Researchers clarify main auxin biosynthesis pathway
New findings by scientists at the RIKEN Plant Science Center (PSC) have shed first-ever light on the biosynthesis pathways of a family of phytohormones known as auxins, which play a central role in plant growth and development. The findings open the door to new techniques for boosting crop yields, helping to tackle the world's pressing agricultural challenges.
Proposed IAA biosynthesis pathway
By promoting cell expansion, division and differentiation, and regulating developmental events and environmental responses, the family of plant hormones known as auxins is central to a wide variety of growth and behavioral processes in the plant's life cycle. As the most abundant and potent auxin, indole-3-acetic acid (IAA) in particular, discovered more than 70 years ago, plays a fundamental role in plant growth and development, yet surprisingly little is known about how it is synthesized.
With their latest research, published in the Proceedings of the National Academy of Sciences (PNAS), the PSC research team and the collaborators, including Yunde Zhao of University of California San Diego, sought to clarify the pathways via which this synthesis occurs. Earlier research showed that plants synthesize IAA from tryptophan, an amino acid, via a set of four such pathways, and the team's own research in 2009 indicated that IAA biosynthesis may vary among plant species. The overall picture of these pathways, however, remained unclear.
One point of contention with existing hypotheses concerns two families of enzymes named TAA (TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS) and YUC (YUCCA), each of which is required for IAA biosynthesis. While earlier research had placed these two families on distinct biosynthesis pathways, mutants deficient in TAA and YUC have very similar phenotypes, suggesting a linear relationship between the two.
Through a series of experiments on Arabidopsis using advanced mass spectroscopy techniques and enzyme assays, the research team confirmed for the first time this linear relationship. Their findings show that the TAA and YUC families are not on separate pathways, as earlier believed, but on the same pathway, with YUC catalyzing a rate-limiting step in the synthesis of IAA from indole-3-pyruvic acid (IPA). By clarifying this key step, the discovery unravels the 70-year old mystery of how auxins are synthesized and sets the groundwork for new agricultural techniques aimed at solving the world's pressing agricultural challenges.
- For more information, please contact
- Hiroyuki Kasahara
- Growth Regulation Research Group
- RIKEN Plant Science Center
- Tel: +81-(0)45-503-9660 / Fax: +81-(0)45-503-9662
- Planning Section
- Yokohama Research Promotion Division
- Tel: +81-(0)45-503-9117 / Fax: +81-(0)45-503-9113
- Global Relations Office
- RIKEN
- Tel: +81-(0)48-462-1225 / Fax: +81-(0)48-463-3687
- Mail: koho@riken.jp
Reference:
Kiyoshi Mashiguchi, Keita Tanaka, Tatsuya Sakai, Satoko Sugawara, Hiroshi Kawaide, Masahiro Natsume, Atsushi Hanada, Takashi Yaeno, Ken Shirasu, Hong Yao, Paula McSteen, Yunde Zhao, Ken-ichiro Hayashi, Yuji Kamiya, and Hiroyuki Kasahara "The main auxin biosynthesis pathway in Arabidopsis." Proceedings of the National Academy of Sciences, 2011, DOI: 10.1073/pnas.1108434108
Related press release:
UC San Diego Biologists Unravel How Plants Synthesize Their Growth Hormone
About RIKEN
RIKEN is Japan's flagship research institute devoted to basic and applied research. Over 2500 papers by RIKEN researchers are published every year in reputable scientific and technical journals, covering topics ranging across a broad spectrum of disciplines including physics, chemistry, biology, medical science and engineering. RIKEN's advanced research environment and strong emphasis on interdisciplinary collaboration has earned itself an unparalleled reputation for scientific excellence in Japan and around the world.
About the Plant Science Center
With rapid industrialization and a world population set to top 9 billion within the next 30 years, the need to increase our food production capacity is more urgent today than it ever has been before. Avoiding a global crisis demands rapid advances in plant science research to boost crop yields and ensure a reliable supply of food, energy and plant-based materials.
The RIKEN Plant Science Center (PSC), located at the RIKEN Yokohama Research Institute in Yokohama City, Japan, is at the forefront of research efforts to uncover mechanisms underlying plant metabolism, morphology and development, and apply these findings to improving plant production. With laboratories ranging in subject area from metabolomics, to functional genomics, to plant regulation and productivity, to plant evolution and adaptation, the PSC's broad scope grants it a unique position in the network of modern plant science research. In cooperation with universities, research institutes and industry, the PSC is working to ensure a stable supply of food, materials, and energy to support a growing world population and its pressing health and environmental needs.
Figure 1 IAA biosynthesis pathway proposed in the present study. The bold arrows indicate proposed functions of TAA1 and YUC, respectively.
Figure 2 Plants cannot grow normally if IAA biosynthesis by TAA and YUC gene families is disrupted (Left: normal, upper right: TAA-deficient mutant, upper right: YUC-deficient mutant).