Characterization of Arabidopsis thaliana Hydroxyphenylpyruvate Reductases in the Tyrosine Conversion Pathway.

Jing-Jing Xu,Cathie Martin,Xin Fang,Lei Yang,Chen-Yi Li,Xiao-Ya Chen,Qing Zhao

doi:10.3389/fpls.2018.01305

Abstract

Tyrosine serves as a precursor to several types of plant natural products of medicinal or nutritional interests. Hydroxyphenylpyruvate reductase (HPPR), which catalyzes the reduction of 4-hydroxyphenylpyruvic acid (pHPP) to 4-hydroxyphenyllactic acid (pHPL), has been shown to be the key enzyme in the biosynthesis of rosmarinic acid (RA) from tyrosine and, so far, HPPR activity has been reported only from the RA-accumulating plants. Here, we show that HPPR homologs are widely distributed in land plants. In Arabidopsis thaliana, which does not accumulate RA at detectable level, two homologs (HPPR2 and HPPR3) are functional in reducing pHPP. Phylogenetic analysis placed HPPR2 and HPPR3 in two separate groups within the HPPR clade, and HPPR2 and HPPR3 are distinct from HPR1, a peroxisomal hydroxypyruvate reductase (HPR). In vitro characterization of the recombinant proteins revealed that HPPR2 has both HPR and HPPR activities, whereas HPPR3 has a strong preference for pHPP, and both enzymes are localized in the cytosol. Arabidopsis mutants defective in either HPPR2 or HPPR3 contained lower amounts of pHPL and were impaired in conversion of tyrosine to pHPL. Furthermore, a loss-of-function mutation in tyrosine aminotransferase (TAT) also reduced the pHPL accumulation in plants. Our data demonstrate that in Arabidopsis HPPR2 and HPPR3, together with TAT1, constitute to a probably conserved biosynthetic pathway from tyrosine to pHPL, from which some specialized metabolites, such as RA, can be generated in specific groups of plants. Our finding may have broad implications for the origins of tyrosine-derived specialized metabolites in general.

Highlights

Tyrosine is a precursor to numerous plant natural products such as tocopherols, plastoquinone, and the specialized metabolites of dhurrin, betalains, benzylisoquinolines, and rosmarinic acid (RA), which have diverse functions in plant growth, development, and adaptation
While the 3, 4-dihydroxyphenyllactic acid part of the RA molecule is derived from tyrosine, the caffeic acid moiety comes from the general phenylpropanoid pathway via 4-coumaroylCoA, which is synthesized from phenylalanine by phenylalanine ammonia-lyase (PAL), cinnamic acid 4-hydroxylase (C4H), and 4-coumaric acid CoA-ligase (4CL) (Petersen et al, 1993)
A BLAST search of the Arabidopsis genome revealed that the predicted proteins encoded by At1g79870, At1g12550, and At2g45630 share 76, 48, and 45% identities with the hydroxyphenylpyruvate reductase (HPPR) (CAD47810.2) from Coleus blumei at the amino acid sequence level

Summary

Introduction

Tyrosine is a precursor to numerous plant natural products such as tocopherols, plastoquinone, and the specialized (or secondary) metabolites of dhurrin, betalains, benzylisoquinolines, and rosmarinic acid (RA), which have diverse functions in plant growth, development, and adaptation. Despite their substantial benefits for human health and their important functions in the physiology of plants, our understanding of the enzymes involved in tyrosine metabolism remains rudimentary. While the 3, 4-dihydroxyphenyllactic acid part of the RA molecule is derived from tyrosine, the caffeic acid moiety comes from the general phenylpropanoid pathway via 4-coumaroylCoA, which is synthesized from phenylalanine by phenylalanine ammonia-lyase (PAL), cinnamic acid 4-hydroxylase (C4H), and 4-coumaric acid CoA-ligase (4CL) (Petersen et al, 1993). It has been reported that pHPP is reduced to 4-hydroxyphenyllactic acid (pHPL) by hydroxyphenylpyruvate reductase (HPPR), which was thought to be the first step committed to RA production (Kim et al, 2004)

Methods

Results

Conclusion