Biosynthesis and Metabolism of Garlic Odor Compounds in Cultivated Chinese Chives (Allium tuberosum) and Wild Chinese Chives (Allium hookeri)

Abstract

Chinese chives is a popular herb vegetable and medicine in Asian countries. Southwest China is one of the centers of origin, and the mountainous areas in this region are rich in wild germplasm. In this study, we collected four samples of germplasm from different altitudes: a land race of cultivated Chinese chives (Allium tuberosum), wide-leaf chives and extra-wide-leaf chives (Allium hookeri), and ovoid-leaf chives (Allium funckiaefolium). Leaf metabolites were detected and compared between A. tuberosum and A. hookeri. A total of 158 differentially accumulated metabolites (DAM) were identified by Gas Chromatography—Mass Spectrometry (GC-MS) and Liquid Chromatography—Mass Spectrometry (LC-MS), among which there was a wide range of garlic odor compounds, free amino acids, and sugars. A. hookeri contains a higher content of fructose, garlic odor compounds, and amino acids than A. tuberosum, which is supported by the higher expression level of biosynthetic genes revealed by transcriptome analysis. A. hookeri accumulates the same garlic odor compound precursors that A. tuberosum does (mainly methiin and alliin). We isolated full-length gene sequences of phytochelatin synthase (PCS), γ-glutamyltranspeptidases (GGT), flavin-containing monooxygenase (FMO), and alliinase (ALN). These sequences showed closer relations in phylogenetic analysis between A. hookeri and A. tuberosum (with sequence identities ranging from 86% to 90%) than with Allium cepa or Allium sativum (which had a lower sequence identity ranging from 76% to 88%). Among these assayed genes, ALN, the critical gene controlling the conversion of odorless precursors into odor compounds, was undetected in leaves, bulbs, and roots of A. tuberosum, which could account for its weaker garlic smell. Moreover, we identified a distinct FMO1 gene in extra-wide-leaf A. hookeri that is due to a CDS-deletion and frameshift mutation. These results above reveal the molecular and metabolomic basis of impressive strong odor in wild Chinese chives.

Phenolic Content, Amino Acids, Volatile Compounds, Antioxidant Capacity, and Their Relationship in Wild Garlic (A. ursinum L.)

“…Thiosulfinates are also highly reactive and, as such, undergo further spontaneous reactions, giving rise to acyclic sulfides, dithiines, thiolanes, and ajoenes [4,31]. Our results regarding the correlation between amino acids and VOCs are in line with those of several authors who have proposed a pathway for the biosynthesis of CSOs, since our results show how the content of amino acids involved in the pathway is inversely proportional to the content of VOCs [4,7,18,[36][37][38][39][40][41][42][43][44]. In addition to the glutathione precursor, volatile sulfur compounds can be synthetized from sulfur-containing amino acids, such as methionine.…”

Targeted Metabolome Profiling of Indonesian Shallots and Japanese Long-Day/Short-Day Bulb Onions

“…This hypothesis is also supported by recent study on flavin-dependent S-oxygenase (FMO), which preferably utilizes S-allyl-L-cysteine, rather than γ-glutamyl-S-allyl-L-cysteine, as the substrate [18,19]. One plausible pathway for the biosynthesis of ACSO involves biosynthesis of S-2-carboxypropyl glutathione from glutathione and methacrylic acid [18,40]. Whereas another rout involves the biosynthesis of S-2-carboxypropyl glutathione from γ-glutamyl cysteine without passing through glutathione (Figure 6).…”

“…In turn, cysteine acts as a precursor or donor of reduced-S for a range of S-compound biosynthesis [39]. Today, the biosynthetic pathway of ACSO has become much clearer despite some of its details remain under debate [40]. Early studies by Lancaster and Shaw [41] and Randle et al [42] have proposed a putative pathway via glutathione S-conjugates based on pulse radiolabeling studies of Allium tissues.…”

Integrating Microbial Fuel Cell and Hydroponic Technologies Using a Ceramic Membrane Separator to Develop an Energy–Water–Food Supply System

“…A. tuberosum is a tough, fibrous, and edible perennial plant. It is easy to grow in different conditions, and it can adapt to various environments [ 19 ]. A. tuberosum has been widely cultivated for its culinary value in East Asia (e.g., China, Korea, Japan), Southeast Asia, and Northeast India [ 20 ].…”