The Glycosyltransferase Repertoire of the Spikemoss Selaginella moellendorffii and a Comparative Study of Its Cell Wall

Abstract

Spike mosses are among the most basal vascular plants, and one species, Selaginella moellendorffii, was recently selected for full genome sequencing by the Joint Genome Institute (JGI). Glycosyltransferases (GTs) are involved in many aspects of a plant life, including cell wall biosynthesis, protein glycosylation, primary and secondary metabolism. Here, we present a comparative study of the S. moellendorffii genome across 92 GT families and an additional family (DUF266) likely to include GTs. The study encompasses the moss Physcomitrella patens, a non-vascular land plant, while rice and Arabidopsis represent commelinid and non-commelinid seed plants. Analysis of the subset of GT-families particularly relevant to cell wall polysaccharide biosynthesis was complemented by a detailed analysis of S. moellendorffii cell walls. The S. moellendorffii cell wall contains many of the same components as seed plant cell walls, but appears to differ somewhat in its detailed architecture. The S. moellendorffii genome encodes fewer GTs (287 GTs including DUF266s) than the reference genomes. In a few families, notably GT51 and GT78, S. moellendorffii GTs have no higher plant orthologs, but in most families S. moellendorffii GTs have clear orthologies with Arabidopsis and rice. A gene naming convention of GTs is proposed which takes orthologies and GT-family membership into account. The evolutionary significance of apparently modern and ancient traits in S. moellendorffii is discussed, as is its use as a reference organism for functional annotation of GTs.

Why Plants Were Terrestrial from the Beginning

“…Structural similarity does not yield unambiguous evidence for evolutionary orthology due to possible convergent evolution. A prime example is the occurrence of mixed-linkage glucans in both lycophytes and Poaceae not paralleled by orthologous biosynthetic genes [10]. Comparative genomics of 'primitive' and higher plants established genetic orthology between all the major polysaccharides in embryophytes [10].…”

“…A prime example is the occurrence of mixed-linkage glucans in both lycophytes and Poaceae not paralleled by orthologous biosynthetic genes [10]. Comparative genomics of 'primitive' and higher plants established genetic orthology between all the major polysaccharides in embryophytes [10]. Using transcriptomes instead of genomes, orthology was also established between land plants and charophytes [11].…”

A family of ROP proteins that suppress actin dynamics and are essential for polarized growth and cell adhesion

“…Curiously, the pectin polymer that bears Ca 2+ cross-bridges, homo-galacturonan, is recalcitrant to extraction through Ca 2+ chelation in the gametophores of P. patens (Domozych et al, 2014) and of Selaginella moellendorffii (Harholt et al, 2012) but apparently not in P. Patens protonemata (Moller et al, 2007). When stained with fluorophores specific for cellulose, the intensity in ROP RNAi cell walls was low compared with that of control or MyoXI RNAi plants, suggesting that cellulose is present in reduced amounts in the absence of ROP proteins.…”

Evolution of the cell wall components during terrestrialization

“…During evolution, CesA genes encoding the catalytic subunits of TCs were subjected to specialization [26], which in seed plants had occurred at least at two levels: first -specialization of entire complexes to cellulose biosynthesis for primary and secondary walls; second -diversification of CesA catalytic subunits within a single rosette and formation of hetero-oligomeric complexes [34]. The sequence of specialization events is a crucial aspect necessary for understanding the evolution of cellulose biosynthesis.…”

“…Therefore, functional specialization of entire terminal complexes occurred after the formation of rosettes [31]. Complexes specialized to produce primary and secondary walls evolved to hetero-oligomeric TCs due to the diversification of CesAs [31,34,[36][37][38][39]. This second specialization event took place probably after the divergence of lycophytes, in a common ancestor of ferns and seed plants.…”