TAT1 and TAT2 tyrosine aminotransferases have both distinct and shared functions in tyrosine metabolism and degradation in Arabidopsis thaliana

Authors: WANG, MINMIN - University Of Wisconsin; TODA, KYOKO - University Of Wisconsin; Block, Anna; MAEDA, HIROSHI - University Of Wisconsin

Submitted to: Journal of Biological Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/9/2019
Publication Date: 3/8/2019
Citation: Wang, M., Toda, K., Block, A.K., Maeda, H.A. 2019. TAT1 and TAT2 tyrosine aminotransferases have both distinct and shared functions in tyrosine metabolism and degradation in Arabidopsis thaliana. Journal of Biological Chemistry. 294(10):3563-3576. https://doi.org/10.1074/jbc.RA118.006539.
DOI: https://doi.org/10.1074/jbc.RA118.006539

Interpretive Summary: The amino acid tyrosine is an important compound in plants as it serves as a building block for protein synthesis. Tyrosine is also used to make antioxidants called tocopherols and in cases where production of sugar from photosynthesis is insufficient, it can be used by the plants as an alternative energy source. The model plant Arabidopsis (Thale cress) has two genes that encode for tyrosine aminotransferases (TATs). In this study a scientist from USDA-ARS, Gainesville, FL in collaboration with researchers from the University of Wisconsin Madison show that one TAT (TAT1) is more important than the other (TAT2) for making tocopherols and using tyrosine as an energy source. This finding means that breeding or engineering efforts targeting this gene in crop species could potentially enhance both the level of these important antioxidants and make plants that are more able to resist conditions of limited sugar availability.

Technical Abstract: Plants produce various L-tyrosine (Tyr)-derived compounds that are critical for plant adaptation, and also have pharmaceutical or nutritional importance in human health. Tyrosine aminotransferases (TATs) catalyze the reversible transamination between Tyr and 4-hydroxyphenylpyruvate (HPP), which is the entry reaction of both biosynthesis of various natural products and degradation of Tyr for recycling of energy and nutrients in plants. To understand how Tyr is metabolized in plants, this study investigated the in vivo roles of TAT1 (At5g53970) and TAT2 (At5g36160) in the model plant Arabidopsis thaliana. The tat1 mutants of Arabidopsis showed elevated and decreased levels of Tyr and tocopherols, respectively, as previously reported. The tat2 mutation had no effects by itself but, together with tat1, had additive effects on the Tyr accumulation, and the decreased level of tocopherols under high light stress. tat1 showed vulnerability upon continuous dark treatment associated with early drop in respiratory activity and depletion of sucrose, relative to wild-type and tat2. During isotope-labeled Tyr feeding in the dark, tat1 exhibited much slower 13C incorporation than wild-type and tat2 into tocopherols as well as fumarate and other the tricarboxylic acid (TCA) cycle intermediates. These results demonstrate that TAT1 and to a lesser extent TAT2 function together in tocopherol biosynthesis, while TAT1 plays the major role in degradation of Tyr in planta.