The Arabidopsis MutantjasonProduces Unreduced First Division Restitution Male Gametes through a Parallel/Fused Spindle Mechanism in Meiosis II    

Abstract

In plants, whole-genome doubling (polyploidization) is a widely occurring process largely contributing to plant evolution and diversification. The generation and fusion of diploid gametes is now considered the major route of plant polyploidization. The parallel arrangement or fusion of meiosis II MII spindles (ps) is one of the most frequently reported mechanisms generating triploid offspring. Through a forward genetics screen of an Arabidopsis (Arabidopsis thaliana) ethyl methanesulfonate population, we identified Arabidopsis thaliana Parallel Spindles1 (AtPS1), which was recently reported as a major gene implicated in the control of the ps meiotic defect. In addition, we describe the isolation and characterization of a novel allele of JASON, involved in male gametophytic ploidy regulation in plants. Similar to atps1 mutants, jason produces more than 25% 2n pollen grains and spontaneously forms triploid offspring. By combining both cytological and genetic approaches, we demonstrate that loss of JASON causes the formation of parallel arranged and fused spindles in male MII, resulting in the production of unreduced first division restitution 2n spores. Although JASON encodes a protein of unknown function, we additionally show that the meiotic ps defect in jason is caused by a reduction in AtPS1 transcript levels, indicating that JASON positively regulates AtPS1 expression, allowing the proper organization and orientation of metaphase II spindle plates in MII.

Use of 2n Gametes in Plant Breeding

“…Parallel, fused or tripolar spindles are different phenotypic expressions of this gene. A similar male-specific dyad-triad phenotype was observed and characterised in another mutant called jason (De Storme & Geelen, 2011;Erilova et al, 2009). Mutants of two other genes, OSD and TAM (CYCA1;2), were shown to omit the second meiotic division in both male and female sporogenesis at high frequency resulting in the formation of both 2n pollen and egg cells (d'Erfurth et al, 2009(d'Erfurth et al, , 2010.…”

Aberrant Classopollis pollen reveals evidence for unreduced (2 n ) pollen in the conifer family Cheirolepidiaceae during the Triassic–Jurassic transition

“…Principally, the observed pattern can be ascribed to the formation of anucleate, haploid and unreduced 2n pollen. In modern plants, pollen size is related to the number of chromosomes with increasing pollen volume at higher ploidy levels [9,[19][20][21][22][32][33][34][35]. While the number of pollen openings has been reported to vary in some polyploidy angiosperms [36], in this study, the number of pores and the furrows of Classopollis remains constant.…”

The Fate of Chromosomes and Alleles in an AllohexaploidBrassicaPopulation

“…Genetic factors related to unreduced gamete production in the parent plants (Mason et al 2011) may have been partially transmissible to the majority of (B. napus 3 B. carinata) 3 B. juncea SP progeny, based on comparison with the results of Iwasa (1964). Several mutations resulting in high frequencies of unreduced gamete formation have been identified in Arabidopsis (D 'Erfurth et al 2008;De Storme and Geelen 2011), and genetic factors have been implicated in other species (Tavoletti et al 1991). However, it is probable that univalent-induced meiotic restitution [the spread of univalents across the metaphase plate resulting in a restitution nucleus (Catcheside 1934;De Storme and Geelen 2013)] was responsible for the unreduced gamete that contributed to the allohexaploid plant A1.…”