Polyploidy and Evolution

Polyploidy and evolution have a strong connection. Polyploidy is not only one of the best-known evolutionary processes but also the most rapid method known to produce radically different vigorous and well-adapted genotypes.

In several instances, the resynthesis of polyploid species from the suspected diploid parent in the lab has been accomplished. This provides critical proof of the hypothesis that hybridization between species, followed by chromosome doubling, contributes to the formation of new species.

In many cases, polyploid species show definite advantages over their diploid ancestors. Stebbins regarded the induction of polyploidy as an evolutionary shortcut through which a genus can adapt more rapidly to the changing environment than by gene mutation or gene combination. Over time, the difference between the polyploid species and their ancestors may become sharp, and new species may be established.

Polyploidy and Evolution

Polyploids are significant in the evolution of crop plants and the origin of new species. They are usually fertile allopolyploids. They show increased vigour and resistance. In many cases, the interspecific and intraspecific hybridization will lead to sterility, but when polyploidy is induced in such plants, they will become fertile. Thus, new species are formed.

Clausia crossed closely related species of Nicotiana sylvestris and N. tomentosiformis and produced a sterile hybrid.
By induction of polyploidy, the hybrid was made fertile.
The fertile hybrid resembles the naturally occurring N. tobaccum, which is a new species.

Importance of Polyploidy in Evolution of Plants

Polyploidy results from the whole genome duplication of an organism, which happens due to premature cell cycle exit or cell-cell fusion.

Such a phenomenon often helps increase biological plasticity, better adaptation for the plants to their changing environment, stress-resistance, and regeneration.
These processes eventually lead to the formation of a new species that is suitable for the changing surroundings, eventually causing evolution.
Evolution through polyploidy is seen in characteristics such as transcription activation, response to stress, hypoxia, DNA damage, morphogenesis, longevity, etc.
Polyploidization (multiplication of the complete chromosome set) helps survive stressful situations through cell viability.
Evidence shows that plant genomes either silence or eliminate the duplicated genes after multiple polyploidization events, leading to more evolution to the newly formed genome.
They may also undergo reshuffling or fractionation of the genome.
As polyploidization alters the genome, these alterations differ with the basic constitution, thus resulting in sub-genomes.
The dominant sub-genomes in allopolyploids show less fractionation and have a higher gene density than their autopolyploid counterparts.
These dominant sub-genomes contain fewer transposon elements, thus preventing them from DNA methylation and a lesser impact by epigenetic effects. Therefore, their gene expression is higher, establishing their dominance.
Most often, genes that encode proteins for DNA metabolism, nuclease, RNA binding, etc, which function independently, lose their redundant copies of genes.
The surviving multiple copies of genes may undergo neo-functionalization, leading to innovative traits and functions.
On the other hand, the presence of duplicated copies of genes in many plants causes an imbalance that affects the plant’s fitness and might be eliminated through natural selection.
Polyploidy influences not only the morphological attributes of the individual but also has a profound effect on the reproductive potentiality and genetic variability of the progeny.
All these play an important role in evolution.

References

Agarwal, P. V. |. V. (2004). Cell biology, Genetics, Molecular Biology, Evolution, and Ecology: Evolution and Ecology. S. Chand Publishing.
Anatskaya, O. V., & Vinogradov, A. E. (2022). Polyploidy as a Fundamental Phenomenon in Evolution, Development, Adaptation and Diseases. International Journal of Molecular Sciences, 23(7), 3542. https://doi.org/10.3390/ijms23073542
Adams, K. L., & Wendel, J. F. (2005). Polyploidy and genome evolution in plants. Current Opinion in Plant Biology, 8(2), 135-141. https://doi.org/10.1016/j.pbi.2005.01.001
Zhang, K., Wang, X., & Cheng, F. (2019). Plant Polyploidy: Origin, Evolution, and Its Influence on Crop Domestication. Horticultural Plant Journal, 5(6), 231-239. https://doi.org/10.1016/j.hpj.2019.11.003