# Seiji Takayama

**Seiji Takayama** (高山 誠司) is a Japanese plant molecular biologist who studies self-incompatibility, the mechanism flowering plants use to reject their own pollen, and the related interspecific barriers that keep pollen of one species out of another. He is a specially appointed researcher (特任研究員) at the University of Tokyo Graduate School of Agricultural and Life Sciences, a position the KAKEN researcher database records for 2024–2026 after his tenure as professor there.<sup>[1](https://nrid.nii.ac.jp/nrid/1000070273836/)</sup> His laboratory defined the molecular actors of self-incompatibility in the [Brassicaceae](https://www.edgepedia.org/brassicaceae), the cabbage family, and showed that the [Solanaceae](https://www.edgepedia.org/solanaceae), the nightshade family, run a fundamentally different version of the same barrier.<sup>[2](https://www.nature.com/articles/35097104)</sup><sup> • </sup><sup>[3](https://bsw3.naist.jp/eng/research/index.php?id=1882)</sup>

| Fact | Detail |
|---|---|
| Current position | Specially appointed researcher, Graduate School of Agricultural and Life Sciences, University of Tokyo (2024–2026)<sup>[1](https://nrid.nii.ac.jp/nrid/1000070273836/)</sup> |
| Professor, University of Tokyo | October 2016 to March 2024, Applied Biological Chemistry program<sup>[4](https://www.u-tokyo.ac.jp/content/400231722.pdf)</sup> |
| Professor, NAIST | January 2006 to 2016, Graduate School of Biological Sciences<sup>[4](https://www.u-tokyo.ac.jp/content/400231722.pdf)</sup> |
| Training | BS (1981) and Doctor of Agriculture (1986), University of Tokyo, agricultural chemistry<sup>[4](https://www.u-tokyo.ac.jp/content/400231722.pdf)</sup> |
| Industry career | Researcher, Ajinomoto Co. Central Research Laboratory, from April 1986<sup>[4](https://www.u-tokyo.ac.jp/content/400231722.pdf)</sup> |
| Signature work | "Direct ligand–receptor complex interaction controls Brassica self-incompatibility", Nature, 2001<sup>[2](https://www.nature.com/articles/35097104)</sup> |
| Award | 66th Fujiwara Award, Fujiwara Science Foundation, June 2025<sup>[5](https://www.a.u-tokyo.ac.jp/news/news_20250618-1.html)</sup> |

## Career

Takayama graduated from the University of Tokyo Faculty of Agriculture, Department of Agricultural Chemistry, in March 1981 and completed the doctoral program in March 1986, receiving the degree of [Doctor](https://www.edgepedia.org/doctor-title) of Agriculture.<sup>[4](https://www.u-tokyo.ac.jp/content/400231722.pdf)</sup> He joined Ajinomoto Co.'s Central Research Laboratory as a researcher in April 1986; according to the 1987 Nature paper on Brassica S-glycoprotein sequences, that work appeared during this industry period.<sup>[4](https://www.u-tokyo.ac.jp/content/400231722.pdf)</sup><sup> • </sup><sup>[6](https://doi.org/10.1038/326102a0)</sup> 

In April 1995 he moved to academia as associate professor at the Nara Institute of Science and Technology (NAIST) Graduate School of Biological Sciences, becoming professor there in January 2006.<sup>[4](https://www.u-tokyo.ac.jp/content/400231722.pdf)</sup> At NAIST he led the KAKENHI targeted project "Molecular analysis of the genome barriers in the early reproductive process" (grant 18075008, 2006–2010).<sup>[7](https://naist.repo.nii.ac.jp/records/1005)</sup> He was appointed professor at the University of Tokyo Graduate School of Agricultural and Life Sciences in October 2016, in the Bio-organic Chemistry laboratory of the Applied Biological Chemistry program, and served until March 2024.<sup>[4](https://www.u-tokyo.ac.jp/content/400231722.pdf)</sup> He then took up the specially appointed researcher post he holds in 2026.<sup>[1](https://nrid.nii.ac.jp/nrid/1000070273836/)</sup>

## Self-incompatibility in the Brassicaceae

Self-incompatibility (SI) prevents self-fertilization: a single S-locus carries multiple haplotypes, and when pistil and pollen share the same S-haplotype the pollen is recognized as self and rejected.<sup>[8](https://pmc.ncbi.nlm.nih.gov/articles/PMC11170026/)</sup> In the Brassicaceae the S-locus contains three highly polymorphic genes: **S-receptor kinase (SRK)**, **S-locus protein 11 (SP11)**, also called SCR, and **S-locus glycoprotein (SLG)**. SRK encodes a membrane-spanning serine/threonine kinase that determines the S-haplotype specificity of the stigma; SP11 encodes a small cysteine-rich protein that determines the S-haplotype specificity of pollen.<sup>[2](https://www.nature.com/articles/35097104)</sup> The system is thus a ligand–receptor pair: the pollen coat delivers SP11, and the stigma papilla cell carries SRK.

Recognition triggers a signaling cascade in the papilla cell. Three direct interactors of SRK are the THIOREDOXIN H-LIKE proteins THL1 and THL2, the M-locus protein kinase (MLPK), and the E3 ubiquitin ligase ARC1.<sup>[9](https://pmc.ncbi.nlm.nih.gov/articles/PMC10873884/)</sup> On the compatible side, Brassicaceae pollen coat contains factors that induce actin filament rearrangement in same-species papilla cells and secretion of Ca²⁺-containing water to the pollen; these reactions are inhibited by the SI signaling pathway.<sup>[7](https://naist.repo.nii.ac.jp/records/1005)</sup>

Brassicaceae SI is sporophytically controlled, and S-haplotypes show dominant and recessive relationships, particularly on the pollen side: an SaSb heterozygote with dominant Sa exhibits only the Sa pollen phenotype.<sup>[8](https://pmc.ncbi.nlm.nih.gov/articles/PMC11170026/)</sup>

## Representative work

The 1987 S-glycoprotein sequences. The paper "Sequences of S-glycoproteins, products of the Brassica campestris self-incompatibility locus", published in Nature on 1 March 1987, with Takayama of the [University of Tokyo](https://www.edgepedia.org/university-of-tokyo) among the authors, provided the sequences of the stigma proteins encoded at the S-locus.<sup>[6](https://doi.org/10.1038/326102a0)</sup>

The 2001 ligand–receptor papers. Two 2001 papers settled the identity of the pollen ligand and its receptor interaction. Takayama's first-author Nature paper showed that a single form of SP11 of the S8 haplotype (S8-SP11), stabilized by four intramolecular disulphide bonds, specifically binds the stigma membrane of the S8 haplotype to induce autophosphorylation of SRK8, and that SRK8 and SLG8 together form a high-affinity receptor complex for S8-SP11.<sup>[2](https://www.nature.com/articles/35097104)</sup> 

The 2010 small-RNA dominance mechanism. The Nature paper "Trans-acting small RNA determines dominance relationships in Brassica self-incompatibility" (Nature 466, 983–986, 2010) showed that two small RNAs, SP11 methylation inducer (SMI) and SMI2, regulate the dominant–recessive hierarchy on the pollen side by suppressing SP11 expression.<sup>[9](https://pmc.ncbi.nlm.nih.gov/articles/PMC10873884/)</sup>

The 2005 synthesis. Takayama's review "Self-Incompatibility in Plants" (Annual Review of Plant Biology 56: 467–489, 2005), co-authored with a colleague, framed the field's major SI mechanisms: in the Brassicaceae a pollen ligand and stigmatic receptor kinase whose interaction induces incompatible signaling in stigma papilla cells; in the Solanaceae a ribonuclease and an F-box protein, suggesting involvement of RNA and protein degradation; and in the [Papaveraceae](https://www.edgepedia.org/papaveraceae) a female determinant triggering Ca²⁺-dependent pollen death.<sup>[10](https://www.annualreviews.org/content/journals/10.1146/annurev.arplant.56.032604.144249)</sup> 

## Later research: Solanaceae and interspecific barriers

In [Petunia](https://www.edgepedia.org/petunia) (Solanaceae), Takayama's team found that the S-locus encodes multiple types of SLF proteins, each recognizing a subset of non-self S-RNases, a **collaborative non-self recognition** system; the work appeared in Science as a Research Article on 5 November 2010 with an accompanying perspective.<sup>[3](https://bsw3.naist.jp/eng/research/index.php?id=1882)</sup> The comparison is stark: Brassicaceae adopt a self-recognition system, in which pollen carrying the same S-haplotype as the pistil is rejected, whereas Solanaceae use a collaborative nonself-recognition system, in which pollen is accepted only when its SLF set detoxifies all non-self S-RNases.<sup>[8](https://pmc.ncbi.nlm.nih.gov/articles/PMC11170026/)</sup>

His recent work maps the barriers that separate species. A 2025 study showed that transgenic [Arabidopsis](https://www.edgepedia.org/arabidopsis) with reduced stigmatic cutin (waxy polymer in plant surfaces, forming the cuticle) still rejected self-incompatible pollen, so cutin does not contribute to SI, but heterospecific pollen rejection was significantly impaired, and the cutin-based barrier functions independently of the STIGMATIC PRIVACY 1 protein barrier, suggesting multiple independent mechanisms for interspecific pollen rejection.<sup>[11](https://researchmap.jp/read0187851/published_papers/52834033)</sup>

## Recent developments

According to the University of Tokyo's introduction of faculty retiring in FY2023, Takayama retired from his professorship in March 2024 and continues as a specially appointed researcher.<sup>[4](https://www.u-tokyo.ac.jp/content/400231722.pdf)</sup><sup> • </sup><sup>[1](https://nrid.nii.ac.jp/nrid/1000070273836/)</sup> In April 2024 he published, with co-authors, a review of self-incompatibility in Brassicaceae and Solanaceae in Proceedings of the Japan Academy, Series B (100(4): 264–280).<sup>[8](https://pmc.ncbi.nlm.nih.gov/articles/PMC11170026/)</sup> In June 2025 the university announced that he, as professor emeritus, received the 66th Fujiwara Award from the Fujiwara Science Foundation for research on self-incompatibility and interspecific incompatibility in sexual reproduction; the citation recognized that he showed SI uses diverse molecular mechanisms including ligand–receptor type and toxin–antitoxin type, and first demonstrated a "non-self recognition" system in addition to the previously known self-rejection type.<sup>[5](https://www.a.u-tokyo.ac.jp/news/news_20250618-1.html)</sup> He was principal investigator of the KAKENHI project "Integrated understanding of interspecific-incompatibility and self-incompatibility in the Brassicaceae" (21H05030), which ran from 5 July 2021 to 31 March 2026 with total funding of 189,930 thousand yen; its outputs include 9 journal papers, 48 conference presentations, and one patent (2022, a method for producing self-compatible Brassicaceae plants).<sup>[12](https://kaken.nii.ac.jp/ja/grant/KAKENHI-PROJECT-21H05030/)</sup>

## Applications

According to a 2024 review in the Proceedings of the Japan Academy, Series B, most common Brassicaceae vegetables, including Chinese cabbage, cabbage, broccoli, and radish, are grown from [F1 hybrid](https://www.edgepedia.org/f1-hybrid) seeds produced by crossing two genetically different inbred lines using the property of SI.<sup>[8](https://pmc.ncbi.nlm.nih.gov/articles/PMC11170026/)</sup> SI is widely used for hybrid seed production in the self-incompatible diploid vegetables [Brassica oleracea](https://www.edgepedia.org/brassica-oleracea) and B. rapa/B. campestris, while the amphidiploid oilseed rape B. napus is naturally self-compatible and requires introgression of S-alleles from parental species.<sup>[13](https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2020.00195/full)</sup> The university's award announcement notes applications in biodiversity conservation, F1 hybrid seed production, and interspecific hybrid breeding.<sup>[5](https://www.a.u-tokyo.ac.jp/news/news_20250618-1.html)</sup>

## References

1. KAKEN, Researchers | Takayama Seiji (70273836). https://nrid.nii.ac.jp/nrid/1000070273836/
2. Takayama, S. et al. Direct ligand–receptor complex interaction controls Brassica self-incompatibility. Nature (2001). https://www.nature.com/articles/35097104
3. Novel Non-Self Recognition System That Prevents Inbreeding in Solanaceous Plants. NAIST. https://bsw3.naist.jp/eng/research/index.php?id=1882
4. 令和5年度退職教員の紹介 (University of Tokyo). https://www.u-tokyo.ac.jp/content/400231722.pdf
5. 高山誠司名誉教授が第66回藤原賞を受賞. University of Tokyo Graduate School of Agricultural and Life Sciences (2025). https://www.a.u-tokyo.ac.jp/news/news_20250618-1.html
6. Sequences of S-glycoproteins, products of the Brassica campestris self-incompatibility locus. Nature (1987). https://doi.org/10.1038/326102a0
7. 初期受粉過程における生殖障壁の分子解析. NAIST institutional repository. https://naist.repo.nii.ac.jp/records/1005
8. Takayama, S., Murase, K., Isogai, A. Molecular mechanisms of self-incompatibility in Brassicaceae and Solanaceae. Proc. Japan Acad. Ser. B (2024). https://pmc.ncbi.nlm.nih.gov/articles/PMC11170026/
9. Molecular insights into self-incompatibility systems: From evolution to breeding. Plant Communications (2024). https://pmc.ncbi.nlm.nih.gov/articles/PMC10873884/
10. Takayama, S. and Isogai, A. Self-Incompatibility in Plants. Annual Review of Plant Biology 56 (2005). https://www.annualreviews.org/content/journals/10.1146/annurev.arplant.56.032604.144249
11. Cuticle layer forms a reproductive barrier in the Brassicaceae (2025). https://researchmap.jp/read0187851/published_papers/52834033
12. KAKEN, アブラナ科植物の種間不和合性と自家不和合性の統合的理解 (21H05030). https://kaken.nii.ac.jp/ja/grant/KAKENHI-PROJECT-21H05030/
13. Self-(In)compatibility Systems: Target Traits for Crop-Production, Plant Breeding, and Biotechnology. Frontiers in Plant Science (2020). https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2020.00195/full

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*Topic: Encyclopedia › Life and health › Life and health scientists › Life scientists › Researchers in developmental biology, stem cells, and plant biology › Plant genetics, genomics, and pathology*

*Initially written Sep 21, 2026 · Reviewed: Sep 25, 2026; Sep 30, 2026 · Edited: Sep 25, 2026; Sep 30, 2026; Oct 11, 2026; Oct 15, 2026 · Last review: Sep 30, 2026*

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