Transcriptomic analyses in the gametophyte ofDryopteris affinis: apomixis and more

The gametophyte of the fern Dryopteris affinis ssp. affinis represents a good model to explore the molecular basis of vegetative and reproductive development, as well as stress responses. Specifically, this fern reproduces asexually by apogamy, a peculiar case of apomixis whereby a sporophyte forms directly from a gametophytic cell without fertilization. Using an RNA-sequencing approach, we have previously annotated more than six thousand transcripts. Here, we selected one hundred of the inferred proteins that seemed particularly interesting for a detailed study of their potential functions, protein-protein interactions, and molecular phylogenies. As expected, a plethora of proteins associated with gametogenesis and embryogenesis in angiosperms, such as FERONIA (FER) and CHROMATING REMODELING 11 (CHR11) were identified, and more than a dozen candidates potentially involved in apomixis, such as ARGONAUTE4 (AGO4), AGO9, and AGO10, BABY BOOM (BBM), FASCIATED STEM4 (FAS4), FERTILIZATION-INDEPENDENT ENDOSPERM (FIE), and MATERNAL EFFECT EMBRYO ARREST29 (MEE29). In addition, proteins involved in the response to biotic and abiotic stresses were widely represented, as shown by the enrichment of heat-shock proteins. Using the String platform, studying interactomes revealed that most of the protein-protein interactions were predicted based on experimental, database, and text mining datasets, with MULTICOPY SUPPRESSOR OF IRA4 (MSI4) showing the highest number of 16 interactions. Lastly, some proteins were studied from a phylogenetic point of view, comparing the alignments with respect to more distantly or closely related plant groups, identifying AGO1 as the evolutionarily most similar to that other ferns and the most distant to the predicted common ancestor. This work sets the stage for future functional characterizations in relation to gametophyte development including apomictic reproduction.