Phenylpyruvate Contributes to the Synthesis of Fragrant Benzenoid–Phenylpropanoids in Petunia × hybrida Flowers

Abstract

Phenylalanine (Phe) is a precursor for a large group of plant specialized metabolites, including the fragrant volatile benzenoid–phenylpropanoids (BPs). In plants, the main pathway leading to production of Phe is via arogenate, while the pathway via phenylpyruvate (PPY) is considered merely an alternative route. Unlike plants, in most microorganisms the only pathway leading to the synthesis of Phe is via PPY. Here we studied the effect of increased PPY production in petunia on the formation of BPs volatiles and other specialized metabolites originating from Phe both in flowers and leaves. Stimulation of the pathway via PPY was achieved by transforming petunia with PheA∗, a gene encoding a bacterial feedback insensitive bi-functional chorismate mutase/prephenate dehydratase enzyme. PheA∗ overexpression caused dramatic increase in the levels of flower BP volatiles such as phenylacetaldehyde, benzaldehyde, benzyl acetate, vanillin, and eugenol. All three BP pathways characterized in petunia flowers were stimulated in PheA∗ flowers. In contrast, PheA∗ overexpression had only a minor effect on the levels of amino acids and non-volatile metabolites both in the leaves and flowers. The one exception is a dramatic increase in the level of rosmarinate, a conjugate between Phe-derived caffeate and Tyr-derived 3,4-dihydroxyphenylacetate, in PheA∗ leaves. PheA∗ petunia flowers may serve as an excellent system for revealing the role of PPY in the production of BPs, including possible routes directly converting PPY to the fragrant volatiles. This study emphasizes the potential of the PPY route in achieving fragrance enhancement in flowering plants.

Increased substrate availability reveals the potential of scentless lisianthus flowers in producing fragrant benzenoid‐phenylpropanoids

“…Both in the petals and leaves, there was no increase in the concentration of these compounds from the PAAS pathway in the transformed lines increasing production of Phe. In addition, feeding detached petals or leaves with benzyl alcohol had no significant effect on these two metabolites (Figure 1), as expected, due to their metabolic divergence (Gonda et al, 2018;Oliva et al, 2017;Qualley et al, 2012).…”

“…The vial was sealed and stored at room temperature (12-48 h) to reach equilibrium of the gas phase. Solid-phase microextraction (SPME) sampling was conducted according to Oliva et al (2017). The volatile reaction products were analyzed on GC-MS 7890 (Agilent) using the solid-phase micro extraction (SPME) method as described in Davidovich-Rikanati et al (2008).…”

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

“…The reason for its inability to be converted to phenylalanine is currently unknown but could be due to a plastidial localization of this phenylpyruvate pool, where it is inaccessible to the cytosolic PhPPY-AT. We do not exclude that under shikimate feeding, as well as under overexpression of a bacterial CM/PDT in Arabidopsis and petunia plastids 14,15 , phenylpyruvate could be converted to phenylalanine in plastids by unknown aminotransferase(s) with low affinity towards phenylpyruvate or by moonlight activities of some aminotransferase(s). Nevertheless, this activity was unable to bypass the blockage in the cytosolic pathway in PhCM2 -RNAi flowers and recover phenylalanine levels (Supplementary Figure 7).…”

“…Most microorganisms use the phenylpyruvate pathway to synthesize phenylalanine, but knowledge about this route in plants is still very fragmented 1,13 . The contribution of phenylpyruvate to phenylalanine biosynthesis has been demonstrated in Arabidopsis and petunia expressing a bacterial bifunctional chorismate mutase/prephenate dehydratase (CM/PDT) in plastids 14,15 . However, to date, no genes involved in this route have been identified in plants, except for a phenylpyruvate aminotransferase (PPY-AT) preferentially converting phenylpyruvate to phenylalanine 16 .…”

Biotechnological improvement of ornamental plants

“…Considering the last five years, scientific literature include transgenic petunia events obtained to study floral pigmentation (BOASE et al, 2015;CHU et al, 2015;AI et al, 2016;SHAIPULAH et al, 2015), biotic (WANG et al, 2013a;GARGUL et al, 2015;SUN et al, 2016) and abiotic stress (ESTRADA-MELO et al, 2015), selfincompatibility (LI et al, 2014;KUBO et al, 2016), adventitious root formation (LISCHWESKI et al, 2015), floral development (MOREL et al, 2017;O'DONOGHUE et al, 2017;YUE et al, 2017), plant architecture (LIANG et al, 2014;GARGUL et al, 2015), flower senescence (WANG et al, 2013a;WANG et al, 2013b;YIN et al, 2015), floral volatiles (CNA'ANI et al, 2015;SHAIPULAH et al, 2015;ADEBESIN et al, 2017;OLIVA et al, 2017), herbivore defence (KESSLER et al, 2013;SASSE et al, 2016), and others.…”