Insights into the evolution of multicellularity from the sea lettuce genome

We report here the 98.5 Mbp haploid genome (12,924 protein coding genes) of Ulva mutabilis, a ubiquitous and iconic representative of the Ulvophyceae or green seaweeds. Ulva’s rapid and abundant growth makes it a key contributor to coastal biogeochemical cycles; its role in marine sulfur cycles is particularly important because it produces high levels of dimethylsulfoniopropionate (DMSP), the main precursor of volatile dimethyl sulfide (DMS). Rapid growth makes Ulva attractive biomass feedstock but also increasingly a driver of nuisance “green tides.” Ulvophytes are key to understanding the evolution of multicellularity in the green lineage, and Ulva morphogenesis is dependent on bacterial signals, making it an important species with which to study cross-kingdom communication. Our sequenced genome informs these aspects of ulvophyte cell biology, physiology, and ecology. Gene family expansions associated with multicellularity are distinct from those of freshwater algae. Candidate genes, including some that arose following horizontal gene transfer from chromalveolates, are present for the transport and metabolism of DMSP. The Ulva genome offers, therefore, new opportunities to understand coastal and marine ecosystems and the fundamental evolution of the green lineage.Research support was provided by NERC grant NBAF925 and BBSRC grant BB:K020552 (to C.A.M. and J.H.B.), UGent Special Research FundBOF/01J04813 (to O.D.C. and K.V.), BOF/GOA 01G01715 (to K.V. and E.V), and BOF/01SC2316 (to X.L.) with infrastructure funded by EMBRC Belgium—FWO project GOH3817N (to O.D.C.), EU Horizon2020 Marie Curie ITN ALFF-Project642575 (to C.M.G., O.D.C., T.W., G.C., and Y.V.d.P.), German Research Foundation CRC ChemBioSys1127 (to T.W., J. Boesger, M.K., G.C., and L.L.), Postdoctoral Fellowship Grant of the Research Foundation—Flanders (to J. Blomme—project 12T3418N), BBSRC-funded MIBTP PhD rotation project (to R.C. and J.C.C.), United States Department of EnergyDE-EE0003373/001 (to D.B.), and National Science Foundation IGERT for Renewable and Sustainable Fuels program 0903675 (to F.F.). M.H. is research associate of the FNRS. We thank Dr. Severin Sasso (University Jena) for providing T.W. with the real-time PCR detection system. This publication is based upon work from COST Action FA1406 PHYCOMORPH (to B.C., J.C.C, J.H.B., O.D.C., S.A.R., and T.W.), supported by COST (European Cooperation in Science and Technology).https://www.journals.elsevier.com/current-biology2019-09-24hj2018Genetic