Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 6/26/2013
Publication Date: N/A
Technical Abstract: Biosynthesis of 20-hydroxyecdysone (20E) in insects involves the action of five cytochrome P450s collectively known as Halloween genes. The complete transcripts of 3 Halloween genes [spook (Vdspo), disembodied (Vddib) and shade (Vdshd)] from the varroa mite were identified, sequenced and mapped to their genomic sequences. As compared with spook from insects and crustacean which have a maximum of 2 introns, Vdspo contained 5 introns ranging from 166 to 1479 bp. Both, Vddib and Vdshd contained 8 introns. A phylogenetic analysis revealed these 3 Halloween genes derived from common ancestoral genes. Phantom and shadow orthologs have not been identified in the varroa genome. Similarly, phantom orthologs have not been identified in the spider mite Tetranychus urticae or the deer tick Ixodes scapularis genomes, but both acarine genomes contained shadow orthologs. Predicted amino acid sequences from Vdspo, Vddib and Vdshd coding regions shared 33.3, 32.1 and 29.6% identity with the Drosophila melanogaster orthologs, respectively. Vddib transcript was present in ovary/lyrate organ samples while Vdshd transcript was present in ovary/lyrate organ, Malpighian tubules and gut samples. Vdspo transcript was detected only in gut samples and remained at constant levels in phoretic and early reproductive mites (from pre-capping brood cells). The Vdspo transcript levels in phoretic mites were 7.8 and 7 times higher than those of Vddib and Vdshd, respectively. In contrast to Vdspo, Vddib and Vdshd transcript levels were significantly up-regulated by 1.87 and 2.05 fold in early reproductive mites when compared to phoretic mites. A brood cell invasion assay showed that transcript levels from Vdspo, Vddib and Vdshd were not significantly different between mites that entered a brood cell within 4 hr compared to mites that remained on adult bees. LC-MS analysis of the hemolymph from various honey bee stages and whole body phoretic mites revealed a high abundance of putative diketol (intermediate in the 20E biosynthesis) in all samples, but none had detectable levels of 20E. These results suggest that the expression of Vddib and Vdshd is not related with the initiation of the varroa mite brood cell invasion behavior, but is associated to the physiological shift from phoretic to reproductive mite.