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<p>Sesquiterpenes and triterpenes are the primary contributors to the bitterness of stem lettuce (<i>Lactuca sativa var. augustana</i>), with significant bitterness variations observed among varieties with different leaf colors. To investigate the formation mechanisms of bitter compounds, two stem lettuce genotypes green-leaf (WS01) and purple-leaf (WS06) were used as experimental materials. By integrating metabolomic and transcriptomic analyses, we systematically compared the regulatory characteristics of terpenoid biosynthesis at the commercial harvest stage and the bolting stage. UPLC-MS/MS-based metabolomic profiling identified 33 terpenoid compounds, including 22 sesquiterpenes and 11 triterpenes. Among these, the sesquiterpene lactone lactucopicrin was the most abundant, accounting for approximately 60% of the total terpenoid content. Comparative analysis revealed higher total terpenoid content in the purple-leaf genotype. However, the green-leaf genotype accumulated more sesquiterpenes at the commercial harvest stage, while this trend reversed at the bolting stage. In contrast, triterpenes exhibited an opposite accumulation pattern, suggesting potential metabolic competition or antagonistic regulation between sesquiterpene and triterpene biosynthesis during development. Transcriptomic analysis identified 33,498 differentially expressed genes, including 2,387 novel genes. Enrichment analysis revealed that 18 terpenoid biosynthesis-related genes were significantly enriched in the "Sesquiterpenoid and triterpenoid biosynthesis" pathway (ko00909), displaying genotype- and stage-specific expression patterns. These genes were predominantly upregulated in the green-leaf genotype at the commercial harvest stage and in the purple-leaf genotype at the bolting stage, indicating spatiotemporal differences in terpenoid metabolic regulation between genotypes. Redundancy analysis demonstrated that <i>ACAT1</i> was negatively correlated with sesquiterpene and triterpene contents, while <i>FDPS2</i> showed a positive regulatory effect. qRT-PCR validation confirmed the reliability of transcriptomic findings. This study provides insights into the molecular regulatory network of terpenoid metabolism in stem lettuce and suggests a potential mechanistic basis for bitterness variation among genotypes. These findings offer theoretical foundations and identify key genetic targets for directional regulation of terpenoid biosynthesis, quality improvement, and enhanced utilization of stem lettuce.</p>

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Transcriptome and Metabolome Profiling of Different Genotypes and Growth Stages in Stem Lettuce Reveals Changes in Terpenoid Components

  • 期刊论文

  • 发表日期：

    2025年12月18日

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  • Haiwang Zhang,
  • Xueke Tian,
  • Yini Fu,
  • Xiaoqiang Wei,
  • Qiwen Zhong,
  • Shipeng Yang,
  • Xuemei Sun,
  • Lihui Wang

摘要

Sesquiterpenes and triterpenes are the primary contributors to the bitterness of stem lettuce (Lactuca sativa var. augustana), with significant bitterness variations observed among varieties with different leaf colors. To investigate the formation mechanisms of bitter compounds, two stem lettuce genotypes green-leaf (WS01) and purple-leaf (WS06) were used as experimental materials. By integrating metabolomic and transcriptomic analyses, we systematically compared the regulatory characteristics of terpenoid biosynthesis at the commercial harvest stage and the bolting stage. UPLC-MS/MS-based metabolomic profiling identified 33 terpenoid compounds, including 22 sesquiterpenes and 11 triterpenes. Among these, the sesquiterpene lactone lactucopicrin was the most abundant, accounting for approximately 60% of the total terpenoid content. Comparative analysis revealed higher total terpenoid content in the purple-leaf genotype. However, the green-leaf genotype accumulated more sesquiterpenes at the commercial harvest stage, while this trend reversed at the bolting stage. In contrast, triterpenes exhibited an opposite accumulation pattern, suggesting potential metabolic competition or antagonistic regulation between sesquiterpene and triterpene biosynthesis during development. Transcriptomic analysis identified 33,498 differentially expressed genes, including 2,387 novel genes. Enrichment analysis revealed that 18 terpenoid biosynthesis-related genes were significantly enriched in the "Sesquiterpenoid and triterpenoid biosynthesis" pathway (ko00909), displaying genotype- and stage-specific expression patterns. These genes were predominantly upregulated in the green-leaf genotype at the commercial harvest stage and in the purple-leaf genotype at the bolting stage, indicating spatiotemporal differences in terpenoid metabolic regulation between genotypes. Redundancy analysis demonstrated that ACAT1 was negatively correlated with sesquiterpene and triterpene contents, while FDPS2 showed a positive regulatory effect. qRT-PCR validation confirmed the reliability of transcriptomic findings. This study provides insights into the molecular regulatory network of terpenoid metabolism in stem lettuce and suggests a potential mechanistic basis for bitterness variation among genotypes. These findings offer theoretical foundations and identify key genetic targets for directional regulation of terpenoid biosynthesis, quality improvement, and enhanced utilization of stem lettuce.