Abstract
Eucommia ulmoides Oliver is widely distributed in China. This species has been used mainly in medicine due to the high concentration of chlorogenic acid (CGA), flavonoids, lignans, and other compounds in the leaves and barks. However, the categories of metabolites, dynamic changes in metabolite accumulation and overall molecular mechanisms involved in metabolite biosynthesis during E. ulmoides leaf growth and development remain unknown. Here, a total of 515 analytes, including 127 flavonoids, 46 organic acids, 44 amino acid derivatives, 9 phenolamides, and 16 vitamins, were identified from four E. ulmoides samples using ultraperformance liquid chromatography–mass spectrometry (UPLC-MS) (for widely targeted metabolites). The accumulation of most flavonoids peaked in growing leaves, followed by old leaves. UPLC-MS analysis indicated that CGA accumulation increased steadily to a high concentration during leaf growth and development, and rutin showed a high accumulation level in leaf buds and growing leaves. Based on single-molecule long-read sequencing technology, 69,020 transcripts and 2880 novel loci were identified in E. ulmoides. Expression analysis indicated that isoforms in the flavonoid biosynthetic pathway and flavonoid metabolic pathway were highly expressed in growing leaves and old leaves. Co-expression network analysis suggested a potential direct link between the flavonoid and phenylpropanoid biosynthetic pathways via the regulation of transcription factors, including MYB (v-myb avian myeloblastosis viral oncogene homolog) and bHLH (basic/helix-loop-helix). Our study predicts dynamic metabolic models during leaf growth and development and will support further molecular biological studies of metabolite biosynthesis in E. ulmoides. In addition, our results significantly improve the annotation of the E. ulmoides genome.
Highlights
Eucommia ulmoides Oliver is the only species in the family Eucommiaceae and is widely distributed in China [1,2]
Our findings provide new insights into the molecular mechanisms associated with the biosynthesis and regulation of flavonoids and phenylpropanoids during E. ulmoides leaf growth and development and highlight the usefulness of an integrated approach for understanding this process
E. ulmoides leaves developed from the leaf primordium, which is located around the growing point of the leaf bud (Figure 1B)
Summary
Eucommia ulmoides Oliver is the only species in the family Eucommiaceae and is widely distributed in China [1,2]. The pharmacology and efficacy of E. ulmoides have been well documented in ancient Chinese medicinal books such as Shennong’s Classic of Materia Medica and Compendium of Materia Medica. This species is an important source of natural rubber [4,5]. E. ulmoides has important applications in landscaping and soil and water conservation [3]. Due to its many economic, ecological and social benefits, E. ulmoides is one of the most important forest resources in China
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