In silico study of wall-associated kinase family reveals large-scale genomic expansion potentially connected with functional diversification in Populus

MECA; The wall-associated kinases (WAKs) are a family of transmembrane proteins involved in pathogen responses and cell elongation in Arabidopsis. They belong to the major receptor-like kinase (RLK) family in plants. Given their architecture and connection to the cell wall, WAKs are thought to perceive and propagate extracellular signals. This study reports the characterization of the WAK family in a woody species based on the v3.0 genome assembly of Populus trichocarpa. In silico analysis revealed a total of 175 PtWAK sequences classified into four groups based on protein domains. Of the PtWAKs, 91.5 % were found in tandem-duplicated clusters contributing to the expansion of the family in poplar. Microarray and EST expression data mining revealed contrasting temporal and spatial expression patterns in stress treatments for several WAK members. The WAKs in poplar form the largest WAK family encountered to date in plants. The combination of phylogenetic and transcriptional data showed that members in nonexpanded clusters were mainly expressed in developmental processes, whereas PtWAKs that had evolved independently in a species-specific way were structured in clusters and were involved in resistance responses. This paper offers an overview of WAK family structure in P. trichocarpa, which will be useful for further functional analysis of the PtWAK family.