Rehmannia glutinosa production is affected by the replanting disease, which involves autotoxic harm mediated by specific endogenous allelochemicals in root exudates. Many phenolics that act as allelochemical agents are mostly phenylpropanoid products of secondary metabolism in plants. Phenylalanine ammonia-lyase (PAL) is the first enzyme that catalyses the deamination of l-phenylalanine for entrance into the phenylpropanoid pathway. PAL family genes have been isolated and functionally characterized in many plant species. However, PAL family genes involved in phenolic biosynthesis remain largely uncharacterized in R. glutinosa. Here, we identified and characterized four PAL family genes (RgPAL2 to RgPAL5) in the species whose sequences exhibited highly conserved domains of PALs according to in silico analysis, implying their potential function in phenolic biosynthesis. Overexpression of RgPALs in R. glutinosa enhanced phenolic production, verifying that RgPAL family genes participate in phenolic biosynthesis pathways. Moreover, we found that the release of several allelopathic phenolics from the roots of RgPAL-overexpressing transgenic R. glutinosa increased, implying that the RgPALs positively promote their release. Importantly, under continuous monoculture stress, we found that the RgPAL transgenic plants exhibited more significant autotoxic harm than did non-transgenic (WT) plants by activating the phenolics/phenylpropanoid pathway, indicating that RgPAL family genes function as positive regulators of the replanting disease development in R. glutinosa. This study revealed that RgPAL family genes are involved in the biosynthesis and release of several phenolics and positively control the replanting disease development in R. glutinosa, laying a foundation for further clarification of the molecular mechanisms underlying the disease formation.

中文翻译：

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参与酚类生物合成的RgPAL家族基因的过表达促进地黄再植病害的发展

地黄生产受再植病害的影响，其涉及由根系分泌物中特定的内源性化感物质介导的自毒伤害。许多作为化感剂的酚类物质大多是植物次生代谢的苯丙烷类产物。苯丙氨酸解氨酶 (PAL) 是第一种催化 l-苯丙氨酸脱氨以进入苯丙烷途径的酶。PAL 家族基因已在许多植物物种中被分离和功能表征。然而，参与酚类生物合成的 PAL 家族基因在 R. glutinosa 中基本上没有特征。在这里，我们鉴定并表征了物种中的四个 PAL 家族基因（RgPAL2 到 RgPAL5），根据计算机分析，这些基因的序列表现出高度保守的 PAL 结构域，暗示它们在酚类生物合成中的潜在功能。RgPALs 在 R. glutinosa 中的过度表达增强了酚类物质的产生，证实了 RgPAL 家族基因参与了酚类生物合成途径。此外，我们发现从过表达 RgPAL 的转基因 R. glutinosa 根部释放的几种化感酚类物质增加，这意味着 RgPAL 积极促进它们的释放。重要的是，在持续的单一栽培胁迫下，我们发现 RgPAL 转基因植物通过激活酚类/苯丙烷途径表现出比非转基因 (WT) 植物更显着的自毒危害，表明 RgPAL 家族基因作为重植病害发展的正调节因子在 R. glutinosa 中。