Study of molecular mechanisms involved in fructan metabolism in onion bulbs

2020 Fiscal Year Final Research Report

• Project/Area Number: 17H03760
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Horticultural science
• Research Institution: Hokkaido University
• Principal Investigator: Shimura Hanako 北海道大学, 農学研究院, 講師 (20507230)
• Co-Investigator(Kenkyū-buntansha): 上野 敬司 酪農学園大学, 農食環境学群, 准教授 (90441964) ; 前田 智雄 弘前大学, 農学生命科学部, 教授 (90530478)
• Project Period (FY): 2017-04-01 – 2020-03-31
• Keywords: タマネギ / フルクトオリゴ糖 / フルクタン分解酵素

Outline of Final Research Achievements

This study aimed to elucidate molecular mechanisms involved in the differences of fructan accumulation in the harvested bulbs in two onion cultivars. From planting to harvest, the fructan contents of bulbs and leaf blades and the enzyme activities related to fructan metabolism were examined. We found that the difference in enzymatic activities of fructan hydrolase (FEH), not fructosyltransferases, and sucrose accumulation before bulb enlargement would be related to the levels of fructan accumulation in the bulb. There have been no reports of the FEH gene in onion, but in this study, we successfully identified a FEH showing 6G & 1-FEH activity. All fructan hydrolases known in plants showed amino acid similarity to cell-wall invertases, but we identified a FEH that is homologous to vacuolar invertases for the first time. In this study, we experimentally demonstrated that the enzymes involved in fructan synthesis and degradation are actually localized in the vacuole.

Free Research Field

園芸学、植物生理学

Academic Significance and Societal Importance of the Research Achievements

今までに植物で同定されたフルクタン合成酵素は、液胞型インベルターゼとのアミノ酸相同性を示すことから液胞に局在すると考えられてきた。一方、フルクタン加水分解酵素はすべて細胞壁型インベルターゼに相同性を示し、フルクタン代謝酵素の細胞内局在については議論が続いていた。本研究では、液胞型インベルターゼとの相同性を示すフルクタン加水分解酵素を植物で初めて同定した。また、これまでフルクタン代謝酵素の細胞内局在を示す研究例はなかったが、本研究では、フルクタン合成および分解に関わる酵素がどちらも液胞に局在することを実験的に証明することができた。