Characterisation of the legume SERK-NIK gene superfamily including splice variants: Implications for development and defence

To aid the understanding of signalling pathways in M. truncatula, we have identified and annotated the SERK genes in this species. Using degenerate PCR and database mining, eight more SERK-like genes have been identified and these have been shown to be expressed. The amplification and sequencing of several different PCR products from one of these genes is consistent with the presence of splice variants. Four of the eight additional genes identified are upregulated in cultured leaf tissue grown on embryogenic medium. The sequence information obtained from M. truncatula was used to identify SERK family genes in the recently sequenced soybean (Glycine max) genome.A total of nine SERK or SERK-like genes have been identified in M. truncatula and potentially 17 in soybean. Five M. truncatula SERK genes arose from duplication events not evident in soybean and Lotus. The presence of splice variants has not been previously reported in a SERK gene. Upregulation of four newly identified SERK genes (in addition to the previously described MtSERK1) in embryogenic tissue cultures suggests these genes also play a role in the process of somatic embryogenesis. The phylogenetic relationship of members of the SERK gene family to closely related genes, and to development and defence function is discussed.The plant receptor-like kinases (RLKs) are a large group of signalling proteins in plants, and are a fundamental part of plant signal transduction. In Arabidopsis the RLK family contains more than 600 members, constituting 60% of kinases, including almost all of the transmembrane kinases [1]. The position of RLKs in the plasma membrane, with an extracellular receptor domain and an intracellular kinase domain, makes them well suited to the task of perceiving a signal external to the cell and conducting that signal into the cell in order to elicit a response. In addition to RLKs there are a number of receptor-like proteins (RLPs). These proteins contain an extracellular domain similar to