Research Activity
1. Quality control of membrane proteins in chloroplasts and its relationship to light adaptation
The photosynthetic apparatus is constantly damaged by photooxidation. The quality control of chloroplast proteins, which are rapidly repaired after damaged, is crucial for minimizing this photodamage. This is especially important when reaction center protein D1 in Photosystem II, which is located on thylakoid membranes is photodamaged during photosynthetic electron transfer. FtsH is a membrane-bound ATP-dependent metalloprotease and is involved in this repair cycle. We have recently shown that loss of chloroplastic homologues FtsH2 and FtsH5 in Arabidopsis reduces PSII activity upon exposure to high-intensity light and results in leaf-variegated phenotype. Although our observation demonstrates the importance of FtsH in the PSII repair cycle, the mechanism leading to leaf variegation remains unclear. We propose that the formation of variegated sectors is an adaptive response of plants to potentially lethal environmental conditions, and currently we are trying to isolate the regulatory factors by molecular genetic approaches.
2. An Arabidopsis mutant deficient in pollen mitosis
In plants, pollen has two sperm cells to perform double fertilization. Mature pollen grain has a vegetative nucleus together with the two sperm nuclei. However, another type of mature pollen grain contains only one generative nucleus. This difference in the nucleoploidity of mature pollen grains may affect pollen viability. We isolated an Arabidopsis mutant that has altered nucleoploidity. This mutant, nikaku, segregated normal tri-nuclear pollen grains and abnormal di-nuclear pollen grains at a 1:1. Our genetic analysis showed that the di-nuclear phenotype was inherited only maternally, and the transmission rate was always 1:1. These results suggest that pollen mitosis II is impaired in the mutation. Analysis of DNA content of di-nuclear pollens revealed that the mutation blocked DNA replication, suggesting that nikaku may affect pollen mitosis II at an early step.
〒710-0046 Plant Light Acclimation Research Group
Okayama University 2-20-1 Chuo, Kurashiki, Okayama 710-0046, Japan
TEL & FAX +81-86-434-1206 / E-mail: saka@rib.okayama-u.ac.jp |
