Laboratories

Intercellular Communications

Outline of Research and Education

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.

Major Research Topics

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 diversity 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/non-self 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-pollination. 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 at work 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 ribonucleases. We are now testing the validity of this model (Fig. 2).

Mechanisms of monoallelic gene expression in plants

A diploid organism has two copies of each gene, one inherited from each parent. Although the majority of genes is expressed equally from both alleles, recent studies suggest that genes frequently show monoallelic expression, although the underlying molecular mechanisms are unknown. These widespread monoallelic expressions have received much attention because they affect diversity in gene expression and phenotypic variation and onset of disease.

While studying dominant/recessive relationships between self-incompatibility genes, we found that the expression of recessive alleles was suppressed by small RNA derived from dominant alleles. We are now conducting studies to further clarify the mechanism of this epigenetic monoallelic expression system (Fig. 3).

References

  1. Iwano et al., Nature Plants, 1, 15128, 2015
  2. Kubo et al., Nature Plants, 1, 14005, 2015
  3. Iwano et al., Plant Cell, 26, 636-649, 2014
  4. Iwano and Takayama, Curr. Opin. Plant Biol., 15, 78-83, 2012
  5. Tarutani and Takayama, Curr. Opin. Plant Biol., 14, 608-613, 2011
  6. Kubo et al., Science, 330, 796-799, 2010
  7. Tarutani et al., Nature, 466, 983-986, 2010
  8. Tsuchimatsu et al., Nature, 464, 1342-1346, 2010
Fig.1 Mechanism for self-incompatibility in the Brassicaceae
Fig.1 Mechanism for self-incompatibility in the Brassicaceae
Fig.2 Mechanism for self-incompatibility in the Solanaceae
Fig.2 Mechanism for self-incompatibility in the Solanaceae
Fig.3 Models for epigenetic control of dominant/recessive relationship
Fig.3 Models for epigenetic control of dominant/recessive relationship
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