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

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

JOURNAL=Frontiers in Microbiology

VOLUME=6

YEAR=2016

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2015.01429

DOI=10.3389/fmicb.2015.01429

ISSN=1664-302X

ABSTRACT=<p>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 <italic>de novo</italic> pathways. However, little is known about the possible function of the vitamin B6 pathways in the fungal plant pathogen <italic>Rhizoctonia solani</italic>. Using genome walking, the <italic>de novo</italic> biosynthetic pathway genes; <italic>RsolPDX1</italic> and <italic>RsolPDX2</italic> and the salvage biosynthetic pathway gene, <italic>RsolPLR</italic> 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 <italic>R. solani</italic> anastomosis groups. We also examined their regulation when subjected to reactive oxygen species (ROS) stress inducers, the superoxide generator paraquat, or H<sub>2</sub>O<sub>2</sub>, and compared it to the well-known antioxidant genes, <italic>catalase</italic> and <italic>glutathione-S-transferase</italic> (<italic>GST</italic>). 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 <italic>de novo</italic> encoding genes as early as 0.5 hour post treatment (HPT). On the other hand, transcription of <italic>RsolPLR</italic> was vitamer-specific; a down regulation upon supplementation of PN and upregulation with PLP. Our results suggest that accumulation of ROS in <italic>R. solani</italic> mycelia is linked to transcriptional regulation of the three genes and implicate the vitamin B6 biosynthesis machinery in <italic>R. solani</italic>, similar to <italic>catalases</italic> and <italic>GST</italic>, as an antioxidant stress protector against oxidative stress.</p>