A novel groel gene from the endosymbiont of beet leafhopper, Candidatus Sulcia muelleri

Curtoviruses are transmitted by the beet leafhopper Circulifer tenellus, in a circulative (non-propagative) manner. Curtoviruses are phloem-limited and are acquired by the vector during feeding. Sap-feeding insects harbor endosymbionts which can help provide essential nutrients required for the insects’ survival. Candidatus Sulcia muelleri is an endosymbiont present in the beet leafhopper identified during this study. A housekeeping gene, groel, was identified from the endosymbiont. The groel gene sequence from this strain of Ca. S. muelleri differs from all other strains published in NCBI, suggesting the presence of a new strain, which was named S. muelleri beet leafhopper (SMBLH). A GroEL-homolog protein produced from groel was found in different vectors with circulative transmission. Analysis of nucleotide and translated sequences, using alignment, phylogenetic trees, and predicted secondary and tertiary structures showed that SMBLH GroHp has similarities to Escherichia coli GroEL and the GroEL-homolog proteins from Hamiltonella and Buchnera, endosymbionts of whiteflies and aphids, respectively. GroHp and GroEL were expressed as fusion proteins. Electron microscopy analyses indicate that purified expressed GroHp and GroEL proteins demonstrate correct folding.