Abstract
Key messageLipoxygenases mediate important biological processes. Through comparative genomics, domain-scan analysis, sequence analysis, phylogenetic analysis, homology modelling and transcriptional analysis the lipoxygenase gene family of pepper (Capsicum annuum) has been identified.Lipoxygenases (LOXs) are non-heme, iron-containing dioxygenases playing a pivotal role in diverse biological processes in plants, including defence and development. Here, we exploited the recent sequencing of the pepper genome to investigate the LOX gene family in pepper. Two LOX classes are recognized, the 9- and 13-LOXs that oxygenate lipids at the 9th and 13th carbon atom, respectively. Using two main in-silico approaches, we identified a total of eight LOXs in pepper. Phylogenetic analysis classified four LOXs (CaLOX1, CaLOX3, CaLOX4 and CaLOX5) as 9-LOXs and four (CaLOX2, CaLOX6, CaLOX7 and CaLOX8) as 13-LOXs. Furthermore, sequence similarity/identity and subcellular localization analysis strengthen the classification predicted by phylogenetic analysis. Pivotal amino acids together with all domains and motifs are highly conserved in all pepper LOXs. Expression of 13-LOXs appeared to be more dynamic compared to 9-LOXs both in response to exogenous JA application and to thrips feeding. Bioinformatic and expression analyses predict the putative functions of two 13-LOXs, CaLOX6 and CaLOX7, in the biosynthesis of Green Leaf Volatiles, involved in indirect defence. The data are discussed in the context of LOX families in solanaceous plants and plants of other families.
Highlights
Lipoxygenases (EC 1.13.11.12) are non-heme, iron-containing dioxygenases ubiquitously present in plants, animals and fungi (Brash 1999)
green leaf volatiles (GLVs) play a pivotal role in the attraction of natural enemies of the herbivores
To investigate the role of pepper LOXs in defence mechanisms, we examined their expression upon two treatments: exogenous jasmonic acid (JA) application and exposure to feeding by a natural inducer of JA, the cell-content feeding insect Western flower thrips (WFT)
Summary
Lipoxygenases (EC 1.13.11.12) are non-heme, iron-containing dioxygenases ubiquitously present in plants, animals and fungi (Brash 1999). Upon insect or pathogen attack, LOXs oxidize polyunsaturated fatty acids (PUFAs) (linoleic acid, α-linolenic acid and arachidonic acid) constituting a (Z,Z)-1,4-pentadiene structural unit and catalyzing it into conjugated hydro-peroxides such as oxylipins (Brash 1999; Feussner and Wasternack 2002; Shibata and Axelrod 1995) Oxylipins such as jasmonates, green leaf volatiles (GLVs) and recently discovered death acids, are known for their roles in defence against herbivorous insects and pathogens (Allmann et al 2010; Bell et al 1995; Christensen et al 2015; Losvik et al 2017; Shen et al 2014; Yan et al 2013). The resulting data provide insights into putative functions of these genes in pepper
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