The Unique Role of the ECERIFERUM2-LIKE Clade of the BAHD Acyltransferase Superfamily in Cuticular Wax Metabolism

The elongation of very-long-chain fatty acids is a conserved process used for the production of many metabolites, including plant cuticular waxes. The elongation of precursors of the most abundant cuticular wax components of some plants, however, is unique in requiring ECERIFERUM2-LIKE (CER2-LIKE) proteins. CER2-LIKEs are a clade within the BAHD superfamily of acyltransferases. They are known to be required for cuticular wax production in both Arabidopsis and maize based on mutant studies. Heterologous expression of Arabidopsis and rice CER2-LIKEs in Saccharomyces cerevisiae has demonstrated that they modify the chain-length specificity of elongation when paired with particular condensing enzymes. Despite sequence homology, CER2-LIKEs are distinct from the BAHD superfamily in that they do not appear to use acyl transfer activity to fulfill their biological function. Here, we review the discovery and characterization of CER2-LIKEs, propose several models to explain their function, and explore the importance of CER2-LIKE proteins for the evolution of plant cuticles.Science, Faculty ofBotany, Department ofReviewedFacult

Evolution of Geosiris (Iridaceae): historical biogeography and plastid-genome evolution in a genus of non-photosynthetic tropical rainforest herbs disjunct across the Indian Ocean

Mycoheterotrophs, i.e. plants that acquire carbon from root-associated soil fungi, often have highly degraded plastomes, reflecting relaxed selective constraints on plastid genes following the loss of photosynthesis. Geosiris Baill. is the only mycoheterotrophic genus in Iridaceae and comprises two species in Madagascar and nearby islands, and a third recently discovered species in north-eastern Australia. Here, we characterise the plastomes of the Australian and one Madagascan species to compare patterns of plastome degradation in relation to autotrophic and other mycoheterotrophic taxa and investigate the evolutionary and biogeographical history of the genus in Iridaceae. Both examined species have lost approximately half their plastid-encoded genes and a small but significant reduction in purifying selection in retained non-photosynthetic genes was observed. Geosiris is confirmed as monophyletic, with initial divergence of the genus occurring c. 53 million years ago, and subsequent diversification occurring c. 30 million years ago. Africa (including Madagascar) is reconstructed as the most likely ancestral area of the genus, implying a major range-expansion event of one lineage to Australia after its divergence in the Oligocene. Our study has highlighted the dynamic evolutionary history of Geosiris, contributed to the characterisation of mycoheterotrophic plastomes, and furthered our understanding of plastome structure and function

Organellomic data sets confirm a cryptic consensus on (unrooted) land‐plant relationships and provide new insights into bryophyte molecular evolution

Premise Phylogenetic trees of bryophytes provide important evolutionary context for land plants. However, published inferences of overall embryophyte relationships vary considerably. We performed phylogenomic analyses of bryophytes and relatives using both mitochondrial and plastid gene sets, and investigated bryophyte plastome evolution. Methods We employed diverse likelihood‐based analyses to infer large‐scale bryophyte phylogeny for mitochondrial and plastid data sets. We tested for changes in purifying selection in plastid genes of a mycoheterotrophic liverwort (Aneura mirabilis) and a putatively mycoheterotrophic moss (Buxbaumia), and compared 15 bryophyte plastomes for major structural rearrangements. Results Overall land‐plant relationships conflict across analyses, generally weakly. However, an underlying (unrooted) four‐taxon tree is consistent across most analyses and published studies. Despite gene coverage patchiness, relationships within mosses, liverworts, and hornworts are largely congruent with previous studies, with plastid results generally better supported. Exclusion of RNA edit sites restores cases of unexpected non‐monophyly to monophyly for Takakia and two hornwort genera. Relaxed purifying selection affects multiple plastid genes in mycoheterotrophic Aneura but not Buxbaumia. Plastid genome structure is nearly invariant across bryophytes, but the tufA locus, presumed lost in embryophytes, is unexpectedly retained in several mosses. Conclusions A common unrooted tree underlies embryophyte phylogeny, [(liverworts, mosses), (hornworts, vascular plants)]; rooting inconsistency across studies likely reflects substantial distance to algal outgroups. Analyses combining genomic and transcriptomic data may be misled locally for heavily RNA‐edited taxa. The Buxbaumia plastome lacks hallmarks of relaxed selection found in mycoheterotrophic Aneura. Autotrophic bryophyte plastomes, including Buxbaumia, hardly vary in overall structure