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Emergence of apospory and bypass of meiosis via apomixis after sexual hybridisation and polyploidisation.

ABSTRACT: Hybridisation and polyploidy are major forces contributing to plant speciation. Homoploid (2x) and heteroploid (3x) hybrids, however, represent critical stages for evolution due to disturbed meiosis and reduced fertility. Apomixis--asexual reproduction via seeds--can overcome hybrid sterility, but requires several concerted alterations of developmental pathways to result in functional seed formation. Here, we analyse the reproductive behaviours of homo- and heteroploid synthetic hybrids from crosses between sexual diploid and tetraploid Ranunculus auricomus species to test the hypothesis that developmental asynchrony in hybrids triggers the shift to apomictic reproduction. Evaluation of male and female gametophyte development, viability and functionality of gametes shows developmental asynchrony, whereas seed set and germinability indicate reduced fitness in synthetic hybrids compared to sexual parents. We present the first experimental evidence for spontaneous apospory in most hybrids as an alternative pathway to meiosis, and the appearance of functional apomictic seeds in triploids. Bypassing meiosis permits these triploid genotypes to form viable seed and new polyploid progeny. Asynchronous development causes reduced sexual seed set and emergence of apospory in synthetic Ranunculus hybrids. Apomixis is functional in triploids and associated with drastic meiotic abnormalities. Selection acts to stabilise developmental patterns and to tolerate endosperm dosage balance shifts which facilitates successful seed set and establishment of apomictic lineages.

SUBMITTER: Hojsgaard D

PROVIDER: S-EPMC4260133 | biostudies-literature | 2014 Dec

REPOSITORIES: biostudies-literature

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Emergence of apospory and bypass of meiosis via apomixis after sexual hybridisation and polyploidisation.

Hojsgaard Diego D Greilhuber Johann J Pellino Marco M Paun Ovidiu O Sharbel Timothy F TF Hörandl Elvira E

The New phytologist 20140731 4

Hybridisation and polyploidy are major forces contributing to plant speciation. Homoploid (2x) and heteroploid (3x) hybrids, however, represent critical stages for evolution due to disturbed meiosis and reduced fertility. Apomixis--asexual reproduction via seeds--can overcome hybrid sterility, but requires several concerted alterations of developmental pathways to result in functional seed formation. Here, we analyse the reproductive behaviours of homo- and heteroploid synthetic hybrids from cro ...[more]

PMID: 25081588

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Project description:Apomixis (asexual seed formation) in angiosperms occurs either sporophytically, through adventitious embryony, or gametophytically, where an unreduced female gametophyte (embryo sac) forms and produces an unreduced egg that develops into an embryo parthenogenetically. Multiple types of gametophytic apomixis occur, and these are differentiated based on where and when the unreduced gametophyte forms, a process referred to as apomeiosis. Apomeiotic gametophytes form directly from ameiotic megasporocytes, as in Antennaria-type diplospory, from unreduced spores derived from 1st division meiotic restitutions, as in Taraxacum-type diplospory, or from cells of the ovule wall, as in Hieracium-type apospory. Multiple types of apomeiosis occasionally occur in the same plant, which suggests that the different types occur in response to temporal and/or spatial shifts in termination of sexual processes and onset timing of apomeiosis processes. To better understand the origins and evolutionary implications of apomixis in Boechera (Brassicaceae), we determined apomeiosis type for 64 accessions representing 44 taxonomic units. Plants expressing apospory and diplospory were equally common, and these generally produced reduced and unreduced pollen, respectively. Apospory and diplospory occurred simultaneously in individual plants of seven taxa. In Boechera, apomixis perpetuates otherwise sterile or semisterile interspecific hybrids (allodiploids) through multiple generations. Accordingly, ample time, in these multigenerational clones, is available for rare meioses to produce haploid, intergenomically recombined male and female gametes. The fusion of such gametes could then produce segmentally autoploidized progeny. If sex re-emerges among such progeny, then new and genomically unique sexual species could evolve. Herein, we present evidence that such apomixis-facilitated speciation is occurring in Boechera, and we hypothesize that it might also be occurring in facultatively apomictic allodiploids of other angiospermous taxa.

Project description:This study aims to report the epidemiology of sexual violence (SV) perpetration for both female and male youth across a broad age spectrum. Additionally, the etiology of SV perpetration is examined by identifying prior exposures that predict a first SV perpetration. Six waves of data were collected nationally online, between 2006 and 2012, from 1586 youth between 10 and 21 years of age. Five types of SV were assessed: sexual harassment, sexual assault, coercive sex, attempted rape, and rape. To identify how prior exposures may predict the emergence of SV in adolescence, parsimonious lagged multivariable logistic regression models estimated the odds of first perpetrating each of the five types of SV within the context of other variables (e.g., rape attitudes). Average age at first perpetration was between 15 and 16 years of age, depending on SV type. Several characteristics were more commonly reported by perpetrators than non-perpetrators (e.g., alcohol use, other types of SV perpetration and victimization). After adjusting for potentially influential characteristics, prior exposure to parental spousal abuse and current exposure to violent pornography were each strongly associated with the emergence of SV perpetration-attempted rape being the exception for violent pornography. Current aggressive behavior was also significantly implicated in all types of first SV perpetration except rape. Previous victimization of sexual harassment and current victimization of psychological abuse in relationships were additionally predictive of one's first SV perpetration, albeit in various patterns. In this national longitudinal study of different types of SV perpetration among adolescent men and women, findings suggest several malleable factors that need to be targeted, especially scripts of inter-personal violence that are being modeled by abusive parents in youths' homes and also reinforced by violent pornography. The predictive value of victimization for a subsequent first SV perpetration highlights the inter-relatedness of different types of violence involvement. Universal and holistic prevention programming that targets aggressive behaviors and violent scripts in inter-personal relationships is needed well before the age of 15 years.

Dataset Information

Emergence of apospory and bypass of meiosis via apomixis after sexual hybridisation and polyploidisation.

Publications

Emergence of apospory and bypass of meiosis via apomixis after sexual hybridisation and polyploidisation.

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