The plant-specific TEOSINTE BRANCHED1/CYCLOIDEA/PROLIFERATING CELL FACTOR (TCP) transcription factor family is most closely associated with regulating plant developmental programs. Recently, TCPs were also shown to mediate host immune signaling, both as targets of pathogen virulence factors and as regulators of plant defense genes. However, comprehensive characterization of TCP gene targets is still lacking. Loss of function of the class I TCP gene AtTCP8 attenuates early immune signaling and, when combined with mutations in AtTCP14 and AtTCP15, additional layers of defense signaling in Arabidopsis (Arabidopsis thaliana). Here, we focus on TCP8, the most poorly characterized of the three to date. We used chromatin immunoprecipitation and RNA sequencing to identify TCP8-bound gene promoters and differentially regulated genes in the tcp8 mutant; these datasets were heavily enriched in signaling components for multiple phytohormone pathways, including brassinosteroids (BRs), auxin, and jasmonic acid. Using BR signaling as a representative example, we showed that TCP8 directly binds and activates the promoters of the key BR transcriptional regulatory genes BRASSINAZOLE-RESISTANT1 (BZR1) and BRASSINAZOLE-RESISTANT2 (BZR2/BES1). Furthermore, tcp8 mutant seedlings exhibited altered BR-responsive growth patterns and complementary reductions in BZR2 transcript levels, while TCP8 protein demonstrated BR-responsive changes in subnuclear localization and transcriptional activity. We conclude that one explanation for the substantial targeting of TCP8 alongside other TCP family members by pathogen effectors may lie in its role as a modulator of BR and other plant hormone signaling pathways.

中文翻译：

---

I 类 TCP 转录因子 AtTCP8 调节关键的油菜素类固醇反应基因。

植物特有的 TEOSINTE BRANCHED1/CYCLOIDEA/PROLIFERATING CELL FACTOR (TCP) 转录因子家族与调节植物发育程序密切相关。最近，TCP 还被证明可以介导宿主免疫信号传导，既可以作为病原体毒力因子的靶标，也可以作为植物防御基因的调节剂。然而，TCP 基因靶点的全面表征仍然缺乏。I 类 TCP 基因 AtTCP8 功能丧失会减弱早期免疫信号传导，并且当与 AtTCP14 和 AtTCP15 突变结合时，拟南芥中会产生额外的防御信号传导层。在这里，我们重点关注 TCP8，它是迄今为止这三个协议中特征最差的一个。我们使用染色质免疫沉淀和RNA测序来鉴定tcp8突变体中TCP8结合基因启动子和差异调节基因；这些数据集富含多种植物激素途径的信号成分，包括油菜素类固醇 (BR)、生长素和茉莉酸。以BR信号传导作为代表性例子，我们发现TCP8直接结合并激活关键BR转录调控基因BRASSINAZOLE-RESISTANT1 (BZR1)和BRASSINAZOLE-RESISTANT2 (BZR2/BES1)的启动子。此外，tcp8突变体幼苗表现出改变的BR响应性生长模式和BZR2转录水平的互补降低，而TCP8蛋白在亚核定位和转录活性方面表现出BR响应性变化。我们得出的结论是，TCP8 与其他 TCP 家族成员一起被病原体效应子实质性靶向的一种解释可能在于它作为 BR 和其他植物激素信号通路调节剂的作用。