Abstract
Plant sap-feeding hemipterans harbor obligate symbiotic microorganisms which are responsible for the synthesis of amino acids missing in their diet. In this study, we characterized the obligate symbionts hosted in the body of the xylem-feeding leafhopper Evacanthus interruptus (Cicadellidae: Evacanthinae: Evacanthini) by means of histological, ultrastructural and molecular methods. We observed that E. interruptus is associated with two types of symbiotic microorganisms: bacterium ‘Candidatus Sulcia muelleri’ (Bacteroidetes) and betaproteobacterium that is closely related to symbionts which reside in two other Cicadellidae representatives: Pagaronia tredecimpunctata (Evacanthinae: Pagaronini) and Hylaius oregonensis (Bathysmatophorinae: Bathysmatophorini). Both symbionts are harbored in their own bacteriocytes which are localized between the body wall and ovaries. In E. interruptus, both Sulcia and betaproteobacterial symbionts are transovarially transmitted from one generation to the next. In the mature female, symbionts leave the bacteriocytes and gather around the posterior pole of the terminal oocytes. Then, they gradually pass through the cytoplasm of follicular cells surrounding the posterior pole of the oocyte and enter the space between them and the oocyte. The bacteria accumulate in the deep depression of the oolemma and form a characteristic ‘symbiont ball’. In the light of the results obtained, the phylogenetic relationships within modern Cicadomorpha and some Cicadellidae subfamilies are discussed.
Highlights
The Hemiptera are a large group of insects with feeding habits that range from phytophagy to predation, including ectoparasitism and hematophagy (Forero 2008)
Molecular identification and phylogenetic analysis of symbionts of Evacanthus interruptus The systematic affinity of bacteriome-associated symbionts of E. interruptus from both Polish and Ukrainian populations was determined based on the analysis of their 16S rDNA sequences
A comparison of the obtained 16S rDNA sequences of Sulcia symbionts from Polish and Ukrainian populations of E. interruptus indicated that they are identical, whereas there is a slight difference between the 16S rDNA sequences of betaproteobacterial symbionts (1 %)
Summary
The Hemiptera are a large group of insects with feeding habits that range from phytophagy to predation, including ectoparasitism and hematophagy (Forero 2008). Plant feeders suck the phloem or xylem sap, or ingest plant cell content (Backus 1988; Campbell et al 1994; Sorensen et al 1995). Among the six suborders of the Hemiptera (i.e. Paleorrhyncha, Sternorrhyncha, Fulgoromorpha, Cicadomorpha, Coleorrhyncha and Heteroptera; Szwedo et al 2004; Grimaldi and Engel 2005; Drohojowska et al 2013), the Cicadomorpha: Clypeata lineage (uniting extinct Hylicelloidea and extant Cicadoidea, Cercopoidea and Membracoidea sensu lato) is the only one with several strong adaptations for xylem feeding (Wang et al 2012), in some of them shifts to cell-content and back to phloem feeding occurred (Dietrich 2013). Most plant sup-sucking hemipterans live in mutualistic associations with symbiotic microorganisms (bacteria or yeast) which synthesize missing nutrients and provide them to their hosts (Wilkinson and Ishikawa 2001; Baumann 2005; Douglas 2009). The sequencing of the genome of bacteria inhabiting the body of hemipterans has indicated that these microorganisms possess the biosynthetic pathways necessary for the synthesis of essential amino acids, i.e. leucine, serine, tryptophan as well as many vitamins and other cofactors (Douglas 2006; Wu et al 2006; McCutcheon and Moran 2007; McCutcheon et al 2009)
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