Azolla domestication towards a biobased economy?

Abstract

SummaryDue to its phenomenal growth requiring neither nitrogen fertilizer nor arable land and its biomass composition, the mosquito fern Azolla is a candidate crop to yield food, fuels and chemicals sustainably. To advance Azolla domestication, we research its dissemination, storage and transcriptome.Methods for dissemination, cross-fertilization and cryopreservation of the symbiosis Azolla filiculoides-Nostoc azollae are tested based on the fern spores. To study molecular processes in Azolla including spore induction, a database of 37 649 unigenes from RNAseq of microsporocarps, megasporocarps and sporophytes was assembled, then validated.Spores obtained year-round germinated in vitro within 26 d. In vitro fertilization rates reached 25%. Cryopreservation permitted storage for at least 7 months. The unigene database entirely covered central metabolism and to a large degree covered cellular processes and regulatory networks. Analysis of genes engaged in transition to sexual reproduction revealed a FLOWERING LOCUS T-like protein in ferns with special features induced in sporulating Azolla fronds.Although domestication of a fern-cyanobacteria symbiosis may seem a daunting task, we conclude that the time is ripe and that results generated will serve to more widely access biochemicals in fern biomass for a biobased economy.

Field Guide to Plant Model Systems

“…Ferns evolved leaves independently of seed plants, and whether the molecular mechanisms are similar is actively being investigated (Plackett et al, 2015). Ferns are often polyploids with large genomes, and while no draft fern genome sequences are currently available (Wolf et al, 2015), transcriptome assemblies of Azolla filiculoides (an aquatic fern; genome of 740 Mb) and Equisetum giganteum (horsetail) have provided some insight into gene content (Vanneste et al, 2015; Brouwer et al, 2014). A derived fern, Ceratopteris richardii (11.26 Gb) has been developed to some extent as a model system with genetic approaches; e.g., investigations of sex determination mechanisms (Strain et al, 2001; Atallah and Banks, 2015) and transformation protocols have been established (Muthukumar et al, 2013; Plackett et al, 2014).…”

Is there foul play in the leaf pocket? The metagenome of floating fern Azolla reveals endophytes that do not fix N2 but may denitrify

“…A single fern genus, Azolla , benefits from such a cyanobacterial symbiosis, and stands out for its prolific growth, resulting in high protein biomass without nitrogen fertilizer. For example, Azolla filiculoides produced 39 t ha −1 yr −1 dry weight (DW) biomass containing up to 25% protein (Becerra et al ., ; Brouwer et al ., ), whereas clover, Trifolium pratense , a high‐yielding forage legume that is commonly grown with low fertilizer applications (150 kg ha −1 yr −1 ), produced up to 15 t ha −1 yr −1 DW biomass containing similar protein amounts (Anglade et al ., ). The cyanobacterial symbiont Nostoc azollae is key to the fern's remarkable productivity.…”

Crowdfunding the Azolla fern genome project: a grassroots approach

“…First, Asian farmers have been using Azolla for thousands of years as a companion crop for rice—the world’s most important food staple [2]. Azolla is a natural nitrogen biofertilizer, a green manure, that bolsters rice productivity when these two plants are grown together [3,4]. Furthermore, Azolla has been shown to be capable of hyperaccumulating a great variety of heavy metal pollutants, as well as decontaminating superfluous ammonium and phosphorus in wastewater [5,6].…”