Research on interspecific reproduction barriers in plants
Plants rely on pollinators to reproduce. However, vectors carry a variety of pollens, including those of the same species, different species, or even pathogens. This is a serious problem for plants, and it has been reported that for some plants in natura, the majority of the pollen carried originates from different species. Pollen of different species is often disadvantageous for plant reproduction, so plants have a sophisticated mechanism to filter out all the miscellaneous pollen that is carried and select only pollen of the same species. We are exploring such molecular mechanisms. Elucidating these mechanisms is important for understanding how ecosystems are formed.
On the other hand, research on interspecific reproductive barriers is very important for agriculture. For example, the bread wheat we commonly eat was created through artificial crossbreeding between two different species. However, cross-species hybridization like this is not easy, and success stories are rare. By understanding the mechanism, we aim to develop technology to artificially create new environmentally adaptable crops that combine the best of both species.
I want to know more
Research on reproductive barriers in plants has been active since Darwin's time, and is even described in ``On the Origin of Species.'' However, the molecular mechanism was not understood until recently. We have revealed that a cell membrane protein called Stigmatic Privacy 1 (SPRI1, meaning "Privacy also exists in Plant Pistils") plays a key role in the reproductive barrier. When SPRI1 was genetically disrupted, pollen from other species was observed to enter the pistil. Furthermore, the transcription factor SPRI2 has also been found to be a regulatory factor that creates interspecies barriers. These discoveries are world firsts and clearly demonstrate that reproductive barriers can be artificially modified. A key factor in the interspecies barrier has also been discovered in zebrafish and has been named as Bouncer. It may be possible to discover a common underlying principle between animals and plants in the near future.
Have you ever looked at a roadside plant or a plant you are growing at home and wondered: ”Can see flowers, but no seeds”.
This may be due to a phenomenon called "self-incompatibility" of plants. More than half of the plants on Earth do not produce seeds using their own pollen to prevent inbreeding. Although plants do not move, it is becoming clear that they have a "lock and keyhole" mechanism made up of molecules such as proteins and RNA, which allows them to distinguish between self and non-self.
We are researching the mechanism of self-incompatibility. We have elucidated the molecular mechanisms of self-incompatibility in various plants, including S-RNase and SLF, which are used by many other plants in the Solanaceae family, and SP11 and SRK, which are used by Brassicaceae plants. Elucidating these mechanisms will reveal how immobile plants maintain diversity in the ecosystem and adapt to the global environment, and will also lead to new crop development technologies that utilize these properties.
I want to know more
Research on self-incompatibility has a long history, and various things have been discovered. Surprisingly, self-incompatibility has been found in sessile animals such as sea squirts and corals, and research is progressing in these organisms too, and similarities and differences with plants are becoming clearer. Our laboratory will be releasing videos explaining the complex and interesting world of self-incompatibility, as well as videos introducing research results.
Research on the basic mechanism of plant reproduction
For some people, hearing the word "pollen" may evoke unpleasant memories such as allergies. However, pollen is a cell that contains various hidden features of plants, and the interaction between pollen and pistil cells is a unique biological phenomenon. For example, pollen is produced in the stamens, but it does not know when they can reach the pistils and fertilize. In some cases, they are carried over very long distances by pollinators. Therefore, pollen must possess the ability to withstand various stresses such as ultraviolet rays and dryness, and it should remain in a kind of dormant state. On the other hand, the pollen that has attached to the pistil extends a pollen tube toward the ovule (the organ that contains the egg cell) and competes in a harsh race for fertilization. Only those that quickly elongate their pollen tubes can leave offspring. In other words, pollen must have the contradictory properties of dormancy and explosive growth.
After pollen attaches to the pistil, it transfers the protein and lipid mixture on the surface called the pollen coat to the pistil. This pollen coat contains a protein called Glycine Rich Protein (GRP), and it is said that there are other signal substances that are transferred to the pistil, but many of them have not yet been discovered.
Research on symbiosis and competition between flowers and microorganisms
Flowers are essential for producing our food such as seeds and honey, but they are also hubs where a variety of living things come and go. For example, insects visit flowers in search of nectar and pollen, but at the same time, microorganisms such as bacteria and fungi are also carried from flower to flower, forming a unique ecosystem. There are various interactions between these microorganisms and plants via substances, and various molecules such as biological defense substances and host-modifying substances are active. We aim to elucidate biologically active substances from plants and microorganisms by focusing on symbiotic and competitive relationships mediated by flowers. By focusing on these unique interactions between organisms, we aim to discover substances with unprecedented new functions and contribute to the understanding and maintenance of complex ecosystems mediated by insects, plants, and microorganisms.
For famous chemical substances discovered long ago, such as plant hormones, a field called chemical biology has been developed to freely control the activity within plants using receptors and derivatives. However, few compounds have been found to control biological phenomena such as plant reproduction, where many of the mechanisms are unknown or have only recently been revealed. Plant reproduction is an important phenomenon for breeding and maintaining ecosystems, so there are great expectations for the development of “reproductive chemicals”.
In our laboratory, we are searching for natural products that control the self-incompatibility and the activity of the reproductive key molecules of the reproductive barrier that we have discovered so far. Furthermore, through collaborative research with synthetic organic chemists, we are developing artificial molecules that control reproduction. Developing molecules that control reproduction will not only lead to the establishment of new agricultural systems, but will also deepen our understanding of biological phenomena.
Our laboratory was established in 1924, and has since expanded to investigate plant hormones such as gibberellins, antibiotics, plant growth regulators, microbial pheromones, insect hormones, plant reproductive factors, marine organisms, biomineralization etc. The subjects of our research cover many groups of organisms that encompass biodiversity, and it is no exaggeration to say that ultimately we are studying ”ecosystems”,.
Based on this idea, we currently consider whether we can directly approach complex living systems such as ecosystems from the perspective of bioorganic chemistry. We believe that artificial biotopes and flower ecospheres are suitable models for such research, and we plan to use an interdisciplinary approach. This research is still in the early stages, but we are looking for interested students, graduate students, and collaborators.
