Abstract
Insect herbivory can seriously hinder plant performance and reduce crop yield. Thrips are minute cell‐content‐feeding insects that are important vectors of viral plant pathogens, and are serious crop pests. We investigated the role of a sweet pepper (Capsicum annuum) lipoxygenase gene, CaLOX2, in the defense of pepper plants against Western flower thrips (Frankliniella occidentalis). This was done through a combination of in‐silico, transcriptional, behavioral and chemical analyses. Our data show that CaLOX2 is involved in jasmonic acid (JA) biosynthesis and mediates plant resistance. Expression of the JA‐related marker genes, CaLOX2 and CaPIN II, was induced by thrips feeding. Silencing of CaLOX2 in pepper plants through virus‐induced gene silencing (VIGS) resulted in low levels of CaLOX2 transcripts, as well as significant reduction in the accumulation of JA, and its derivatives, upon thrips feeding compared to control plants. CaLOX2‐silenced pepper plants exhibited enhanced susceptibility to thrips. This indicates that CaLOX2 mediates JA‐dependent signaling, resulting in defense against thrips. Furthermore, exogenous application of JA to pepper plants increased plant resistance to thrips, constrained thrips population development and made plants less attractive to thrips. Thus, a multidisciplinary approach shows that an intact lipoxygenase pathway mediates various components of sweet pepper defense against F. occidentalis.
Highlights
In nature, land plants and insects have coexisted for more than 400 million years
To narrow down the selection towards the specific LOX protein induced upon herbivory or wounding in sweet pepper, the closest homolog of the tomato LOXD gene, well-known to have a similar function (Yan et al 2013), was selected from pepper (CaLOX2, Capana03g000103) and further subjected to phylogenetic and synteny analysis
In the 13-type clade, the related pepper LOX2 protein is positioned in the sub-clade of LOX proteins within the Solanaceae family that are known to be involved in jasmonic acid (JA) biosynthesis
Summary
Plants perceive herbivorous insects by the specific pattern of tissue disruption and/or chemical cues originating from insects (Bonaventure 2012; Heidel-Fischer et al 2014). Plants have three main signal-transduction pathways, each involving a major plant hormone; i.e., jasmonic acid (JA), salicyclic acid (SA) and ethylene (ET), underlying induced defence against attackers such as herbivorous insects (Pieterse et al 2012; Stam et al 2014). The three major signaling pathways may exhibit crosstalk. JA and SA usually act antagonistically, but are reported to act synergistically, or additively (Pieterse et al 2012; Thaler et al 2012)
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