Many plant species can produce offspring by self-fertilization (selfing). Self-fertilization with its own pollen can result in lower fitness due to negative effects of inbreeding. However, selfing may be advantageous when mating partners or pollinators are scarce. Such conditions exert a strong evolutionary pressure under which selfing may increase rapidly – this hypothesis was developed by Charles Darwin as early as 1876. Using the model plant thale cress (Arabidopsis thaliana), an international team of researchers (from Switzerland, Japan and Germany) led by Dr. Kentaro Shimizu at the University of Zurich now provides support for Darwin’s hypothesis. The research project was funded by the University Research Priority Program in Systems Biology/Functional Genomics.
Self-compatibility due to disrupted recognition gene
During the glacial periods, Arabidopsis thaliana survived only in warmer regions such as the Iberian Peninsula. As the ice sheets melted, Arabidopsis thaliana expanded its geographic range to cover most of Europe. Such rapid range expansion tends to be accompanied by a lack of mating partners and/or pollinators. Individual plants incurring spontaneous mutations resulting in self-compatibility now had an evolutionary advantage.
Self-incompatible plants prevent self-fertilization with a self-recognition system: SRK protein in the female style recognizes SCR protein in the self-pollen (male) and rejects these pollen grains. Arabidopsis thaliana, however, is self-compatible. It was not clear how self-compatibility evolved. In their article published in the journal Nature, Dr. Shimizu, a PhD student Takashi Tsuchimatsu, and their colleagues show that the SCR gene of Arabidopsis thaliana lost its function relatively recently – most likely during the climatic cycles of glacial and interglacial periods. The researchers exploited a plant variant originally collected in Weiningen (canton Zurich, Switzerland), because it carried an intact female SRK gene unlike most others. The colleagues in Japan led by Dr. Masao Watanabe succeeded in restoring its male SCR gene, effectively reversing evolution and thus artificially making Arabidopsis thaliana self-incompatible again.
The rapid evolution of self-fertilization may enable the survival of a species. However, it also entails risks because the evolution of selfing is almost always irreversible – an important insight in view of the current global climate warming. Generally, the genetic changes in plant and animal species brought about by climate change might not be reversed, even if climate change could be reversed. Evolutionary organismal responses due to climate change have not yet been sufficiently investigated. In order to investigate them, Dr. Shimizu has just started a joint project with ETH Zurich and WSL (Swiss Fedeal Institute for Forest, Snow and Landscape Research) funded by the Swiss National Science Foundation, to study genome-wide variation in alpine plants.
Takashi Tsuchimatsu, Keita Suwabe, Rie Shimizu-Inatsugi, Sachiyo Isokawa, Pavlos Pavlidis, Thomas Städler, Go Suzuki, Seiji Takayama, Masao Watanabe & Kentaro K. Shimizu, Evolution of self-compatibility in Arabidopsis by a mutation in the male specificity gene, Nature, DOI 10.1038/nature08927