Abstract

Beta-1,3-glucanases (EC 3.2.1.39), commonly known as pathogenesis-related (PR) proteins, play an important role not only in plant defense against fungal pathogens but also in plant physiological and developmental processes. However, only a limited number of sugarcane beta-1,3-glucanase genes have been isolated. In the present study, we identified and characterized a new beta-1,3-glucanase gene ScGluD2 (GenBank Acc No. KF664181) from sugarcane. An X8 domain was present at the C terminal region of ScGluD2, suggesting beta-1,3-glucan-binding function. Phylogenetic analysis showed that the predicted ScGluD2 protein was classified into subfamily D beta-1,3-glucanase. Localization of the ScGluD2 protein in the plasma membrane was determined by tagging it with green fluorescent protein. The expression of ScGluD2 was more up-regulated in sugarcane smut-resistant cultivars in the early stage (1 or 3 days) than in the susceptible ones after being challenged by the smut pathogen, revealing that ScGluD2 may be involved in defense against the invasion of Sporisorium scitamineum. Transient overexpression of ScGluD2 in Nicotiana benthamiana leaves induced a defense response and exhibited antimicrobial action on the tobacco pathogens Pseudomonas solanacearum and Botrytis cinerea, further demonstrating that ScGluD2 was related to the resistance to plant pathogens. However, the transcripts of ScGluD2 partially increased (12 h) under NaCl stress, and were steadily up-regulated from 6 to 24 h upon ABA, H2O2, and CdCl2 treatments, suggesting that ABA may be a signal molecule regulating oxidative stress and play a role in the salt and heavy metal stress-induced stimulation of ScGluD2 transcripts. Taken together, ScGluD2, a novel member of subfamily D beta-1,3-glucanase, was a stress-related gene of sugarcane involved in plant defense against smut pathogen attack and salt and heavy metal stresses.

Highlights

  • Plants generate pathogenesis-related (PR) proteins in response to pathogen infection

  • Reverse transcription-polymerase chain reaction (RT-PCR) with primers designed based on the gene sequence of S. bicolor beta1,3-glucanase (GenBank Acc No Sb02g037380) resulted in a full-length putative sugarcane beta-1,3-glucanase cDNA which was named as ScGluD2 (GenBank Acc No KF664181)

  • ScGluD2 transcript levels sharply increased from 12 to 48 h under CdCl2 treatment, increasing up to 1,260.22, 455.18, and 1,253.54-fold of that of the control. These results suggest that ScGluD2 is a stress-related gene, which positively responded to abscisic acid (ABA), H2O2, NaCl, and CdCl2 stimuli in sugarcane but was suppressed during salicylic acid (SA), methyl jasmonate (MeJA), and polyethylene glycol (PEG) treatments

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Summary

Introduction

Plants generate pathogenesis-related (PR) proteins in response to pathogen infection. The expression of beta1,3-glucanase genes has been shown to be regulated by certain environmental stresses, such as pathogen infection (Gu et al, 2008; Liu et al, 2010), wounding (Wu and Bradford, 2003), salt (Su et al, 2013), and plant hormone stimuli (Akiyama and Pillai, 2001; Wu and Bradford, 2003; Liu et al, 2010). Akiyama and Pillai (2001) have reported that the expression of an endo-1,3-beta-glucanase (OsGLN1) from rice was up-regulated by abscisic acid (ABA) and drought stress The expression of beta1,3-glucanase genes has been shown to be regulated by certain environmental stresses, such as pathogen infection (Gu et al, 2008; Liu et al, 2010), wounding (Wu and Bradford, 2003), salt (Su et al, 2013), and plant hormone stimuli (Akiyama and Pillai, 2001; Wu and Bradford, 2003; Liu et al, 2010). Liu et al (2010) detected the beta-1,3-glucanase gene, TaGlu, in wheat that was induced by the stripe rust pathogen Puccinia striiformis f. sp. tritici, salicylic acid (SA), methyl jasmonate (MeJA), and ethylene (ET). Gu et al (2008) demonstrated that the overexpression of tobacco chitinase I gene and the beta1,3-glucanase gene in sugarcane (Saccharum spp.) had different inhibitory efficiencies on the growth of the sugarcane smut pathogen (Sporisorium scitamineum). Wu and Bradford (2003) found that the GluB gene showed a tissue-specific regulation in tomato seeds and leaves, and its gene expression level was slightly up-regulated by MeJA and wounding during tomato seed germination. Akiyama and Pillai (2001) have reported that the expression of an endo-1,3-beta-glucanase (OsGLN1) from rice was up-regulated by abscisic acid (ABA) and drought stress

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