New research uncovers overlooked evolutionary shifts in pollen biology during transitions to self-fertilization.
In flowering plants, the transition from cross-fertilization (outcrossing) to self-fertilization has evolved repeatedly across species. This shift is often accompanied by a well-known set of traits collectively called the “selfing syndrome,” including smaller flowers and reduced scent. However, a new study highlights that important—but largely overlooked—changes also occur at the microscopic level of pollen biology.
Researchers from the Faculty of Science at Charles University and The Institute of Experimental Botany of the Czech Academy of Sciences (IEB) investigated how self-fertilization affects the pollen coat, a thin outer layer of pollen grains that plays a crucial role in successful reproduction, particularly in interactions between pollen and the female reproductive organs. The team compared pollen coat thickness and protein composition (proteomes) between self-fertilizing and outcrossing species in the plant genera Arabidopsis and Capsella. These groups provide a unique opportunity to study evolution, as they include three independent transitions to self-fertilization.
The findings reveal that pollen coat thickness tends to decrease over evolutionary time following the shift to selfing. Significant reductions were observed in Arabidopsis thaliana and Capsella rubella, both of which exhibit clear selfing syndrome traits. In contrast, Arabidopsis lyrata, which represents a more recent transition and lacks the full selfing syndrome, showed no such reduction.
Beyond structural changes, the study also uncovered patterns in pollen coat proteins. Certain proteins showed consistent differences in abundance between selfing and outcrossing species more often than expected by chance. Interestingly, the direction of these changes was not uniform across species, suggesting a complex and flexible evolutionary response.
Many of these proteins are currently annotated as being involved in pathogen defense due to their structural characteristics. However, the researchers propose that they likely play a previously underappreciated role in pollen–pistil interactions, a key process in plant reproduction.
Overall, the study points to limited but meaningful convergent evolution in pollen traits following the transition to self-fertilization. It also identifies a group of understudied pollen coat proteins that appear to be hotspots of evolutionary change.
These findings open new avenues for understanding how plants adapt their reproductive strategies and highlight the importance of looking beyond visible traits to uncover hidden layers of evolutionary innovation.
İltaş, Ö., Salomon, L., Kovačik, M., Čertner, M., Talacko, P., Harant, K., Hafidh, S. and Lafon Placette, C. (2026), The abundance of pollen coat small signaling proteins shows limited convergence between independent selfing transitions in Arabidopsis and Capsella. New Phytol. https://doi.org/10.1111/nph.71167
