Abstract
BackgroundRecent studies show that galling Hymenoptera and Diptera are able to synthesize the plant hormone indole-3-acetic acid (auxin) from tryptophan and that plant response to insect-produced auxin is implicated in gall formation. We examined the leaf transcriptome of galled and ungalled leaves of individuals of the Hawaiian endemic plant Metrosideros polymorpha (Myrtaceae) subject to infestation by psyllid (Hemiptera) gall-makers in the genus Trioza (Triozidae).ResultsTranscript libraries were sequenced using Illumina technology and the reads assembled de novo into contigs. Functional identification of contigs followed a two-step procedure, first identifying contigs by comparison to the completely sequenced genome of the related Eucalyptus, followed by identifying the equivalent Arabidopsis gene using a pre-computed mapping between Eucalyptus and Arabidopsis genes. This allowed us to use the rich functional annotation of the Arabidopsis genome to assess the transcriptional landscape of galling in Metrosideros. Comparing galled and ungalled leaves, we find a highly significant enrichment of expressed genes with a gene ontology (GO) annotation to auxin response in the former. One gene consistently expressed in all galled trees examined but not detected in any libraries from ungalled leaves was the Metrosideros version of SMALL AUXIN UPREGULATED (SAUR) 67 which appears to be a marker for leaf-galling in Metrosideros.ConclusionsWe conclude that an auxin response is involved in galling by Metrosideros psyllids. The possibility should therefore be considered that psyllids (like other insects examined) are able to synthesize auxin.
Highlights
Recent studies show that galling Hymenoptera and Diptera are able to synthesize the plant hormone indole-3-acetic acid from tryptophan and that plant response to insect-produced auxin is implicated in gall formation
The biology of galls - what is known? A gall is a plant structure resulting from the alteration of plant developmental processes by a galling organism, and which increases the fitness of the galler by providing a nutrient rich, protected environment [1]
To assess whether the over-representation of auxin response genes is general in galled leaves, we examined pairwise comparisons of all galled samples vs all ungalled samples using all genotypes (Table 4)
Summary
Recent studies show that galling Hymenoptera and Diptera are able to synthesize the plant hormone indole-3-acetic acid (auxin) from tryptophan and that plant response to insect-produced auxin is implicated in gall formation. We examined the leaf transcriptome of galled and ungalled leaves of individuals of the Hawaiian endemic plant Metrosideros polymorpha (Myrtaceae) subject to infestation by psyllid (Hemiptera) gall-makers in the genus Trioza (Triozidae). A gall is a plant structure resulting from the alteration of plant developmental processes by a galling organism, and which increases the fitness of the galler by providing a nutrient rich, protected environment [1]. It can be considered an extension of the phenotype of the galling organism [2]. A diverse array of insects form galls, in the Hymenoptera, Diptera and Hemiptera [10]. The subject of this paper is a radiation of psyllid gall-makers on the common native Hawaiian tree, Metrosideros polymorpha
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