Duminil, P. | Search bioRxiv

bioRxiv2026

Glycosylceramide assembly and function in a model bryophyte

Research ConductedTo elucidate the functions of glycosylceramides, we generated and characterized mutants deficient in multiple steps contributing to their assembly in the model moss Physcomitrium patens. We mutagenized SPHINGOLIPID {Delta}8-DESATURASE, whose products are preferentially incorporated into glycosylceramides, and a suite of higher-order mutants combining sphingolipid {Delta}4-desaturase and glycosyl ceramide synthase. MethodsWe used targeted lipidomics to describe the chemotypes of all mutants. We used quantitative phenotype analysis, transcriptomics, and phytohormone profiling to understand the effects of these chemotypes on development and physiology. Key ResultsThese mutants present a range of phenotypes that collectively indicate that in P. patens (1) glycosylceramide deficiency impairs development, largely due to imbalance in free ceramide homeostasis (2) the synthesis of glycosylceramides is dependent upon the presence of a specific free ceramide profile (3) the {Delta}4-, but not the {Delta}8-desaturation, is strictly required for glycosylceramide synthesis, (4) cell division and differentiation, but not cell expansion, are affected by sphingolipid imbalance, and (5) sphingolipid imbalance results in oxylipin accumulation. ConclusionCollectively, our results elucidate the assembly and functions of glycosylceramides in a model bryophyte, and highlight conserved and specialized aspects of sphingolipid metabolism among plants.

plant biology↗

bioRxiv2025

Setaphyte VERY-LONG-CHAIN FATTY ACYL DESATURASES are desaturases that impact glycerolipid and sphingolipid metabolism

Desaturases in plants are diverse. They vary in localization, source of reducing power, and substrate preference, accepting glycerolipids, long-chain bases, acyl-CoAs, and acyl-ACPs, in varying states of (un)saturation and chain length. Their products are incorporated into membrane glycerolipids, sphingolipids, or storage lipids. We previously characterized a desaturase from Physcomitrium patens that predominantly affects the monounsaturation of very-long-chain fatty acyl (VLCFA) moieties of sphingolipids, naming this desaturase SPHINGOLIPID FATTY ACYL DESATURASE (SFD). Among embryophytes, candidate SFDs were only identified in setaphytes, including one paralog in P. patens and an ortholog in Marchantia polymorpha. Here, we characterize the P. patens paralog, and clarify via mutant analysis that SFDs affect not only sphingolipid metabolism, but also glycerolipid metabolism. We express both paralogs, as well as the candidate gene from M. polymorpha, in Saccharomyces cerevisiae, and show they desaturate VLCFAs incorporated into sphingolipids, triacylglycerols, and acyl-CoAs. The simplest explanation is that "SFDs" likely accept an acyl-CoA, rather than a sphingolipid substrate, as initially proposed. We suggest renaming these desaturases VERY-LONG-CHAIN FATTY ACYL DESATURASES (VFADs). The physiological functions of VFADs and analogous enzymes from other plant systems are discussed, as are the challenges with classifying desaturase activities. HighlightVFADs from P. patens and M. polymorpha produce monounsaturated very-long-chain fatty acids that are incorporated into sphingolipids and glycerolipids, likely via desaturation of an acyl-CoA substrate

plant biology↗