Differential Gene Expression Analysis in Polygonum Minus Leaf Upon 24H
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ORIGINAL RESEARCH published: 06 February 2017 doi: 10.3389/fpls.2017.00109 Differential Gene Expression Analysis in Polygonum minus Leaf upon 24 h of Methyl Jasmonate Elicitation Reyhaneh Rahnamaie-Tajadod *, Kok-Keong Loke, Hoe-Han Goh and Normah M. Noor Institute of Systems Biology (INBIOSIS), Universiti Kebangsaan Malaysia, Bangi, Malaysia Polygonum minus is an herbal plant that grows in Southeast Asian countries and traditionally used as medicine. This plant produces diverse secondary metabolites such as phenolic compounds and their derivatives, which are known to have roles in plant abiotic and biotic stress responses. Methyl jasmonate (MeJA) is a plant signaling molecule that triggers transcriptional reprogramming in secondary metabolism and activation of defense responses against many biotic and abiotic stresses. However, the effect of MeJA elicitation on the genome-wide expression profile in the leaf tissue of P. minus has not been well-studied due to the limited genetic information. Hence, we Edited by: performed Illumina paired-end RNA-seq for de novo reconstruction of P. minus leaf Rajeev K. Varshney, International Crops Research Institute transcriptome to identify differentially expressed genes (DEGs) in response to MeJA for the Semi-Arid Tropics, India elicitation. A total of 182,111 unique transcripts (UTs) were obtained by de novo assembly Reviewed by: of 191.57 million paired-end clean reads using Trinity analysis pipeline. A total of 2374 UTs Michael Deyholos, University of British Columbia, Canada were identified to be significantly up-/down-regulated 24 h after MeJA treatment. These Gunvant Baliram Patil, UTs comprising many genes related to plant secondary metabolite biosynthesis, defense University of Missouri, USA and stress responses. To validate our sequencing results, we analyzed the expression of Jianfei Zhao, University of Pennsylvania, USA 21 selected DEGs by quantitative real-time PCR and found a good correlation between *Correspondence: the two analyses. The single time-point analysis in this work not only provides a useful Reyhaneh Rahnamaie-Tajadod genomic resource for P.minus but also gives insights on molecular mechanisms of stress [email protected] responses in P. minus. Specialty section: Keywords: differentially expressed gene, de novo transcriptome, Illumina sequencing, elicitation, Persicaria minor This article was submitted to Plant Genetics and Genomics, a section of the journal INTRODUCTION Frontiers in Plant Science Received: 21 June 2016 Due to the sessile lifestyle, plants have to cope with different changes of biotic/abiotic factors in Accepted: 19 January 2017 their surrounding environments to survive in nature. However, this defense response is costly and Published: 06 February 2017 often setback by the repression of growth (Yang et al., 2012b). In response to stresses, plants convert Citation: resource allocation from growth to the biosynthesis of defensive compounds which is energetically Rahnamaie-Tajadod R, Loke K-K, demanding (Attaran et al., 2014). Plants produce a wide range of secondary metabolites for Goh H-H and Noor NM (2017) coordinated plant response to various internal and external cues (Davies and Schwinn, 2003). Plant Differential Gene Expression Analysis in Polygonum minus Leaf upon 24 h of secondary metabolites comprise a large group of lipophilic volatile organic compounds (VOCs) Methyl Jasmonate Elicitation. with high vapor pressure and low molecular weight. VOCs serve as signal molecules to mediate Front. Plant Sci. 8:109. plant communication with their environment for herbivore deterrence, attraction of pollinators, doi: 10.3389/fpls.2017.00109 seed dispersers, and protection against different stresses (Dudareva et al., 2013). Frontiers in Plant Science | www.frontiersin.org 1 February 2017 | Volume 8 | Article 109 Rahnamaie-Tajadod et al. MeJA-Regulated DEGs in P. minus Leaf Beside their main role in defending plants from (Vikram et al., 2014). Hence, it has a great potential for various environmental stresses, investigations on the biosynthesis applications in the pharmaceutical and perfumery industries for of VOCs have also attracted much interest for their applications its essential oil. as pharmaceuticals, pesticides, fragrance, and flavoring (Crozier Previously, an elicitation experiment using MeJA was et al., 2008). However, due to low abundance of these secondary performed on P. minus leaves through cDNA-amplified fragment metabolites (<1% dry weight) and high industrial demands, length polymorphism (AFLP) transcript profiling approach with some plants in the wild which produce valuable compounds are reported effects on some of the genes involved in secondary overharvested and exposed to endangerment (Yang et al., 2014). metabolite biosynthesis (Ee et al., 2013). However, detailed Therefore, a comprehensive knowledge of metabolic pathways understanding of the biological mechanism of MeJA-mediated and regulatory mechanisms involved in the biosynthesis of production of secondary metabolites and whole transcriptome VOCs is necessary to understand their role in defense responses changes was incomplete due to limitations in the gel-based and to enhance their yields for various applications. selection of cDNA-AFLP transcripts for sequencing. Increased accumulation of volatile secondary metabolites in To date, there are only 3352 expressed sequence tags (ESTs) plants leads to enhanced stress tolerance and the activation of of P. minus available in the NCBI database from previous defense mechanisms (Aranega-Bou et al., 2014). A multilevel study (Roslan et al., 2012). In the current study, we aim to network of biosynthesis pathways and regulation of secondary identify differentially expressed genes (DEGs) in the MeJA- metabolites converges on complex hormone signaling cascades elicited P. minus leaf at 24 h compared with mock treatment. in which jasmonates (JAs) play a crucial role in transcriptional To gain an in-depth knowledge of gene expression changes in control of plant defense gene expression and metabolism MeJA-elicited leaves, RNA-seq was employed to greatly expand (Attaran et al., 2014). the genomic resources (Loke et al., 2016). Over 192 million JAs consisting jasmonic acid (JA) and its cyclopentanon short pair-end reads were generated by Illumina HiSeqTM 2000 derivatives such as its volatile methyl ester (methyl jasmonate, platform and used for de novo transcriptome assembly through MeJA), are plant-specific endogenous signaling phytohormones Trinity analysis pipeline. The assembled UTs were analyzed that have long been observed to be potent regulators of elicitor to identify DEGs for functional annotation and downstream signals for the biosynthesis of plant secondary metabolites (Zhao analyses. This is the first report on genome-wide transcriptional et al., 2005). This endogenous hormone regulates a variety of response in P. minus leaf elicited by MeJA with a focus physiological plant processes such as root elongation, vegetative on the biosynthesis of secondary metabolites. Furthermore, growth, production of viable pollen, senescence, cell cycle understanding the molecular mechanisms underlying MeJA regulation, fruit ripening, production of specialized metabolites, elicitation will assist in genetic engineering of targeted secondary plant response to wounding and defenses against pathogens, metabolites in P. minus. insects, and notorious pests (Farmer et al., 2003). It is well- studied that elicitation is a common method of inducing the MATERIALS AND METHODS accumulation of plant defensive secondary metabolites in whole plant or cell culture (Memelink et al., 2001). Previous genome- Plant Materials and MeJA Treatment wide transcript profiling studies revealed that the addition of P. minus stem cuttings were collected from Genting Highland (3◦ JA elicitors such as MeJA induces an extensive transcriptional 25′ 42.18′′ N, 101◦ 47′ 21.45′′ E) and propagated in controlled reprogramming (De Geyter et al., 2012) leading to activation environment chambers (A1000, Conviron, Canada) at 22/16◦C of several metabolic pathways including terpenoids (Misra day/night temperatures under 12 h light/dark photoperiod with et al., 2014), phenylpropanoids (Cocetta et al., 2015), and light intensity of 170 ± 20 µmol m−2 s−1 at ∼75% RH. After alkaloids (Kang et al., 2004). In addition to defense induction, 45 days (Khairudin et al., 2014), an aqueous solution of 150 the exogenous MeJA elicitation affects other plant functions µM MeJA (Sigma-Aldrich) (Ismail et al., 2011) and 0.01% (v/v) including ontogeny, vegetative growth, and photosynthesis Tween 20 was sprayed on all plant leaves to the point of runoff. (Moreira et al., 2009). Previous studies showed that exogenous The control (mock-treated) plant leaves were sprayed with only application of MeJA induces defense responses and reduces 0.01% (v/v) Tween 20. After elicitation, treated and control plants growth in several species (Heijari et al., 2005; Nabity et al., 2012; were placed separately in different growth chambers. Expanded Yang et al., 2012b; Noir et al., 2013; Attaran et al., 2014). young leaves from apical parts of plants (Ee et al., 2013) were Polygonum minus Huds (syn. Persicaria minor), commonly harvested at 24 h after treatment and immediately frozen in liquid known as “kesum” in Malaysia, is an aromatic herbal plant in nitrogen before storage at −80◦C. Two biological replicates from the Polygonaceae family which is widely used as a flavoring independent control and treated plants were prepared for