Apomixis: oh, what a tangled web we have!

Abstract

Main conclusion Apomixis is a complex evolutionary trait with many possible origins. Here we discuss various clues and causes, ultimately proposing a model harmonizing the three working hypotheses on the topic. Abstract Asexual reproduction through seeds, i.e., apomixis, is the holy grail of plant biology. Its implementation in modern breeding could be a game-changer for agriculture. It has the potential to generate clonal crops and maintain valuable complex genotypes and their associated heterotic traits without inbreeding depression. The genetic basis and origins of apomixis are still unclear. There are three central hypothesis for the development of apomixis that could be: i) a deviation from the sexual developmental program caused by an asynchronous development, ii) environmentally triggered through epigenetic regulations (a polyphenism of sex), iii) relying on one or more genes/alleles. Because of the ever-increasing complexity of the topic, the path toward a detailed understanding of the mechanisms underlying apomixis remains unclear. Here, we discuss the most recent advances in the evolution perspective of this multifaceted trait. We incorporated our understanding of the effect of endogenous effectors, such as small RNAs, epigenetic regulation, hormonal pathways, protein turnover, and cell wall modification in response to an upside stress. This can be either endogenous (hybridization or polyploidization) or exogenous environmental stress, mainly due to oxidative stress and the corresponding ROS (Reacting Oxygen Species) effectors. Finally, we graphically represented this tangled web.

Gymnadenia winkeliana—A New Orchid Species to Romanian Flora

“…In sporophytic apomixis, also known as adventitious embryony, embryos develop directly from the somatic tissues of the ovules, located outside the embryo sac, i.e., from either the nucellar (nucellar embryony) or the integumental cells (integumentary embryony) of the ovule [53,55,58,59]. Additionally, in sporophytic apomixis, the formation of the embryo sac was reported to proceed normally, with the megaspore mother cell (MMC) undergoing multiple meiotic and mitotic cycles, resulting in the development of a sevencelled, eight-nucleate/octanucleate embryo sac [47,60,61]. As a result, embryo sac formation is not directly associated with apomixis, leading to the production of a functional haploid egg cell [58,62].…”

Expression Profiling of MSP1 Gene Involved in Mega-gametophyte Development in Ploidy Series of Guinea Grass (Panicum maximum Jacq.)

“…If the mother plant is well-adapted to a specific environment or purpose, the offspring will inherit those beneficial traits. Consequently, apomixis is highly desirable in agriculture due to its ability to maintain hybrid vigor [6]. Apomixis has several benefits as it allows for one-time hybrid creation, enabling seed propagation across multiple generations, cutting hybrid seed production costs and empowering farmers to produce their own hybrid seeds.…”

rDNA-FISH pattern in selected <i>Hieracium</i> species representing different ploidy levels

“…While some studies point to its relatively simple pattern of inheritance, obligatory apomixis is almost certainly a complex phenomenon influenced by unlinked gene loci (Hojsgaard, 2020;Niccolo et al, 2023). According to Carman's (1997) duplicate-gene asynchrony hypothesis, the main cause of embryological anomalies associated with this type of reproduction is the hybridization-derived floral asynchrony triggered by the mismatch of parental sets of developmental genes.…”