Abstract
Short periods of cold stress induce male meiotic restitution and diploid pollen formation in Arabidopsis thaliana by specifically interfering with male meiotic cytokinesis. Similar alterations in male meiotic cell division and gametophytic ploidy stability occur when gibberellic acid (GA) signaling is perturbed in developing anthers. In this study, we found that exogenous application of GA primarily induces second division restitution (SDR)-type pollen in Arabidopsis, similar to what cold does. Driven by the close similarity in cellular defects, we tested the hypothesis that cold-induced meiotic restitution is mediated by GA-DELLA signaling. Using a combination of chemical, genetic and cytological approaches, however, we found that both exogenously and endogenously altered GA signaling do not affect the cold sensitivity of male meiotic cytokinesis. Moreover, in vivo localization study using a GFP-tagged version of RGA protein revealed that cold does not affect the expression pattern and abundance of DELLA in Arabidopsis anthers at tetrad stage. Expression study found that transcript of RGA appears enhanced in cold-stressed young flower buds. Since our previous work demonstrated that loss of function of DELLA causes irregular male meiotic cytokinesis, we here conclude that cold-induced meiotic restitution is not mediated by DELLA-dependent GA signaling.
Highlights
The production of viable haploid gametes is vital for the fertility and ploidy stability of flowering plants
first division restitution (FDR)/second division restitution (SDR) genotyping of gibberellic acid (GA) Primarily Induces SDR-Type Male Meiotic Restitution In Arabidopsis, recombination hotspots are distributed along entire chromatin except for centromeric regions (Salomé et al, 2011)
Because we have previously shown that GA treatment may induce around 5% meiotic restitution (Liu et al, 2017b), we here only quantified the number of meiotic restituted products and classified them into either FDR- or SDR-type (Supplementary Table S1)
Summary
The production of viable haploid gametes is vital for the fertility and ploidy stability of flowering plants. Meiotic restitution can be classified into either FDR or SDR according to the genetic make-up of the yielded unreduced gametes (Kohler et al, 2010). FDR-type unreduced gametes maintain parental heterozygosity in genomic regions where meiotic recombination occurs rarely. In SDR-type meiotic restitution, homologous chromosomes segregate but sister chromatids are grouped into unreduced gametes, which typically leads to heterozygosity at recombination-free chromatin regions (De Storme and Geelen, 2013b). Meiotic restitution and associated formation of unreduced gametes can be induced either through specific genetic defects or by temperature stress. In Arabidopsis thaliana, for example, cold stress causes male meiotic restitution (primarily SDR-type) by disrupting the organization of RMAs at the end of male meiosis, resulting in incomplete meiotic cytokinesis and unreduced gamete formation (De Storme et al, 2012)
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