Ferns are the closest sister group to all seed plants, yet little is known about their genomes other than that they are generally colossal. Here, we report on the genomes of Azolla filiculoides and Salvinia cucullata (Salviniales) and present evidence for episodic whole-genome duplication in ferns—one at the base of 'core leptosporangiates' and one specific to Azolla. One fernspecific gene that we identified, recently shown to confer high insect resistance, seems to have been derived from bacteria through horizontal gene transfer. Azolla coexists in a unique symbiosis with N2-fixing cyanobacteria, and we demonstrate a clear pattern of cospeciation between the two partners. Furthermore, the Azolla genome lacks genes that are common to arbuscular mycorrhizal and root nodule symbioses, and we identify several putative transporter genes specific to Azolla–cyanobacterial symbiosis. These genomic resources will help in exploring the biotechnological potential of Azolla and address fundamental questions in the evolution of plant life. ; Partly supported by the Shenzhen Municipal Government of China (no. JCYJ20150529150409546), the National Science Foundation Doctoral Dissertation Improvement Grant DEB-1407158 (to K.M.P. and F.-W.L.) and the German Research Foundation Research Fellowship VR132/1-1 (to J.d.V.). ; http://www.nature.com/nplants ; am2018 ; Biochemistry ; Genetics ; Microbiology and Plant Pathology
Green plants (Viridiplantae) include around 450,000-500,000 species(1,2) of great diversity and have important roles in terrestrial and aquatic ecosystems. Here, as part of the One Thousand Plant Transcriptomes Initiative, we sequenced the vegetative transcriptomes of 1,124 species that span the diversity of plants in a broad sense (Archaeplastida), including green plants (Viridiplantae), glaucophytes (Glaucophyta) and red algae (Rhodophyta). Our analysis provides a robust phylogenomic framework for examining the evolution of green plants. Most inferred species relationships are well supported across multiple species tree and supermatrix analyses, but discordance among plastid and nuclear gene trees at a few important nodes highlights the complexity of plant genome evolution, including polyploidy, periods of rapid speciation, and extinction. Incomplete sorting of ancestral variation, polyploidization and massive expansions of gene families punctuate the evolutionary history of green plants. Notably, we find that large expansions of gene families preceded the origins of green plants, land plants and vascular plants, whereas whole-genome duplications are inferred to have occurred repeatedly throughout the evolution of flowering plants and ferns. The increasing availability of high-quality plant genome sequences and advances in functional genomics are enabling research on genome evolution across the green tree of life. ; Alberta Ministry of Advanced Education; Alberta Innovates AITF/iCORE Strategic Chair [RES0010334]; Musea Ventures; National Key Research and Development Program of China [2016YFE0122000]; Ministry of Science and Technology of the People's Republic of ChinaMinistry of Science and Technology, China [2015BAD04B01/2015BAD04B03]; State Key Laboratory of Agricultural Genomics [2011DQ782025]; Guangdong Provincial Key Laboratory of core collection of crop genetic resources research and application [2011A091000047]; Shenzhen Municipal Government of China [CXZZ20140421112021913/JCYJ20150529150409546/JCYJ20150529150505656]; National Science FoundationNational Science Foundation (NSF) [DBI-1265383, IOS 0922742, IOS-1339156, DEB 0830009, EF-0629817, EF-1550838, DEB 0733029, DBI 1062335, 1461364]; National Institutes of HealthUnited States Department of Health & Human ServicesNational Institutes of Health (NIH) - USA [1R01DA025197]; Deutsche ForschungsgemeinschaftGerman Research Foundation (DFG) [Qu 141/5-1, Qu 141/6-1, GR 3526/7-1, GR 3526/8-1]; Natural Sciences and Engineering Research Council of CanadaNatural Sciences and Engineering Research Council of Canada ; The 1KP initiative was funded by the Alberta Ministry of Advanced Education and Alberta Innovates AITF/iCORE Strategic Chair (RES0010334) to G.K.-S.W., Musea Ventures, The National Key Research and Development Program of China (2016YFE0122000), The Ministry of Science and Technology of the People's Republic of China (2015BAD04B01/2015BAD04B03), the State Key Laboratory of Agricultural Genomics (2011DQ782025) and the Guangdong Provincial Key Laboratory of core collection of crop genetic resources research and application (2011A091000047). Sequencing activities at BGI were also supported by the Shenzhen Municipal Government of China (CXZZ20140421112021913/JCYJ20150529150409546/JCYJ20150529150505656). Computation support was provided by the China National GeneBank (CNGB), the Texas Advanced Computing Center (TACC), WestGrid and Compute Canada; considerable support, including personnel, computational resources and data hosting, was also provided by the iPlant Collaborative (CyVerse) funded by the National Science Foundation (DBI-1265383), National Science Foundation grants IOS 0922742 (to C.W.d., P.S.S., D.E.S. and J.H.L.-M.), IOS-1339156 (to M.S.B.), DEB 0830009 (to J.H.L.-M., C.W.d., S.W.G. and D.W.S.), EF-0629817 (to S.W.G. and D.W.S.), EF-1550838 (to M.S.B.), DEB 0733029 (to T.W. and J.H.L.-M.), and DBI 1062335 and 1461364 (to T.W.), a National Institutes of Health Grant 1R01DA025197 (to T.M.K., C.W.d. and J.H.L.-M.), Deutsche Forschungsgemeinschaft grants Qu 141/5-1, Qu 141/6-1, GR 3526/7-1, GR 3526/8-1 (to M.Q. and I.G.) and a Natural Sciences and Engineering Research Council of Canada Discovery grant (to S.W.G.). We thank all national, state, provincial and regional resource management authorities, including those of province Nord and province Sud of New Caledonia, for permitting collections of material for this research. ; Public domain authored by a U.S. government employee
