Partial redundancy buffers deleterious effects of mutatingDNA methyltransferase 1-1(MET1-1) in polyploid wheat

Abstract

AbstractDNA methylation is conserved across biological kingdoms, playing important roles in gene expression, transposable element silencing and genome stability. Altering DNA methylation could generate additional phenotypic variation for crop breeding, however the lethality of epigenetic mutants in crop species has hindered its investigation. Here, we exploit partial redundancy between homoeologs in polyploid wheat to generate viable mutants in the DNAmethyltransferase 1-1(MET1-1) gene with altered methylation profiles. In bothTriticum turgidum(tetraploid wheat) andTriticum aestivum(hexaploid wheat) we identified clear segregation distortions of higher-order mutants (5/6 and 6/6 mutantmet1-1copies in hexaploid and 3/4 and 4/4 copies in tetraploid) when genotyping segregating seeds and seedlings, which we attribute to reduced transmission of null mutant gametes. We found that the reduced transmission occurred from both the maternal and paternal gametes, however, we did not detect any deleterious effects on pollen development. The loss of four or more functional copies ofMET1-1results in decreased CG methylation in hexaploid wheat. Changes to gene expression increase stepwise with the number of mutant alleles suggesting a dosage dependent effect. Finally, we identify heritable changes to flowering and awn phenotypes which segregate independently ofMET1-1. Together our results demonstrate that polyploidy can be leveraged to generate quantitative changes to CG methylation without the lethal consequences observed in other crops, opening the potential to exploit novel epialleles in plant breeding.