Chemical defense systems involving tryptophan-derived secondary metabolites (TDSMs) and salicylic acid (SA) are induced by general nonself signals and pathogen signals, respectively, in Arabidopsis thaliana. Whether and how these chemical defense systems are connected and balanced is largely unknown. In this study, we identified the AVRRPT2-INDUCED GENE2A (AIG2A) and AIG2B genes as gatekeepers that prevent activation of SA defense systems by TDSMs. These genes also were identified as important contributors to natural variation in disease resistance among A. thaliana natural accessions. The loss of AIG2A and AIG2B function leads to upregulation of both SA and TDSM defense systems. Suppressor screens and genetic analysis revealed that a functional TDSM system is required for the upregulation of the SA pathway in the absence of AIG2A and AIG2B, but not vice versa. Furthermore, the AIG2A and AIG2B genes are co-induced with TDSM biosynthesis genes by general pathogen elicitors and nonself signals, thereby functioning as a feedback control of the TDSM defense system, as well as limiting activation of the SA defense system by TDSMs. Thus, this study uncovers an AIG2A- and AIG2B-mediated mechanism that fine-tunes and balances SA and TDSM chemical defense systems in response to nonpathogenic and pathogenic microbes.

中文翻译：

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AIG2A 和 AIG2B 通过拟南芥中色氨酸衍生的次级代谢来限制水杨酸调节的防御的激活。

在拟南芥中，涉及色氨酸衍生的次级代谢产物（TDSM）和水杨酸（SA）的化学防御系统分别由一般非自身信号和病原体信号诱导。这些化学防御系统是否以及如何相互连接和平衡在很大程度上尚不清楚。在这项研究中，我们确定了 AVRRPT2 诱导的 GENE2A (AIG2A) 和 AIG2B 基因作为守门人，阻止 TDSM 激活 SA 防御系统。这些基因也被确定为拟南芥天然种质抗病性自然变异的重要贡献者。AIG2A 和 AIG2B 功能的丧失导致 SA 和 TDSM 防御系统的上调。抑制子筛选和遗传分析表明，在 AIG2A 和 AIG2B 缺失的情况下，功能性 TDSM 系统是 SA 途径上调所必需的，但反之则不然。此外，AIG2A和AIG2B基因与TDSM生物合成基因由一般病原体诱导子和非自身信号共同诱导，从而起到TDSM防御系统的反馈控制的作用，并限制TDSM对SA防御系统的激活。因此，这项研究揭示了 AIG2A 和 AIG2B 介导的机制，可微调和平衡 SA 和 TDSM 化学防御系统，以响应非病原性和病原性微生物。