Arabidopsis species hybrids in the study of species differences and evolution of amphiploidy in plants

It is estimated that 5 million years of evolution separate Arabidopsis thal iana from its close relative Arabidopsis lyrata. The two taxa differ by man y characteristics, and together they exemplify the differentiation of angio sperms into self-fertilizing and cross-fertilizing species as well as annua l and perennial species. Despite their disparate life histories, the two sp ecies can be crossed to produce viable and vigorous hybrids exhibiting hete rotic effects. Although pollen sterile, the hybrids produce viable ovules a nd were used as female parent in backcrosses to both parental species. The resulting backcross plants exhibited transgressive variation for a number o f interesting developmental and growth traits as well as negative nuclear/c ytoplasmic interactions. Moreover, the genesis of a fertile amphidiploid ne ospecies, apparently by spontaneous somatic doubling in an interspecific hy brid, was observed in the laboratory. The mechanisms responsible for the ge neration of amphiploids and the subsequent evolution of amphiploid genomes can now be studied through direct observation using the large arsenal of mo lecular tools available for Arabidopsis.