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

Abstract

Edited by F. Peter Guengerich Plants produce various L-tyrosine (Tyr)-derived compounds that are critical for plant adaptation and have pharmaceutical or nutritional importance for human health. Tyrosine aminotransferases (TATs) catalyze the reversible reaction between Tyr and 4-hydroxyphenylpyruvate (HPP), representing the entry point in plants for both biosynthesis of various natural products and Tyr degradation in the recycling of energy and nutrients. To better understand the roles of TATs and how Tyr is metabolized in planta, here we characterized single and double loss-of-function mutants of TAT1 (At5g53970) and TAT2 (At5g36160) in the model plant Arabidopsis thaliana. As reported previously, tat1 mutants exhibited elevated and decreased levels of Tyr and tocopherols, respectively. The tat2 mutation alone had no impact on Tyr and tocopherol levels, but a tat1 tat2 double mutant had increased Tyr accumulation and decreased tocopherol levels under highlight stress compared with the tat1 mutant. Relative to WT and the tat2 mutant, the tat1 mutant displayed increased vulnerability to continuous dark treatment, associated with an early drop in respiratory activity and sucrose depletion. During isotope-labeled Tyr feeding in the dark, we observed that the tat1 mutant exhibits much slower 13 C incorporation into tocopherols, fumarate, and other tricarboxylic acid (TCA) cycle intermediates than WT and the tat2 mutant. These results indicate that TAT1 and TAT2 function together in tocopherol biosynthesis, with TAT2 having a lesser role, and that TAT1 plays the major role in Tyr degradation in planta. Our study also highlights the importance of Tyr degradation under carbon starvation conditions during dark-induced senescence in plants.

A Role for Tocopherol Biosynthesis in Arabidopsis Basal Immunity to Bacterial Infection

“…To a similar extent, TAT1 is involved in basal tocopherol production in unstressed leaves ( Fig. 5B; Riewe et al, 2012;Wang et al, 2019). Sequence comparisons suggest that Arabidopsis possesses nine TAT1 homologs (Wang et al, 2016), some of which might code for Tyr aminotransferases that further contribute to basal and inducible tocopherol biosynthesis.…”

“…We also analyzed tat1-2 mutant plants (SALK_141402), which harbor a T-DNA insertion in the Tyr aminotransferase gene TAT1 and exhibit reduced basal tocopherol levels (Wang et al, 2019). Consistently, tat1-2 showed less than half of the levels of aand b-tocopherol than the Col-0 wild type in mock-control plants.…”

“…L-Tyr is first deaminated to p-hydroxyphenylpyruvate (HPP) by Tyr aminotransferase. In Arabidopsis, TYROSINE AMINO-TRANSFERASE1 (TAT1) takes over a significant portion of this transamination reaction (Riewe et al, 2012;Wang et al, 2019). In a second step, HPP is oxygenated to HGA by p-hydroxyphenylpyruvate dioxygenase (HPPD; DellaPenna and Pogson, 2006).…”

Role of Cytosolic, Tyrosine-Insensitive Prephenate Dehydrogenase inMedicago truncatula

“…1 ) and the gene encoding HPP dioxygenase (HPPD, (Siehl et al, 2014), a senescence-activated enzyme involved in Tyr catabolism ( Supplementary Fig. 5a )(Wang et al, 2019). To experimentally test the potential involvement of PDH in senescence, PDH gene expression and enzymatic activity were monitored at different developmental stages during natural leaf senescence ( Supplementary Fig.…”

“…To further examine Tyr catabolism during leaf senescence under artificial, but controlled, conditions excised leaves from Wt and mutants were exposed to an extended dark treatment (Xing and Last, 2017; Wang et al, 2019). Over 7 days, leaves from Wt and mutants responded to dark-induced senescence similarly with no apparent growth phenotypes ( Supplementary Fig.…”