Identification of genes involved in the synthesis of tannins that detoxify aluminum in Eucalyptus camaldulensis

Identification of UDP glucosyltransferases from the aluminum-resistant tree Eucalyptus camaldulensis forming β-glucogallin, the precursor of hydrolyzable tannins

Ko Tahara (a&b), Mitsuru Nishiguchi (b), Andrej Frolov (c), Juliane Mittasch (a), Carsten Mikowski (a)

(a) Martin Luther University Halle-Wittenberg, Halle, Germany.
(b) Department of Forest Molecular Genetics and Biotechnologies, FFPRI, Tsukuba, Ibaraki, Japan.

(c) Leibniz Institute of Plant Biochemistry, Halle, Germany.

Phytochemistry, 152:154-161, August 2018, DOI: 10.1016/j.phytochem.2018.05.005( External link )

The tree Eucalyptus camaldulensis is native to Australia; it is highly resistant to excessive aluminum toxicity. Aluminum toxicity has been a major issue in acidic soils, which cover 30% of the world’s land area. Tannins^note1) synthesized in the roots of E. camaldulensis can neutralize aluminum toxicity by binding to aluminum entering the roots; therefore, it might be possible to produce trees that are resistant to excessive aluminum toxicity by controlling the amount of tannins present in the trees. To control the production and amount of tannins, it is necessary to determine how trees synthesize them.

β-glucogallin is an important molecule that serves as the precursor for tannin biosynthesis; it is used as a substrate when tannins are synthesized in E. camaldulensis. Here, the enzymes^note2) for β-glucogallin synthesis present in E. camaldulensis were identified for the first time. E. camaldulensis contains at least four isozymes, and we have successfully isolated the genes that code for these isozymes. These isozymes are believed to supply β-glucogallin required for tannin synthesis.

In the future, we will work to determine how tannins are synthesized from β-glucogallin in E. camaldulensis. By elucidating the entire tannin biosynthetic pathway, we believe that it will be possible to produce trees resistant to aluminum toxicity and help contribute to reforestation of devastated acidic land.

^Note1 Tannin: A type of polyphenol present in plants.

^Note2 Enzyme: A protein that works as a catalyst in chemical reactions in living organisms.

Figure 1. Eucalyptus camaldulensis can grow well in acidic soils where aluminum toxicity is a problem

Figure 2. Enzymes synthesizing β-glucogallin were identified in Eucalyptus camaldulensis. The aluminum detoxifying tannin oenothein B is synthesized using β-glucogallin as the substrate.

Pictures and Figures were created by modifying the graphical abstract of the article published by Elsevier with permission from Elsevier.

https://www.sciencedirect.com/journal/phytochemistry( External link )