Masatake Kanai

By Masatake Kanai, Shoji Mano, Makoto Hayashi and Mikio Nishimura

Seeds are storage organ in plants and main resource of plant oils to human civilization and the demand of plant oils are increasing yearly and expansion of the production capacity is an urgent issue worldwide. Thus, it is necessary to improve oil yields per unit area and generation of crops with high-oil content is needed. Arabidopsis thaliana plays a vital role in advancement of genetics and molecular biology in plant sciences. The forward and reverse genetic approaches with Arabidopsis have provided an overview of triacylglycerol metabolism. The elucidation of the overview contributes to understanding of spatiotemporal regulation of a metabolic flow of triacylglycerol metabolism in plant cell. This understanding sheds light on bottlenecks in triacylglycerol biosynthesis and provides novel clues for increasing seed triacylglycerol content. Recent advance in metabolic engineering approaches demonstrate several evidences that triacylglycerol metabolism is coordinated with other metabolisms. Most notably, triacylglycerol biosynthesis competes with biosynthesis of starch or seed storage proteins. These studies indicate that alterations of the metabolic pathways to avoid the competitions could be a novel concept for increasing seed oil content.

Part of the book: New Challenges in Seed Biology

By Shoji Mano, Kazumi Hikino and Masatake Kanai

Peroxisomes are ubiquitous organelles present in most eukaryotic cells that have important biological functions related to fatty acid metabolism and detoxification of reactive oxygen species. Disruption of peroxisomal function affects the survival of cells and organisms. Peroxisomes do not have their own genome, and peroxisomal proteins are encoded in the nuclear genome. Therefore, efficient and accurate posttranslational transport of peroxisomal proteins is necessary to maintain peroxisomal function. In mammals, yeast, and plants, many factors involved in protein transport to peroxisomes have been identified and their molecular mechanisms elucidated. In plants, analysis of Arabidopsis peroxisome mutants, such as apem (aberrant peroxisome morphology) and ibr (indole-3-butyric acid-response), enabled the identification of the factors mediating protein transport. Of these, several proteins, such as PEX1 (Peroxin 1), PEX2, PEX4, PEX6, PEX10, PEX12, PEX22, and APEM9, constitute the ubiquitin system on the peroxisomal membrane, and loss of function of each protein reduces the efficiency of protein transport to peroxisomes. This ubiquitin-dependent peroxisomal protein transport system is also present in yeast and mammalian cells and is an example of a type of ubiquitin modification that serves as a signaling tag rather than as a tag for protein degradation. This chapter introduces the factors involved in protein transport to the peroxisome via the ubiquitin system in plants and outlines their functions.

Part of the book: Modifications in Biomacromolecules