Cell-wall-degrading enzymes produced in vitro and in vivo by Rhizoctonia solani, the causative fungus of peanut sheath blight.

Ru Jun Zhou,Jun Fan Fu,Cai Yun Xue,Yuan Jie Li,Di Xiao

doi:10.7717/peerj.5580

Abstract

Rhizoctonia solani causes the disease peanut sheath blight, involving symptoms of maceration and necrosis of infected tissue, mainly caused by cell-wall-degrading enzymes (CWDEs). This study investigated the production of CWDEs including polygalacturonase (PG), polymethyl-galacturonase (PMG), cellulase (Cx) and β-glucosidase by R. solani in vitro (in liquid culture) and in vivo (in peanut plants). Significant PG, PMG, Cx and β-glucosidase activities were detected in infected tissues including stalk and leaves of Baisha and Silihong peanut cultivars. Extracts of healthy tissue showed little or no such activities. In shaken liquid cultures of R. solani in medium containing pectin or pectin plus carboxymethyl cellulose (CMC) as the carbon source(s), PG and PMG were notably active. Significant Cx activity was detected in cultures with CMC or pectin plus CMC as the carbon source(s). However, only a very low level of β-glucosidase activity was observed in cultures with any of the tested carbon sources. An increase of pH was recorded in decayed peanut tissues and liquid culture filtrates; the filtrate pH and fungal growth positively correlated. The fungal growth and/or pH were important factors for the production of PG, PMG and Cx in culture with pectin plus CMC as the carbon source. A single active PG isozyme with isoelectric point around 9.2 was detected in culture filtrates and in infected peanut tissues by the method of isoelectric focusing electrophoresis. The crude enzymes extracted from liquid culture of R. solani induced decay of healthy peanut leaves.

Highlights

IntroductionMost plant fungal pathogens produce a wide range of cell-wall-degrading enzymes (CWDEs) (Zhang et al, 1999; Lalaoui et al, 2000; Gao et al, 2000; Brien & Zamani, 2003; Yang et al, 2012b; Li et al, 2012; Zhao et al, 2014; Zhang, Bruton & Biles, 2014; Amit et al, 2014)
The results indicated that PG activity was induced in the three media; the highest amount of PG activity was produced in the medium containing pectin plus carboxymethyl cellulose (CMC), followed by medium with pectin as the sole carbon source, and low activity was produced in CMC-containing medium
The present study provided the first evidence that cell-wall-degrading enzymes (CWDEs) are produced by R. solani in peanut sheath blight and that they are likely responsible for the death and maceration of infected tissue

Summary

Introduction

Most plant fungal pathogens produce a wide range of cell-wall-degrading enzymes (CWDEs) (Zhang et al, 1999; Lalaoui et al, 2000; Gao et al, 2000; Brien & Zamani, 2003; Yang et al, 2012b; Li et al, 2012; Zhao et al, 2014; Zhang, Bruton & Biles, 2014; Amit et al, 2014). It has been demonstrated histochemically and histopathologically that the disintegration and change of plant cell walls is due to CWDEs (Weinhold & Motta, 1973; Fehrmann & Mendgen, 1975; Wanjiru, Kang & Buchenauer, 2002; Kang et al, 2007). PMG shows high activity in culture and in host tissue inoculated with many fungal pathogens and has been determined to be a virulence factor (Gao et al, 2000; Li et al, 2003, 2012; Chen et al, 2006; Dong et al, 2010; Yang et al, 2012b; Zhou et al, 2016)

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Discussion

Conclusion