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We are interested in studying the mechanisms of intercellular communication which are unique to plants. To answer the basic question of how plants recognize external signals and how these signals are transmitted into cells, we are conducting research to elucidate the molecular mechanisms of the following phenomena.
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1 ) Mechanisms of self-incompatibility in plants
Self-incompatibility (SI) is a genetic system used by many flowering plants to prevent self-fertilization and thereby generate and maintain genetic diversities within the species. Our laboratory has been studying the molecular mechanisms of SI in plants of the Brassicaceae and Solanaceae families.
We found that self/nonself recognition in the Brassicaceae is mediated by the direct interaction between pollen ligand and pistil receptor kinase (Fig. 1). Currently, we are working to elucidate the downstream signaling cascade leading to the rejection of self-pollen. The downstream events of SI (incompatible pathway) would be to interrupt the events that promote successful pollen germination and tube growth (compatible pathway). Thus, we are also working to identify the key components working in this compatible pathway by using Arabidopsis thaliana, a self-compatible model plant in the Brassicaceae.
For SI in the Solanaceae and Rosaceae families, we have proposed a model in which cytotoxic pistil ribonuclease is specifically degraded through proteasome pathway in non-self pollen tubes. Recently, we found that pollen elements are multiple F-box proteins that are expected to collaboratively detoxify non-self rebonucleases. We are now testing the validity of this model (Fig. 2).
2 ) Mechanisms of monoallelic gene expression in plants
A diploid organism has two copies of each genes, one inherited from each parent. Although majority of genes are expressed equally from both alleles, recent studies suggest that lots of genes frequently show monoallelic expression, although the underlying molecular mechanisms are unknown. These widespread monoallelic expressions receive much attention because these affect diversity in gene expression and phenotypic variation and onset of disease.
During studying dominant/recessive relationships between self-incompatibility genes, we found that the expression of recessive allele was suppressed by small RNA derived from dominant allele. We are now conducting studies to further clarify the mechanism of this epigenetic monoallelic expression system (Fig. 3).
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- Kubo et al., Science, 330, 796-799, 2010
- Tarutani et al., Nature, 466, 983-986, 2010
- Kakita et al. Plant Cell, 19, 3961-3973, 2007
- Shimosato et al. Plant Cell, 19, 107-117, 2007
- Shiba et al., Nature Genet., 38, 297-299, 2006
- Takayama and Isogai, Annu. Rev. Plant. Biol., 56, 467-489, 2005
- Murase et al., Science, 303, 1516-1519, 2004
- Shiba et al., Plant Cell, 14, 491-504, 2002
- Takayama et al., Nature, 413, 534-538, 2001
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Fig. 1 Mechanism for self-incompatibility in the Brassicaceae
Fig. 2 Mechanism for self-incompatibility in the Solanaceae
Fig. 3 Models for epigenetic control of dominant/recessive relationship
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