Polyspermy in angiosperms: Its contribution to polyploid formation and speciation

Abstract

Polyploidization has played a major role in the long‐term diversification and evolutionary success of angiosperms. Triploid formation among diploid plants, which is generally considered to be achieved by fertilization of an unreduced gamete with a reduced one, has been accepted as a means of polyploid production. In addition, it has been supposed that polyspermy also contributes to the triploid formation in maize, wheat, and some orchids; however, such a mechanism has been considered uncommon because reproducing the polyspermic situation and unambiguously investigating developmental profiles of polyspermic zygotes are difficult. To overcome these problems, rice polyspermic zygotes have been successfully produced by electrofusion of an egg cell with two sperm cells, and their developmental profiles have been monitored. The triploid zygotes progress through karyogamy and divide into two‐celled embryos via a typical bipolar mitotic division; the two‐celled embryos further develop into triploid plants, indicating that polyspermic plant zygotes, unlike those of animals, can develop normally. Furthermore, progenies consisting of triparental genetic materials have been successfully obtained in Arabidopsis through the pollination of two different kinds of male parents with a female parent. These different pieces of evidence for development and emergence of polyspermic zygotes in vitro and in planta suggest that polyspermy is a key event in polyploidization and species diversification.

Genome evolution during bread wheat formation unveiled by the distribution dynamics of SSR sequences on chromosomes using FISH

“…Upon merging two or more different genomes into one nucleus, the nascent polyploid faces several challenges such as rescheduling chromosome pairing, gene expression and DNA replication, and reducing the cost of large genomes. To meet these challenges, the polyploid genome must undergo a series of genetic and epigenetic changes [2][3][4][5][6][7]. The epigenetic changes are mainly associated with methylation changes, while the genetic changes mainly involve a large number of sequence removal, genome rearrangements, rewiring of gene expression, and chromosome instability [4,[7][8][9].…”

Postzygotic reproductive isolation established in the endosperm: mechanisms, drivers and relevance

“…Furthermore, in addition to the increased incidence of unreduced gamete formation under cold conditions [124,128], lower temperatures were also shown to alleviate postzygotic endosperm barriers [135], suggesting that specific climatic conditions promote the formation of polyploids via triploid intermediates. Another mechanism that has been proposed to give rise to polyploids is polyspermy, whereby two sperm cells fertilize the egg and thus bypass the triploid block [136][137][138][139] (figure 3). Nevertheless, the reported frequency of polyspermy-induced triploids in Arabidopsis is about 100-fold lower than the frequency of unreduced male gamete formation reported in Brassicaceae [136,140].…”

Effect of Paternal Genome Excess on the Developmental and Gene Expression Profiles of Polyspermic Zygotes in Rice

“…In a recent study, the effects of parental genome imbalance on zygotic development were clarified by producing polyploid zygotes with an imbalanced parental genome ratio via the in vitro fertilization of isolated rice gametes and by elucidating the developmental profiles of the polyploid zygotes [10,11]. The results indicated that approximately 50%-75% of the polyploid zygotes with an excess of paternal genome content exhibited the developmental arrest, whereas most of the polyploid zygotes with an excess of maternal gamete/genome content developed normally, as diploid zygotes [10].…”