Duplication and evolution of devA-like genes in Streptomyces has resulted in distinct developmental roles

Understanding morphological transformations is essential to elucidating the evolution and developmental biology of many organisms. The Gram-positive soil bacterium, Streptomyces coelicolor has a complex lifecycle which lends itself well to such studies. We recently identified a transcriptional regulator, devA, which is required for correct sporulation in this organism, with mutants forming short, mis-septate aerial hyphae. devA is highly conserved within the Streptomyces genus along with a duplicate copy, devE. Disruption of devE indicates this gene also plays a role in sporulation; however the phenotype of a devE mutant differs from a devA mutant, forming long un-septate aerial hyphae. Transcriptional analysis of devA and devE indicates that they are expressed at different stages of the lifecycle. This suggests that following duplication they have diverged in regulation and function. Analysis of fully sequenced actinomycete genomes shows that devA is found in a single copy in morphologically simpler actinobacteria, suggesting that duplication has lead to increased morphological complexity. Complementation studies with devA from Salinispora, which sporulates but does not form aerial hyphae, indicates the ancestral gene cannot complement devA or devE, suggesting neo-functionalisation has occurred. Analysis of the synonymous and non-synonymous nucleotide changes within the devA paralogues suggest subfunctionalisation has occurred as both copies have diverged from the ancestral sequences. Divergence is also asymmetric with a higher level of functional constraint observed in the DNA binding domain compared with the effector binding/oligomerisation domain, suggesting diversification in the substrate specificity of these paralogues has contributed to their evolution.