ARS | Publication request: Unconventional conservation among genes encoding small secreted salivary sland proteins from a gall midge

Submitted to: BMC Evolutionary Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 8, 2010
Publication Date: September 3, 2010
Citation: Chen, M., Liu, X., Zhao, H., Stuart, J.J., Shukle, R.H., Yang, Z., Hulbert, S. 2010. Unconventional conservation among genes encoding small secreted salivary sland proteins from a gall midge. BMC Evolutionary Biology. 10:296.

Interpretive Summary: Organisms adapt to environment changes through a range of genetic and epigenetic mechanisms. Various models have been developed to explain genetic adaptation and evolution based on genetic and epigenetic phenomena observed previously. During characterization of genes encoding small secretory salivary gland proteins (SSSGPs)of Hessian fly, we discovered an unconventional conservation pattern that is hard to be explained by current evolution models and theories. Within very short regions, there are tandem repeats containing multiple members of gene families that are highly diversified in coding regions, but highly conserved in the rest of the genes including introns. Sequence analysis suggested that diversifying selection was part of the mechanism for hyper-diversity in coding regions, whereas functional constraints were likely responsible for the conservation of the regulatory regions. However, other unknown genetic mechanisms were also likely involved in the genetics of these groups of genes. This report may provide a foundation for the discovery of new genetic mechanisms involved in gene evolution and functional adaptation.

Technical Abstract: Due to functional constraints associated with protein-coding sequences, introns and the 3’-untranslated region (UTR) of most genes vary the most, followed by the 5’-UTR. The coding region is the most conserved due to stronger functional constraints. During characterization of transcripts and genes encoding small secreted salivary gland proteins (SSSGPs) from the Hessian fly, we found the opposite pattern of conservation in several families of genes which appeared to have arisen from recent duplication events. The non-coding regions of these genes, including the 5’- and 3’-UTRs, and promoter regions and some introns were all highly conserved, but the coding regions were typically poorly conserved. The poor conservation of the coding regions made nucleotide sequence alignments difficult for some families except for the first ~60 bases, which were predicted to code for the secretion signal peptides. Discontinuity in regions of conservation of the genes suggests novel mechanisms for sequence homogenization that are still not understood. Strong diversifying selection was observed in the regions coding for mature proteins, whereas apparent stringent regulation of gene expression probably contributes to conservation in the promoter regions. The presence of a secretion peptide, predominant expression in salivary glands, and ability of some gene family members to respond to different plant genotypes indicated that they are likely effector proteins for insect virulence.