Abstract
The L-ascorbate peroxidase 6 gene (APX6) is one of the most important genes for scavenging H2O2 and plays a vital role in plant resistance to environmental stresses. In this study, a novel ScAPX6 gene (GenBank Accession No. KT907352) was obtained from a sugarcane variety (ROC22). Bioinformatics analysis showed that ScAPX6 has a cDNA length of 1,086 bp and encoded 333 amino acid residues. Subcellular localization confirmed that ScAPX6 was located in the chloroplast. Enhanced growth of Escherichia coli BL21 cells that expressed ScAPX6 showed high tolerance under copper (Cu) stress. Real-time quantitative PCR analysis revealed that ScAPX6 was constitutively expressed wherein with the highest expression levels in sugarcane pith and leaf and the lowest in the root. ScAPX6 was down-regulated by salicylic acid (SA), hydrogen peroxide (H2O2), polyethylene glycol (PEG) and sodium chloride (NaCl) stimuli. Interestingly, it was significantly up-regulated under the stresses of abscisic acid (ABA) and methyl jasmonate (MeJA) wherein with the highest inducible expression levels at 6 h at 6.0- and 70.0-times higher, respectively than that of control. Overexpression of ScAPX6 in Nicotiana benthamiana leaves enhanced the resistance to the infection of tobacco pathogens Pseudomonas solanacearum and Fusarium solani var. coeruleum. These results implied that ScAPX6 might positively respond to ABA, MeJA, and Cu, but might negatively respond to the stresses of SA, H2O2, PEG, and NaCl. Keeping in view the current investigation, ScAPX6 could be associated with the hypersensitive response (HR) or immunity of sugarcane, which will provide a baseline for the function identification of sugarcane ScAPX6.
Highlights
In addition to Oryza sativa, Triticum aestivum, and Zea mays, sugarcane is the fourth largest staple food for the people of China
The results showed that sequence of a putative APX6 unigene (ScAPX6) and the chloroplast marker were located in the same place, so it was confirmed that ScAPX6 was located in the chloroplast, which is in accordance with the results of prediction (Figure 4)
ScAPX6 was constitutively expressed in sugarcane tissues and with the highest expression in pith but the lowest in root (Figure 7)
Summary
In addition to Oryza sativa, Triticum aestivum, and Zea mays, sugarcane is the fourth largest staple food for the people of China. Environmental stimuli can induce active oxygen system which may cause injury to plant cells (Mittler et al, 2004, 2011). Peroxidases (EC number 1.11.1.x), including glutathione peroxidase (GPX), catalase (CAT), and ascorbate peroxidase (APX), are widespread in organisms and can remove the reactive oxygen (Shigeoka et al, 2002; Apel and Hirt, 2014). APX, belonging to type I heme peroxidase and copper oxidase family, is widely employed in plants and can rapidly scavenge hydrogen peroxide (H2O2) in the ascorbic acid (ASA) and glutathione (GSH) cycle (Shigeoka et al, 2002). The role of APX is highly specific to ascorbic acid, that is, to help electron donor to oxidation (Chen and Asada, 1989; Mittler, 2002; Foyer and Noctor, 2005)
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