Multi-species polyploidization, chromosome shuffling, and genome extraction inZea/Tripsacumhybrids

Abstract

By hybridization and special sexual reproduction, we sequentially aggregatedZea mays,Zea perennis, andTripsacum dactyloidesin an allohexaploid, backcrossed it with maize, derived self-fertile allotetraploids of maize andZ. perennisby natural genome extraction, extended their first six selfed generations, and finally constructed amphitetraploid maize using nascent allotetraploids as a genetic bridge. Transgenerational chromosome inheritance, subgenomes stability, chromosome pairings and rearrangements, and their impacts on an organisms fitness were investigated by fertility phenotyping and molecular cytogenetics techniques GISH and FISH. Results showed that diversified sexual reproductive methods produced highly differentiated progenies (2n=35-84) with varying proportions of subgenomic chromosomes, of which one individual (2n=54, MMMPT) overcame self-incompatibility barriers and produced self-fertile nascent near-allotetraploid by preferentially eliminatingTripsacumchromosomes. Nascent near-allotetraploid progenies showed persistent chromosome changes, intergenomic translocations, and rDNA variations for at least up to the first six selfed generations; however, ploidy tended to stabilize at near-tetraploid level (2n=40) with full integrity of 45SrDNA pairs, and a trend of decreasing variations by advancing generations with an average of 25.53, 14.14, and 0.37 maize,Z. perennis, andT. dactyloideschromosomes, respectively. The mechanisms for three genome stabilities and karyotype evolution for formatting new polyploid species were discussed.