Fay-Wei Li , 1 , 2 , Paul Brouwer 3 , Lorenzo Carretero-Paulet 4 , 5 , Shifeng Cheng 6 , Jan de Vries 7 , Pierre-Marc Delaux 8 , Ariana Eily 9 , Nils Koppers 10 , Li-Yaung Kuo 1 , Zheng Li 11 , Mathew Simenc 12 , Ian Small 13 , Eric Wafula 14 , Stephany Angarita 12 , Michael S. Barker 11 , Andrea Bräutigam 15 , Claude dePamphilis 14 , Sven Gould 16 , Prashant S. Hosmani 1 , Yao-Moan Huang 17 , Bruno Huettel 18 , Yoichiro Kato 19 , Xin Liu 6 , Steven Maere 4 , 5 , Rose McDowell 13 , Lukas A. Mueller 1 , Klaas G. J. Nierop 20 , Stefan A. Rensing 21 , Tanner Robison 22 , Carl J. Rothfels 23 , Erin M. Sigel 24 , Yue Song 6 , Prakash R. Timilsena 14 , Yves Van de Peer 4 , 5 , 25 , Hongli Wang 6 , Per K. I. Wilhelmsson 21 , Paul G. Wolf 22 , Xun Xu 6 , Joshua P. Der 12 , Henriette Schluepmann 3 , Gane K.-S. Wong 6 , 26 , Kathleen M. Pryer 9
2 July 2018
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 fern-specific 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 N 2-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.
The genomes of two fern species, Azolla filiculoides and Salvinia cucullata, are reported and provide insights into fern-specific whole-genome duplications, fern-specific insect-resistant gene evolution and fern–cyanobacterial symbiosis.