Completion of the cytosolic post-chorismate phenylalanine biosynthetic pathway in plants

Abstract

In addition to being a vital component of proteins, phenylalanine is also a precursor of numerous aromatic primary and secondary metabolites with broad physiological functions. In plants phenylalanine is synthesized predominantly via the arogenate pathway in plastids. Here, we describe the structure, molecular players and subcellular localization of a microbial-like phenylpyruvate pathway for phenylalanine biosynthesis in plants. Using a reverse genetic approach and metabolic flux analysis, we provide evidence that the cytosolic chorismate mutase is responsible for directing carbon flux towards cytosolic phenylalanine production via the phenylpyruvate pathway. We also show that an alternative transcription start site of a known plastidial enzyme produces a functional cytosolic prephenate dehydratase that catalyzes the conversion of prephenate to phenylpyruvate, the intermediate step between chorismate mutase and phenylpyruvate aminotransferase. Thus, our results complete elucidation of phenylalanine biosynthesis via phenylpyruvate in plants, showing that this pathway splits from the known plastidial arogenate pathway at chorismate, instead of prephenate as previously thought, and the complete pathway is localized in the cytosol.

Arabidopsis MYB4 plays dual roles in flavonoid biosynthesis

“…However, the phenylalanine level in ref4‐3 mutant plants was slightly increased compared with that in wild‐type plants, and knocking‐out MYB4 , MYB7 and MYB32 in both wild‐type plants and the ref4‐3 background mutant had almost no impact on the levels of phenylalanine (Figure S6), indicating that the free form of phenylalanine is not only determined by the biosynthesis but also the biosynthesis of downstream metabolites of which phenylalanine serves as a precursor. Recently, it was reported that Arabidopsis ADT6 may contain two alternative open reading frames and could encode a cytosolic enzyme, as with the petunia counterpart (Qian et al , ). The fact that MYB4 directly controls the expression of ADT6 suggests that flavonoid biosynthesis may partially derive from the cytosolic pool of phenylalanine.…”

“…The fact that MYB4 directly controls the expression of ADT6 suggests that flavonoid biosynthesis may partially derive from the cytosolic pool of phenylalanine. To further investigate this possibility, we used the same two pairs of primers that were published to distinguish the two isoforms (Qian et al , ). Our data indicated that the transcript of the short isoform is much more abundant than that of the longer one, as previously reported (Figure S7a,b).…”

Location, location! cellular relocalization primes specialized metabolic diversification

“…Along with the loss of its native substrate, arogenate, cytosolic ADT gained access to the alternative substrate prephenate in the cytosol. Despite ~ 10‐fold preference for arogenate over the non‐native substrate, prephenate , ADT promiscuously converts prephenate into phenylpyruvate; this is further converted into Phe‐derived phenylacetaldehyde, a floral scent component involved in pollinator attraction . ADT is more highly expressed at night than during the day, consistent with diurnally regulated Phe‐derived volatile emission in petunia .…”

“…). A single petunia ADT gene produces both a cytosolic and plastidic ADT, via alternative transcription start sites . Along with the loss of its native substrate, arogenate, cytosolic ADT gained access to the alternative substrate prephenate in the cytosol.…”

Role of Cytosolic, Tyrosine-Insensitive Prephenate Dehydrogenase inMedicago truncatula

“…1 ) (D’Amato et al, 1984; Eberhard et al, 1996; Ding et al, 2007; Schenck et al, 2015; Wang et al, 2016). Also, a cytosolic Phe pathway was recently identified in plants (Yoo et al, 2013; Qian et al, 2019). Hypothesis II: PDH is involved in the production of Tyr or HPP-derived metabolite(s) (Fig.…”