Sexual and apogamous species of woodferns show different protein and phytohormone profiles

Abstract

The gametophyte of ferns reproduces either by sexual or asexual means. In the latter, apogamy represents a peculiar case of apomixis in which an embryo is formed from somatic cells. A proteomic and physiological approach was applied to the apogamous fern Dryopteris affinis ssp. affinis and its sexual relative D. oreades. The proteomic analysis compared apogamous versus female gametophytes, whereas the phytohormone study included, in addition to females, three apogamous stages (filamentous, spatulate and cordate). The proteomic profiles revealed a total of 879 proteins and, after annotation, differential regulation was found in 206 proteins of D. affinis and 166 of its sexual counterpart. The proteins upregulated in D. affinis are mostly associated with protein metabolism (including folding, transport and proteolysis), ribosome biogenesis, gene expression and translation, while in the sexual counterpart they are largely related to starch and sucrose metabolism, energy generation and photosynthesis. Ultra-performance liquid chromatography–tandem spectrometry (UHPLC–MS/MS) was used to assess the levels of indole-3-acetic acid (IAA); the cytokinins 6-benzylaminopurine (BA), trans-zeatine (Z), trans-zeatin riboside (ZR), dihydrozeatine (DHZ), dihydrozeatin riboside (DHZR), isopentenyl adenine (iP) and isopentenyl adenosine (iPR); abscisic acid (ABA); the gibberellins GA3 and GA4; salicylic acid (SA); and the brassinosteroids brassinolide (BL) and castasterone (CS). IAA, the cytokinins Z, ZR and iPR, the gibberellin GA4, castasterone and ABA accumulated more in the sexual gametophyte than in the apogamous one. When comparing the three apogamous stages, BA and SA peaked in the filamentous stage, GA3 and BL in the spatulate stage, and DHZR in the cordate gametophytes. The results point to the existence of marked metabolic differences between apogamous and sexual gametophytes and support the use of the fern gametophyte as a valuable experimental system to deepen our understanding of plant reproduction.