In silico analysis of the LRR receptor-like serine threonine kinases subfamily in Morus notabilis

Mulberries are important trees crops for orchards and agroforestry systems, which are plagued by many phytopathogenic fungal species. Leucine rich repeats (LRRs) receptor-like serine threonine kinases (LRR-RSTK) subfamily plays an important role in plant defense-related reactions against fungal attacks. In the present study, we mined this subfamily on Morus notabilis, a mulberry species whose relevant annotated genome assembly has recently become publicly available. Our aim was to decipher in silico the expansion and phylogeny of these genes, their homology relationships against their orthologous in woody angiosperm plant species, and the existence of positive selective pressures acting upon their LRRs. This subfamily was found to be quite abundant and diverged, comprising by 142 annotated gene members and containing a range of conserved functional domains in their C-termini, whilst their LRRs number ranged from one to 17 repeats. A phylogenetic investigation revealed 12 distinct clades based on their diverse structural profiles, mainly as a result of the fused functional domains at their C-termini. The interspecific expansion of these M. notabilis LRR-RSTKs has been investigated by a homology analysis across 12 other woody angiosperm species, showing that the highest proportion of homologous best BLAST hits observed primarily in Prunus persica, Malus domestica and Theobroma cacao. Using a series of maximum likelihood analyses, extensive episodes of positive selective pressures acting across the LRRs were observed. This overall evidence supports a potential crucial role of this diverged LRR-RSTK subfamily as a surveillance mechanism of M. notabilis against fungal attacks by providing rapidly evolving ligand-binding specificities.