Although the evolutionary success of polyploidy in higher plants has been widely recognized, there is virtually no information on how polyploid genomes have evolved after their formation. In this report, we used synthetic polyploids of Brassica as a model system to study genome evolution in the early generations after polyploidization. The initial polyploids we developed were completely homozygous, and thus, no nuclear genome changes were expected in selffertilized progenies. (14) and the linkage orders of RFLP loci (15). However, these and other studies on polyploid evolution (5, 16) have compared natural polyploids, which are usually hundreds or thousands of years old, to present forms of hypothesized progenitors. Thus, it was not possible to distinguish between genome change after formation of the polyploid and genome divergence within the diploid progenitor species or to determine how quickly newly formed polyploid genomes evolve. Synthetic polyploids provide a model system to study early events in the evolution of polyploid genomes. Because the exact progenitors for a synthetic polyploid are known, we can determine precisely whether extensive genome changes occur after synthesis of polyploids and if so, the timing and processes of genome changes. We recently developed a series of synthetic Brassica polyploids by reciprocal interspecific hybridizations between the diploid species, followed by chromosome doubling of the F1 hybrids (17). We now report direct evidence for nuclear genome changes in these synthetic polyploids on the basis of comparing RFLP patterns of synthetic polyploids and their self-pollinated progenies by using a large number of cloned DNA probes.Polyploidy is one of the most distinctive and widespread modes of speciation in higher plants. Thirty to 70% of angiosperms, including many important crop plants, are estimated to have polyploidy in their lineages (1-6). The success ofpolyploid species has been attributed to their ability to colonize a wider range of habitats and to survive better in unstable climates compared with their diploid progenitors (7-10), presumably due to increased heterozygosity and flexibility provided by the presence of additional alleles (11-13). Genome multiplicity also provides a genetic buffer against the effects of individual alleles; and thus, new mutations are expected to contribute less to the evolution of polyploids compared to diploids (6). However, this hypothesis assumes that diploids and polyploids have equal mutation rates. It is possible that genome change is greatly accelerated in new polyploids derived from interspecies hybrids, due to greater instabilities created by the interaction of diverse genomes. Such changes could result in rapid genetic divergence of newly formed polyploids and might have contributed to the evolutionary success of many polyploid lineages.The potential contribution of genome change to the evolution of polyploids has been overlooked, mainly due to lack of information on how polyploid genomes have evolved after their for...
Toxoplasma gondii strains differ dramatically in virulence despite being genetically very similar. Genetic mapping revealed two closely adjacent quantitative trait loci on parasite chromosome VIIa that control the extreme virulence of the type I lineage. Positional cloning identified the candidate virulence gene ROP18, a highly polymorphic serine-threonine kinase that was secreted into the host cell during parasite invasion. Transfection of the virulent ROP18 allele into a nonpathogenic type III strain increased growth and enhanced mortality by 4 to 5 logs. These attributes of ROP18 required kinase activity, which revealed that secretion of effectors is a major component of parasite virulence.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.