Vitamin B6 biosynthetic genes expression and antioxidant enzyme properties in tomato against, Erwinia carotovora subsp. carotovora Murugesan Chandrasekaran a, ⁎, Se Chul Chun b a Department of Food Science and Biotechnology, Sejong University, 209 Neungdong-ro, Gwangjin-gu, Seoul 05006, Republic of Korea b Department of Bioresource and Food Science, Konkuk University, Gwangjin-gu, Seoul, Republic of Korea abstract article info Article history: Received 8 January 2018 Received in revised form 4 May 2018 Accepted 4 May 2018 Available online 05 May 2018 Vitamin B6 (VitB6) is an essential cofactor for N140 biochemical reactions. Also, VitB6 is a potent antioxidant and helps plants cope with both biotic and abiotic stress conditions. However, the role of VitB6 in plant disease resis- tance has yet to be confirmed using molecular biology approaches. Here, we analyzed the expression patterns of VitB6 biosynthetic genes, including the de novo (PDX1 [PDX1.2 and 1.3] and PDX2) and the salvage (SOS4) path- ways during the response to Erwinia carotovora subsp. carotovora. By quantitative PCR, we found that the most significant upregulation in the transcript profile of PDX2, which showed a 9.2-fold increase in expression at 12 h post inoculation (hpi) compared to 24–48 hpi. We also detected significant upregulation of PDX1.2 and PDX1.3, which were 6.6- and 4.3-fold upregulated at 24 hpi compared to 12 hpi, while SOS4 showed only low- level expression. Also, at 24 hpi, a significant increase in superoxide dismutase, catalase, peroxidase, and polyphe- nol oxidase activities was observed in plants. Our findings confirm that the expression of de novo and salvage pathway genes is induced by E. carotovora and that this plays an important role in the regulation of defense re- sponse by modulating cellular antioxidant capacity. © 2018 Elsevier B.V. All rights reserved. Keywords: Erwinia carotovora Vitamin B6 Antioxidant enzymes Tomato Plant defense 1. Introduction A vitamin is defined as an organic compound required in limited amounts by an organism, including human that cannot produce it and thus needs to take it up with the diet. The vitamin B complex comprises water-soluble cofactors and their derivatives that are essential contrib- utors to diverse metabolic processes in plants, animals, and microorgan- isms [1]. Vitamin B6 (further referred to as VitB6) is a highly versatile cofactor that is required for N140 different biochemical reactions in the cell, primarily associated with amino acid metabolism [2,3]. It is most important for its contribution to amino acid biosynthesis where it serves as a cofactor for enzymes involved in decarboxylation, trans- amination, deamination, racemization and trans sulfuration [2,4]. VitB6 comprises a group of three chemically related compounds, pyri- doxine (PN), pyridoxamine (PM), and pyridoxal (PL), which differ in their 4′-position by having either a hydroxyl, an amino, or an aldehyde group, respectively [2]. To function as active cofactors they need to be phosphorylated at their 5′-position. In plants, two different pathways are known to synthesize VitB6. First, the de novo biosynthetic pathway is well resolved and involves the determined activities of the pyridoxine biosynthesis proteins PDX1 and PDX2, that form a multimeric protein complex to synthesize pyridoxal-5′-phosphate (PLP) as an active cofac- tor [5,6]. Second, the salvage pathway is a recovery pathway that con- verts PN, PL, or PM to the active cofactor PLP by the concerted activities of two enzymes, pdxH and pdxK, a VitB6 oxidase and a VitB6 kinase, re- spectively. PL is converted to PLP by a PN/PL/PM kinase (PDXK), while synthesis of PLP from PN and PM requires the additional activity of a PNP/PMP oxidase PDX3 [2,7]. Recently, PDX1 and PDX2 homologs from plants have been isolated and characterized [8,9,10]. Despite this evidence, the effect of VitB6 on plant development, the mechanisms controlling its biosynthesis and stress tolerance are still poorly understood. In addition, VitB6 is a potent antioxidant and helps plants cope with both biotic and abiotic stress conditions [3,7,8,and 11]. In A. thaliana, mutations at AtPDX1 genes led to increased sensitivity to salt, osmotic, and high light stress [8,12,13] whereas overexpression of PDX gene resulted in increased tolerance to oxidative stress [10,14]. During these abiotic stress responses, it was shown that VitB6 vitamers are efficient quenchers of both singlet oxy- gen and superoxide anions [9,15]. Moreover, Denslow et al. [9] and Sivasubramanian et al. [16] showed that salicylic acid, methyl jasmonate, and ethylene, chemical inducers of oxidative plant defense responses, increase PDX transcript in N. tabacum and Hevea brasiliensis. Expression of the PDX genes was induced in to- bacco plants after treatment with signaling molecules but was de- creased after inoculation with an incompatible pathogen, Pseudomonas syringae pv. phaseolicola [9]. Also, pyridoxine delayed and attenuated International Journal of Biological Macromolecules 116 (2018) 31–36 ⁎ Corresponding author at: Department of Food Science and Biotechnology, Sejong University, Seoul, Republic of Korea. E-mail address: chandrubdubio@gmail.com (M. Chandrasekaran). https://doi.org/10.1016/j.ijbiomac.2018.05.024 0141-8130/© 2018 Elsevier B.V. All rights reserved. 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