The synthesis of small organic molecules, known as specialized or secondary metabolites, is one mechanism by which plants resist and tolerate biotic and abiotic stress. Many specialized metabolites are derived from the aromatic amino acids phenylalanine (Phe) and tyrosine (Tyr). In addition, the improved characterization of compounds derived from these amino acids could inform strategies for developing crops with greater resilience and improved traits for the biorefinery. Sorghum and other grasses possess phenylalanine ammonia-lyase (PAL) enzymes that generate cinnamic acid from Phe and bifunctional phenylalanine/tyrosine ammonia-lyase (PTAL) enzymes that generate cinnamic acid and p-coumaric acid from Phe and Tyr, respectively. Cinnamic acid can, in turn, be converted into p-coumaric acid by cinnamate 4-hydroxylase. Thus, Phe and Tyr are both precursors of common downstream products. Not all derivatives of Phe and Tyr are shared, however, and each can act as a precursor for unique metabolites. In this study, ¹³C isotopic-labeled precursors and the recently developed Precursor of Origin Determination in Untargeted Metabolomics (PODIUM) mass spectrometry (MS) analytical pipeline were used to identify over 600 MS features derived from Phe and Tyr in sorghum. These features comprised 20% of the MS signal collected by reverse-phase chromatography and detected through negative-ionization. Ninety percent of the labeled mass features were derived from both Phe and Tyr, although the proportional contribution of each precursor varied. In addition, the relative incorporation of Phe and Tyr varied between metabolites and tissues, suggesting the existence of multiple pools of p-coumaric acid that are fed by the two amino acids. Furthermore, Phe incorporation was greater for many known hydroxycinnamate esters and flavonoid glycosides. In contrast, mass features derived exclusively from Tyr were the most abundant in every tissue. The Phe- and Tyr-derived metabolite library was also utilized to retrospectively annotate soluble MS features in two brown midrib mutants (bmr6 and bmr12) identifying several MS features that change significantly in each mutant.

有机小分子（称为特化或次生代谢物）的合成是植物抵抗和耐受生物和非生物胁迫的一种机制。许多特殊的代谢物来源于芳香族氨基酸苯丙氨酸 (Phe) 和酪氨酸 (Tyr)。此外，对源自这些氨基酸的化合物的改进表征可以为开发具有更大弹性和改善生物精炼特性的作物的策略提供信息。高粱和其他草类具有苯丙氨酸解氨酶 (PAL) 酶，可从 Phe 生成肉桂酸，以及双功能苯丙氨酸/酪氨酸解氨酶 (PTAL) 酶，可生成肉桂酸和磷-分别来自 Phe 和 Tyr 的香豆酸。反过来，肉桂酸可以转化为磷- 肉桂酸 4-羟化酶产生香豆酸。因此，Phe 和 Tyr 都是常见下游产品的前体。然而，并非 Phe 和 Tyr 的所有衍生物都是共享的，并且每种衍生物都可以作为独特代谢物的前体。在本研究中，¹³使用 C 同位素标记的前体和最近开发的非靶向代谢组学 (PODIUM) 质谱 (MS) 分析管道中的来源测定前体来识别来自高粱中 Phe 和 Tyr 的 600 多个 MS 特征。这些特征包括由反相色谱收集并通过负电离检测的 MS 信号的 20%。尽管每种前体的比例贡献各不相同，但 90% 的标记质量特征均来自 Phe 和 Tyr。此外，Phe 和 Tyr 的相对掺入在代谢物和组织之间有所不同，表明存在多个池磷-由两种氨基酸供给的香豆酸。此外，许多已知的羟基肉桂酸酯和类黄酮糖苷的 Phe 掺入量更大。相比之下，完全源自 Tyr 的质量特征在每种组织中最为丰富。还利用 Phe 和 Tyr 衍生的代谢物库对两种可溶性 MS 特征进行回顾性注释。棕色中脉 突变体（bmr6 和 bmr12) 识别在每个突变体中发生显着变化的几个 MS 特征。