Genes of the de novo and Salvage Biosynthesis Pathways of Vitamin B6 are Regulated under Oxidative Stress in the Plant Pathogen Rhizoctonia solani.

Jamil Samsatly,Emile Gluck-Thaler,Rony Chamoun,Suha Jabaji

doi:10.3389/fmicb.2015.01429

Jamil Samsatly, Emile Gluck-Thaler + Show 2 more

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https://doi.org/10.3389/fmicb.2015.01429

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Abstract

Vitamin B6 is recognized as an important cofactor required for numerous metabolic enzymes, and has been shown to act as an antioxidant and play a role in stress responses. It can be synthesized through two different routes: salvage and de novo pathways. However, little is known about the possible function of the vitamin B6 pathways in the fungal plant pathogen Rhizoctonia solani. Using genome walking, the de novo biosynthetic pathway genes; RsolPDX1 and RsolPDX2 and the salvage biosynthetic pathway gene, RsolPLR were sequenced. The predicted amino acid sequences of the three genes had high degrees of similarity to other fungal PDX1, PDX2, and PLR proteins and are closely related to other R. solani anastomosis groups. We also examined their regulation when subjected to reactive oxygen species (ROS) stress inducers, the superoxide generator paraquat, or H2O2, and compared it to the well-known antioxidant genes, catalase and glutathione-S-transferase (GST). The genes were differentially regulated with transcript levels as high as 33 fold depending on the gene and type of stress reflecting differences in the type of damage induced by ROS. Exogenous addition of the vitamers PN or PLP in culture medium significantly induced the transcription of the vitamin B6 de novo encoding genes as early as 0.5 hour post treatment (HPT). On the other hand, transcription of RsolPLR was vitamer-specific; a down regulation upon supplementation of PN and upregulation with PLP. Our results suggest that accumulation of ROS in R. solani mycelia is linked to transcriptional regulation of the three genes and implicate the vitamin B6 biosynthesis machinery in R. solani, similar to catalases and GST, as an antioxidant stress protector against oxidative stress.

Highlights

Vitamin B6 is a collective term that refers to a group of six vitamers: pyridoxal (PL), pyridoxine (PN), pyridoxamine, and their phosphorylated derivatives (PLP, PNP, PMP) (Fitzpatrick et al, 2012; Vanderschuren et al, 2013)
With the aim of gaining insight into the possible implication of reactive oxygen species (ROS) on vitamin B6 regulation in R. solani, we report on the characterization of three vitamin B6 genes, RsolPDX1, and RsolPDX2 from the vitamin B6 de novo pathway and RsolPLR from the salvage pathway
PCR products for each of the three genes were assembled into contigs and their sequence analysis led to the identification of the vitamin B6 genes belonging to the de novo pathway in R. solani, RsolPDX1, and RsolPDX2, and to a identification of RsolPLR belonging to the vitamin B6 salvage pathway

Summary

Introduction

Vitamin B6 is a collective term that refers to a group of six vitamers: pyridoxal (PL), pyridoxine (PN), pyridoxamine, and their phosphorylated derivatives (PLP, PNP, PMP) (Fitzpatrick et al, 2012; Vanderschuren et al, 2013). The antioxidant properties of vitamin B6 was originally reported in the fungal pathogen Cercospora nicotianae, by providing resistance to cercosporin, a singlet oxygen generating toxin (Ehrenshaft et al, 1999; Bilski et al, 2000; Daub and Ehrenshaft, 2000). This novel characteristic of vitamin B6 as a ROS scavenger and its ability to increase resistance to biotic and abiotic stresses have been demonstrated in plant-microbe interaction studies (Danon et al, 2005; Denslow et al, 2005). Supplementation with PM could delay or decrease pathogen-induced leaf necrosis (Denslow et al, 2005) while PN could protect Arabidopsis flu mutant, which releases singlet oxygen in plastids, from cell death (Danon et al, 2005)

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