Transgenic Centipedegrass (Eremochloa ophiuroides [Munro] Hack.) Overexpressing S-Adenosylmethionine Decarboxylase (SAMDC) Gene for Improved Cold Tolerance Through Involvement of H2O2 and NO Signaling.

Jianhao Luo,Zhenfei Guo,Jingjing Chen,Peipei Zhang,Mingxi Liu,Shaoyun Lu,Chendong Zhang

doi:10.3389/fpls.2017.01655

Abstract

Centipedegrass (Eremochloa ophiuroides [Munro] Hack.) is an important warm-season turfgrass species. Transgenic centipedgrass plants overexpressing S-adenosylmethionine decarboxylase from bermudagrass (CdSAMDC1) that was induced in response to cold were generated in this study. Higher levels of CdSAMDC1 transcript and sperimidine (Spd) and spermin (Spm) concentrations and enhanced freezing and chilling tolerance were observed in transgenic plants as compared with the wild type (WT). Transgenic plants had higher levels of polyamine oxidase (PAO) activity and H2O2 than WT, which were blocked by pretreatment with methylglyoxal bis (guanylhydrazone) or MGBG, inhibitor of SAMDC, indicating that the increased PAO and H2O2 were a result of expression of CdSAMDC1. In addition, transgenic plants had higher levels of nitrate reductase (NR) activity and nitric oxide (NO) concentration. The increased NR activity were blocked by pretreatment with MGBG and ascorbic acid (AsA), scavenger of H2O2, while the increased NO level was blocked by MGBG, AsA, and inhibitors of NR, indicating that the enhanced NR-derived NO was dependent upon H2O2, as a result of expression CdSAMDC1. Elevated superoxide dismutase (SOD) and catalase (CAT) activities were observed in transgenic plants than in WT, which were blocked by pretreatment with MGBG, AsA, inhibitors of NR and scavenger of NO, indicating that the increased activities of SOD and CAT depends on expression of CdSAMDC1, H2O2, and NR-derived NO. Our results suggest that the elevated cold tolerance was associated with PAO catalyzed production of H2O2, which in turn led to NR-derived NO production and induced antioxidant enzyme activities in transgenic plants.

Highlights

Polyamines are important plant regulators involving in plant growth, development and adaptation to environmental stresses (Minocha et al, 2014; Shi and Chan, 2014; Liu et al, 2015)
Leaf fragments of transgenic plants and wild type (WT) were placed in deionized water for 1 h to eliminate the potential wound stress, and placed in beakers containing 1 mM methylglyoxal bis or MGBG, 1 mM ascorbic acid (AsA), 1 mM NaN2, 100 mM tungstate, or 200 mM 2-phenyl-4,4,5,5tetramethylimidazoline-1-oxyl3-oxide (PTIO) under light of 80 mmol photons m−2 s−1 for 12 h, while those treated with deionized water for 12 h under the same condition served as a control
The results indicated that the elevated nitrate reductase (NR) and nitric oxide (NO) were associated with accumulation of H2O2 as a result of expression of CdSAMDC1, while the elevated NO was dependent upon NR

Summary

Introduction

Polyamines are important plant regulators involving in plant growth, development and adaptation to environmental stresses (Minocha et al, 2014; Shi and Chan, 2014; Liu et al, 2015). Spd is synthesized from decarboxylated S-adenosylmethionine (dcSAM) and Put, catalyzed by Spd synthase, while dcSAM is formed from S-adenosylmethionine (SAM), catalyzed by SAM decarboxylase (SAMDC). Spm is synthesized from Spd and Put, catalyzed by Spm synthase (SPMS, Supplementary Figure S1; Liu et al, 2015). Polyamines are oxidized to produce H2O2 catalyzed by polyamine oxidase (Liu et al, 2015). H2O2 and NO are signaling in multiple physiological processes including adaptation to environmental stresses (Desikan et al, 2004; Miller et al, 2008; Zhao et al, 2009; Farnese et al, 2016; Niu and Liao, 2016; Sewelam et al, 2016; Singh et al, 2016)

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