Adaptive evolution of peptidoglycan recognition protein family regulates the innate signaling against microbial pathogens in vertebrates

The innate immune system is the first line of defense in vertebrates against microbial pathogens. This defense system depends on the peptidoglycan pathogen recognition of receptors (PGRPs) existing in both invertebrates and vertebrates. Although some studies revealed the structural and functional differences between them, however, the evolutionary history and the selection pressures on these genes during adaptive evolution are poorly understood. In this study, we examined four (PGLYRP1, PGLYRP2, PGLYRP3, and PGLYRP4) genes of 127 vertebrates' species, conserved across vertebrates to evaluate positive selection pressure drives by adaptive evolution. The codons under positive selection were recognized through likelihood tests by comparing different models based on ω ratios in these genes across the vertebrate species. The positive selection test used two sets of models M1a vs. M2a and M7 vs. M8. The results showed that the test of these genes in M1a vs. M2a was not significant with the likelihood value 2ΔlnL = 0, while the likelihood ratios (2ΔlnL) were 2ΔlnL = 12.386, 2ΔlnL = 4.9283, 2ΔlnL = 24.031, and 2ΔlnL = 103.39 for PGLYRP1, PGLYRP2, PGLYRP3, and PGLYRP4 in M7 vs. M8, respectively. Our study identified the evidence of robust positive selection for these four genes across the vertebrates. These protuberant changes in PGRPs evolution of vertebrates reveal their role in innate immunity. Our study provides an insight based on PGRP genes to understand the evolution of host and pathogens interaction that leads to the progress of the novel conducts for immune diseases that include proteins linked to the recognition of pathogens.

Evidence of adaptive evolution of alpine pheasants to high-altitude environment from mitogenomic perspective

Adaptive evolutions to high-altitude adaptation have been intensively studied in mammals. However, considering the additional vertebrate groups, new perception regarding selection challenged by high-altitude stress on mitochondrial genome can be gained. To test this hypothesis, we compiled and analyzed the mitochondrial genomes of 5 alpine pheasants and 12 low-altitude species in Phasianidae. The results that evolutionary rates of ATP6 and ND6 showing significant fluctuation among branches when involved with five alpine pheasants revealed both genes might have implications with adapting to highland environment. The radical physico-chemical property changes identified by the modified MM01 model, including composition (C) and equilibrium constant (ionization of COOH) (Pk') in ATP6 and beta-structure tendencies (Pβ), Pk', and long-range non-bonded energy (El) in ND6, suggested that minor overall adjustments in size, protein conformation and relative orientation of reaction interfaces have been optimized to provide the ideal environments for electron transfer, proton translocation and generation of adenosine triphosphate (ATP). Additionally, three unique substitution sites were identified under selection in ND6, which could be potentially important adaptive changes contributing to cellular energy production. Our findings suggested that adaptive evolution may occur in alpine pheasants, which are an important complement to the knowledge of genetic mechanisms against the high-altitude environment in non-mammal animals.