Doubled-haploid induction generates extensive differential DNA methylation in Arabidopsis.

Doubled haploids (DHs) fix traits from hybrids in one generation. DH induction includes two changes in ploidy levels typically associated with variation in DNA methylation. However, DNA methylation patterns in DH plants and their biological significance are largely unknown. We generated three DH lines in Arabidopsis thaliana by crossing a haploid inducer with the accession Col-0, thus removing tissue culture and hybridization as a variable. DH induction produced thousands of differentially DNA methylated regions (DMRs), most of which were stochastic. Both haploidization and colchicine-induced genome duplication produced DMRs; the former mainly yielded DMRs at non-CG contexts, whereas the latter affected differential gene body methylation. Spontaneous genome doubling of haploid plants also induced DMRs in greater numbers than self-propagation. Our results provide the first evidence that haploid induction and genome doubling result in differential DNA methylation, offering a novel approach to induce epialleles.

Meiocyte size is a determining factor for unreduced gamete formation in Arabidopsis thaliana.

Polyploidy, the presence of more than two sets of chromosomes within a cell, is a widespread phenomenon in plants. The main route to polyploidy is considered through the production of unreduced gametes that are formed as a consequence of meiotic defects. Nevertheless, for reasons poorly understood, the frequency of unreduced gamete formation differs substantially among different plant species. The previously identified meiotic mutant jason (jas) in Arabidopsis thaliana forms about 60% diploid (2n) pollen. JAS is required to maintain an organelle band as a physical barrier between the two meiotic spindles, preventing previously separated chromosome groups from uniting into a single cell. In this study, we characterized the jas suppressor mutant telamon (tel) that restored the production of haploid pollen in the jas background. The tel mutant did not restore the organelle band, but enlarged the size of male jas tel meiocytes, suggesting that enlarged meiocytes can bypass the requirement of the organelle band. Consistently, enlarged meiocytes generated by a tetraploid jas mutant formed reduced gametes. The results reveal that meiocyte size impacts chromosome segregation in meiosis II, suggesting an alternative way to maintain the ploidy stability in meiosis during evolution.