The faster evolution of signal peptide genes of Frankia in surfactome may be attributed to their cardinal role in symbiotic association.

The analysis of transmembrane proteins in Frankia genomes provided insight into the host-microbe interaction strategy of this nitrogen-fixing Actinobacteria. The transmembrane proteins (TM) with their extracellular part exposed on the surface of the cell and the peripheral membrane proteins play a crucial role in the interaction of Frankia with the infected host plant and are termed as 'surfactome' for this study. Our analysis identified two categories of transmembrane proteins: signaling-TM (STM) and non-signaling TM (NSTM) proteins. The STM category was further subdivided into Lipo, Sec, and TAT. The codon and amino acid usage analysis revealed the importance of compositional constraints, translational efficiency, tRNA adaptation index, and RSCU over Frankia. The COG analysis proved the role of surfactome in signal transduction. It was evident that STMs were evolving faster than NSTMs. Moreover, the signal part of the STM proteins was found to be more evolved than the mature part. This rapid evolution enables the signaling proteins to interact with diverse external stimuli more effectively, which may be essential for the host-microbe association between Frankia and Actinorhizal plants. In conclusion, the comprehensive analysis of surfactome among Frankia genomes provided valuable perceptions into the host-microbe interaction strategy of this nitrogen-fixing actinobacteria. The results suggest that the composition and evolution of these proteins are essential for successful host-microbe associations. Considering the uniqueness of these proteins we coined the term "surfactome" for them and called for further research on the mechanisms of plant–microbe interactions. [ABSTRACT FROM AUTHOR]