Faculty and research guide

Laboratory of Molecular Breeding

Reiko Motohashi

Research content
Theme 1: Studying the chloroplast proteins using the Arabidopsis tag lines
  Photosynthesis is a function of plants that is extremely important to the environment. Through photosynthesis, plants supply the oxygen that is indispensable for nearly all life on earth. The photosynthesis takes place in the chloroplast. Chloroplasts are also where substances such as vitamins and plant hormones are produced. Although chloroplasts have important functions, but they have their own transcription-translation organization independent of the cell nucleus, and yet they are in control of the nucleus. Although about 80 genes are encoded in the chloroplast genome of Arabidopsis, most of the protein that constitutes the chloroplast is encoded in the nuclear genome. Among the chloroplast proteins, a functional analysis has been made of about 2,300 nuclear codes of chloroplast proteins. These functions can be inferred from homology with cyanobacterium or other living things. However, the functional analysis of chloroplast proteins that do not share homology with other living things (whose functions are considered to be unique to the higher plant) has not progressed very far. We collect knock-out lines of nuclear-encoded chloroplast proteins, and identify the genes that are involved in wide range of chloroplast functions, such as photosynthesis, light response, and metabolite production.

How our research contributes :
It is important to improve plant productivity, as one means of addressing the big issues that strongly affect the foundations of our lives, such as global warming and the rapid destruction of the environment. To enhance plant productivity, it is important to strengthen plant’s capacity to fix carbon dioxide with higher efficiency, accumulate nutrients, to strengthen their resistance to pathogens and their tolerance for environmental stress, such as salt, strong light, drought, and high temperature. In the course of our research, we have clarified the functions of the nuclear-encoded genes, whose functions were previously unknown. We found that they are involved in many aspects of photosynthesis and chloroplast development, and in the production of various substances. One of our discoveries comes from screening a mutant that has a problem with its chloroplast function. By over-expressing those genes involved we identify their role in chloroplast development, photosynthesis, and the production of substances. Such approach can produce a new high-functioning plant with augmented functions that can be selected in advance. Therefore, plants may be created that can grow even in a harsh environment, and other plants may be developed with improved carbon dioxide fixation. These would allow the area under cultivation to be expanded and lead to solving the problems of insufficient food supplies and global warming.

Theme 2: Clarification of the chromoplast differentiation mechanism using tomato fruit
Plastids, including chloroplasts, are altered to achieve different types of morphology, according to the cells need. In terms of morphology, chloroplasts change into leaves, amyloplasts change into roots, and chromoplasts into fruit. By using the rapidly developing proteome analysis and tomato genomic resources, large numbers of proteins specific to chromoplasts in tomatoes can be identified. We are particularly interested in conducting a comprehensive analysis of the proteins involved in the differentiation of proplastids and chloroplasts during fruit maturation into chromoplasts, to identify the key proteins involved in chromoplast differentiation, and to learn to control that function.
We examine proteome, transcriptome and plastid changes over four distinct developmental stages of ‘Micro-Tom’ fruit. Additionally, to discover more about the relationship between fruit color and plastid differentiation, we also analyze and compare ‘Micro-Tom’ results with those from various color tomatoes. We postulate from plastid proteomic data that some proteins have a role in carotenoid accumulation and chromoplast differentiation. We observe these phenotypes of transgenic plants having gene silencing or over expression of genes related to carotenoid accumulation and chromoplast differentiation.

Theme 3: Making larger seeds to increase oil production in Jatropha curcas L.
Biofuel can provide a way to deal with the high demand of fuel, since biofuel is renewable. Jatropha curcas L. is a plant which can produce biofuel and is of interest to many researchers and manufacturers because of its seeds high oil-rich characteristic. We find some candidate genes that produce increased seed size in other plants by using over-expressing system. We transfer these genes into Jatropha to make larger seeds.

Laboratory members
Professor Reiko Motohashi: Analysis of plastid functions and differentiation mechanisms using Arabidopsis and tomatoes

Technical personnel: Chikako Fukazawa