Evolutionary genomics of plant genes encoding N-terminal-TM-C2 domain proteins and the similar FAM62 genes and synaptotagmin genes of metazoans.

Background: Synaptotagmin genes are found in animal genomes and are known to function in the nervous system. Genes with a similar domain architecture as well as sequence similarity to synaptotagmin C2 domains have also been found in plant genomes. The plant genes share an additional region of sequence similarity with a group of animal genes named FAM62. FAM62 genes also have a similar domain architecture. Little is known about the functions of the plant genes and animal FAM62 genes. Indeed, many members of the large and diverse Syt gene family await functional characterization. Understanding the evolutionary relationships among these genes will help to realize the full implications of functional studies and lead to improved genome annotation.

Results: I collected and compared plant Syt-like sequences from the primary nucleotide sequence databases at NCBI. The collection comprises six groups of plant genes conserved in embryophytes: NTMC2Type1 to NTMC2Type6. I collected and compared metazoan FAM62 sequences and identified some similar sequences from other eukaryotic lineages. I found evidence of RNA editing and alternative splicing. I compared the intron patterns of Syt genes. I also compared Rabphilin and Doc2 genes.

Conclusion: Genes encoding proteins with N-terminal-transmembrane-C2 domain architectures resembling synaptotagmins, are widespread in eukaryotes. A collection of these genes is presented here. The collection provides a resource for studies of intron evolution. I have classified the collection into homologous gene families according to distinctive patterns of sequence conservation and intron position. The evolutionary histories of these gene families are traceable through the appearance of family members in different eukaryotic lineages. Assuming an intron-rich eukaryotic ancestor, the conserved intron patterns distinctive of individual gene families, indicate independent origins of Syt, FAM62 and NTMC2 genes. Resemblances among these large, multi-domain proteins are due not only to shared ancestry (homology) but also to convergent evolution (analogy). During the evolution of these gene families, duplications and other gene rearrangements affecting domain composition, have occurred along with sequence divergence, leading to complex family relationships with accordingly complex functional implications. The functional homologies and analogies among these genes remain to be established empirically.