopsis and rice. In Arabidopsis, ethylene inhibits primary root growth by regulating auxin biosynthesis, transport, and signaling. EIN3/EIL1, ERF1, and HB52 function as crosstalk nodes between ethylene and auxin in this process. ABA promotes ethylene biosynthesis by affecting the posttranscriptional regulation of ACS. GA and ethylene antagonistically regulate the stability of DELLA proteins, which act as growth repressors. CKs induce ethylene biosynthesis by stabilizing ACS stability. Low concentrations of BRs inhibit ethylene biosynthesis by activating BZR1 and BES1 to repress the expression of ACSs. High levels of BRs induce ethylene biosynthesis through increasing the stability of ACSs. In rice, ethylene restricts primary root growth by increasing auxin and ABA biosynthesis. Auxin accumulation promotes SOR1-mediated degradation of OsIAA26, thus repressing normal root growth. MHZ3 stabilizes OsEIN2 to facilitate ethylene signal transduction. The solid lines indicate direct interactions, and the dashed lines indicate indirect interactions. The arrows indicate stimulatory effects, whereas the T sharp symbol indicates inhibitory effects.