It had long been known that Alfin-like (AL) proteins play important roles in regulating signals of plant salt tolerance. The AL transcription factor is a two-domain protein with the ability to bind to the highly methylated forms of histones and functions in plant salt tolerance. Previous work has shown that the co-evolution might have taken place among the protein family members which have more than two domains.
Researchers from Ecological Evolution Group of Xishuangbanna Tropical Botanical Garden (XTBG) examined the molecular evolution of the Alfin-like (AL) proteins in two Arabidopsis species (A. lyrata and A. thaliana) and a salt-tolerant close relative Thellungiella halophila. A phylogenetic tree was constructed to evaluate the evolutionary relationships of all observed AL genes and evidence for gene duplication and loss events was examined.
The researchers computed synonymous substitution ratios (dn/ds) and codon usage statistics to detect positive selection and where it might have occurred on the phylogenetic tree and in which of the two known domains. Overexpression lines and T-DNA insertion mutants of A. thaliana for AL7 gene found to be under positive selection on the PHD finger domain were tested for salt tolerance to understand the physiological effects of the evolutionarily significant gene.
The study found that positive selection operated on four branches and there were significant differences in biased codon usage in the AL family between T. halophila and A. lyrata or A. thaliana. Distinctively, only the AL7 branch was under positive selection on the PHD-finger domain and the three members on the branch showed the smallest difference when codon bias was evaluated among the seven clusters. Functional analysis based on transgenic overexpression lines and T-DNA insertion mutants indicated that salt-stress-induced AtAL7 could play a negative role in salt tolerance of A. thaliana, suggesting that adaptive evolution occurred in the members of AL gene family.
The study entitled “Molecular Evolutionary Analysis of the Alfin-Like Protein Family in Arabidopsis lyrata, Arabidopsis thaliana, and Thellungiella halophila” has been published in PLoS ONE 8(7): e66838.