Overexpression of OsARD1 Improves Submergence, Drought, and Salt Tolerances of Seedling Through the Enhancement of Ethylene Synthesis in Rice.

Shanshan Liang,Wei-Jiang Luan,Ya-Jun Jin,Guoyou Ye,Xiaodong Xie,Wei Xiong,Cuicui Yin,Bo Yang,Siju Zhang,Shouyi Chen

doi:10.3389/fpls.2019.01088

Abstract

Acireductone dioxygenase (ARD) is a metal-binding metalloenzyme and involved in the methionine salvage pathway. In rice, OsARD1 binds Fe2+ and catalyzes the formation of 2-keto-4-methylthiobutyrate (KMTB) to produce methionine, which is an initial substrate in ethylene synthesis pathway. Here, we report that overexpression of OsARD1 elevates the endogenous ethylene release rate, enhances the tolerance to submergence stress, and reduces the sensitivity to drought, salt, and osmotic stresses in rice. OsARD1 is strongly induced by submergence, drought, salinity, PEG6000, and mechanical damage stresses and exhibits high expression level in senescent leaves. Transgenic plants overexpressing OsARD1 (OsARD1-OE) display fast elongation growth to escape submergence stress. The ethylene content is significantly maximized in OsARD1-OE plants compared with the wide type. OsARD1-OE plants display increased shoot elongation and inhibition of root elongation under the submergence stress and grow in dark due to increase of ethylene. The elongation of coleoptile under anaerobic germination is also significantly promoted in OsARD1-OE lines due to the increase of ethylene content. The sensitivity to drought and salt stresses is reduced in OsARD1-OE transgenic lines. Water holding capacity is enhanced, and the stomata and trichomes on leaves increase in OsARD1-OE lines. Drought and salt tolerance and ethylene synthesis–related genes are upregulated in OsARD1-OE plants. Subcellular localization shows that OsARD1 displays strong localization signal in cell nucleus, suggesting OsARD1 may interact with the transcription factors. Taken together, the results provide the understanding of the function of OsARD1 in ethylene synthesis and abiotic stress response in rice.

Highlights

Acireductone dioxygenase (ARD) is a metal-binding protein family belonging to the cupin superfamily (Dunwell et al, 2004)
Previous study showed that OsARD1 encodes an active ARD that can catalyze the formation of 2-keto-4-methylthiobutyrate to synthesize ethylene in Yang cycle (Yang and Hoffman, 1984; Wang et al, 2002)
We provide insights that OsARD1 is involved in ethylene synthesis and signaling pathway

Summary

Introduction

Acireductone dioxygenase (ARD) is a metal-binding protein family belonging to the cupin superfamily (Dunwell et al, 2004). ARD catalyzes the penultimate step in the methionine salvage pathway, the oxidative decomposition of substrate acireductone (1,2-dihydoxy-3-keto-5-[thiomethyl]-pent-1-ene) to formate and 2-keto-4-(thiomethyl) butyrate (KMTB), the keto-acid precursor of methionine. ARD bound with Fe2+ catalyzes on-pathway chemistry leading to production of formate and the keto-acid precursor to methionine, whereas ARD bound with Ni2+ catalyzes an off-pathway shunt leading to production of formate, carbon monoxide, and methylthiopropionate (MTP) (Wray and Abeles, 1995; Dai et al, 1999). In mouse (Mus musculus), ARD bound with Fe2+ catalyzes on-pathway chemistry resulting in formate and the ketoacid precursor of methionine, whereas the Ni2+, Co2+, or Mn2+ forms catalyze off-pathway chemistry, similar as ARD from Klebsiella (Deshpande et al, 2016). OsARD1 is strongly induced by ethylene and catalyzes the formation of KMTB to further produce methionine in the methionine salvage pathway (Sauter et al, 2005)

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Results

Conclusion