Did apomixis evolve from sex or was it the other way around?. (11th March 2019)

• Record Type: Journal Article
• Authors: Albertini, Emidio; Barcaccia, Gianni; Carman, John G; Pupilli, Fulvio
• Is Part Of: Journal of experimental botany. Volume 70:Number 11(2019)
• Page Start: 2951
• Page End: 2964
• Publication Date: 2019-03-11
• Subjects: Apomeiosis -- apomixis -- eukaryogenesis -- meiosis -- origins of sex -- parthenogenesis -- plant reproduction; Botany -- Periodicals; Botany, Experimental -- Periodicals; Plant physiology -- Periodicals; 580
• DOI: 10.1093/jxb/erz109
• Languages: English
• ISSNs: 0022-0957

Abstract

Abstract : This review considers the possibility that apomixis is a highly conserved but evolutionarily suppressed alternative to sex, that apomixis and sex are anciently polyphenic, and that the switch between them is controlled by upstream epigenetic processes that are environmentally triggered Abstract: In angiosperms, there are two pathways of reproduction through seeds: sexual, or amphimictic, and asexual, or apomictic. The essential feature of apomixis is that an embryo in an ovule is formed autonomously. It may form from a cell of the nucellus or integuments in an otherwise sexual ovule, a process referred to as adventitious embryony. Alternatively, the embryo may form by parthenogenesis from an unreduced egg that forms in an unreduced embryo sac. The latter may form from an ameiotic megasporocyte, in which case it is referred to as diplospory, or from a cell of the nucellus or integument, in which case it is referred to as apospory. Progeny of apomictic plants are generally identical to the mother plant. Apomixis has been seen over the years as either a gain- or loss-of-function over sexuality, implying that the latter is the default condition. Here, we consider an additional point of view, that apomixis may be anciently polyphenic with sex and that both reproductive phenisms involve anciently canalized components of complex molecular processes. This polyphenism viewpoint suggests that apomixis fails to occur in obligately sexual eukaryotes because genetic or epigenetic modifications have silenced the primitive sex apomixis switch and/or disrupted molecular capacities for apomixis. In eukaryotes where sex and apomixis are clearly polyphenic, apomixis exponentially drives clonal fecundity during reproductively favorable conditions, while stress induces sex for stress-tolerant spore or egg formation. The latter often guarantees species survival during environmentally harsh seasons.