Comprehensive analysis of proteins associated with light responses and stress tolerance in the gametophyte of the fern Dryopteris affinis ssp. affinis

The fern gametophyte, despite its crucial role as the pioneer stage ensuring the successful establishment of the fern, has remained largely neglected as a subject of research, being particularly evident at the molecular level. In this study, based on an RNA-sequenced gametophyte transcriptome from the apogamous fern Dryopteris affinis ssp. affinis, 1,160 proteins functionally associated with light responses, transport processes, and stress mechanisms were identified. Light-responsive proteins are linked to photosynthesis, photorespiration, xanthophyll metabolism, and photomorphogenesis. Among them are several HIGH CHLOROPHYLL FLUORESCENCE (HCF 136, 173 and 244), which participate in the formation of photosystem II, and ENHANCER OF VARIEGATION 3 (EVR3), which is involved in chloroplast biogenesis. Regarding photomorphogenesis, the protein list includes the photoreceptors PHYTOCHROME B (PHYB), CRYPTOCHROMES 1 and 2 (CRY1 and 2), PHOTOTROPIN 2 (PHOT2), and UV RESISTANCE LOCUS 2, 3 and 8 (UVR2, 3 and 8). Likewise, related to transport, 659 proteins were found either in membranes and cytoplasm, moving a wide range of molecules, such as PERMEASE 2 and 3 (AAP2 and 3), SUCROSE TRANSPORTER 4 (SUC4), AMMONIUM TRANSPORTER 1 (AMT1), MECHANOSENSITIVE ION CHANNEL PROTEIN 1 (MSL1), among others. Furthermore, our results comprised an extensive arsenal of proteins to battle against both biotic and abiotic stress, or involved in plant immunity, such as BRASSINOSTEROID-SIGNALLING KINASE 1 (BSK1), NON-RESPONDING TO OXYLIPINS 7 (NOXY7), and CALLOSE SYNTHASE 12 (CALS12); whereas -MANNOSIDASE 2 (GMII), PALMITOYL-MONOGALACTOSYLDIACYLGLYCEROL {Delta}-7 DESATURASE (ADS3), and FORGETTER 1 (FGT1) are linked to salt, cold or heat stresses, respectively. Analysis of protein-protein interactions revealed MODIFIED TRANSPORT TO THE VACUOLE 17 (MTV17) as the most connected protein, with 19 interactions, mainly supported by text-mining and database evidence. These findings contribute to expanding the limited knowledge at the molecular level of ferns overall, paving the way for future experimental investigations.