Control of the Azolla symbiosis sexual reproduction: ferns to shed light on the origin of floral regulation?

ABSTRACTAzolla ferns and the filamentous cyanobacteria Nostoc azollae constitute a model symbiosis that enabled colonization of the water surface with traits highly desirable for development of more sustainable crops: their floating mats capture CO2 and fixate N2 at high rates phototrophically. Their mode of sexual reproduction is heterosporous. Regulation of the transition from vegetative to spore-forming phases in ferns is largely unknown, yet a pre-requisite for Azolla domestication, and of particular interest since ferns represent the sister lineage of seed plants.Far-red light (FR) induced sporocarp formation in A. filiculoides. Sporocarps obtained, when crossed, verified species attribution of Netherlands strains but not Iran’s Anzali lagoon. FR-responsive transcripts included CMADS1 MIKCC-homologues and miRNA-controlled GAMYB transcription factors in the fern, transporters in N.azollae, and ycf2 in chloroplasts. Loci of conserved miRNA in the fern lineage included miR172, yet FR only induced miR529 and miR535, and reduced miR319 and miR159.Suppression of sexual reproduction in both gametophyte and sporophyte-dominated plant lineages by red light is likely a convergent ecological strategy in open fields as the active control networks in the different lineages differ. MIKCC transcription factor control of flowering and flower organ specification, however, likely originated from the diploid to haploid phase transition in the homosporous common ancestor of ferns and seed plants.

Light and temperature induced sporocarp formation of Phellinusweirii

Eight isolates of Phellinusweirii (Murr.) Gilb. (Poriaweirii (Murr.) Murr.), a serious pathogen of conifer roots in northwestern United States and southern British Columbia, formed sporocarps on malt agar after exposure to continuous near-ultraviolet light for 4 days at certain temperatures followed by incubation at normal laboratory temperature (22–24 °C) and lighting conditions (118 lx for 8–9 h). Isolates G7312 and T-55 formed sporocarps when cultures were placed in normal or inverted positions; other isolates produced sporocarps only in an inverted position. Effective light–temperature combinations varied among isolates. Of all isolates, only G7312 and T-55 were induced to form sporocarps by fluorescent white light.