The termination of floral meristem (FM) activity is essential for the normal development of reproductive floral organs. During this process, KNUCKLES (KNU), a C2H2-type zinc finger protein, crucially regulates FM termination by directly repressing the expression of both the stem cell identity gene WUSCHEL (WUS) and the stem cell marker gene CLAVATA3 (CLV3) to abolish the WUS-CLV3 feedback loop required for FM maintenance. In addition, phytohormones auxin and cytokinin are involved in FM regulation. However, whether KNU modulates auxin and cytokinin activities for FM determinacy control remains unclear. Here, we show that the auxin distribution and the cytokinin activity mediated by KNU in Arabidopsis (Arabidopsis thaliana) promote the termination of FM during stage 6 of flower development. Mutation of KNU leads to altered distribution of auxin and cytokinin in the FM of a stage 6 floral bud. Moreover, KNU directly represses the auxin transporter gene PIN-FORMED1 (PIN1) and the cytokinin biosynthesis gene ISOPENTENYLTRANSFERASE7 (IPT7) via mediating H3K27me3 deposition on these two loci to regulate auxin and cytokinin activities. Our study presents a molecular regulatory network that elucidates how the transcriptional repressor KNU integrates and modulates the activities of auxin and cytokinin, thus securing the timed FM termination.

中文翻译：

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KNUCKLES 通过控制生长素分布和细胞分裂素活性来调节花分生组织终止


花分生组织 （FM） 活性的终止对于生殖花器官的正常发育至关重要。在此过程中，C2H2 型锌指蛋白 KNUCKLES （KNU） 通过直接抑制干细胞身份基因 WUSCHEL （WUS） 和干细胞标志基因 CLAVATA3 （CLV3） 的表达来消除 FM 维持所需的 WUS-CLV3 反馈回路，从而关键地调节 FM 终止。此外，植物激素生长素和细胞分裂素参与 FM 调节。然而，KNU 是否调节生长素和细胞分裂素活性以控制 FM 决定性仍不清楚。在这里，我们表明拟南芥 （Arabidopsis thaliana） 中 KNU 介导的生长素分布和细胞分裂素活性促进了花发育第 6 阶段 FM 的终止。KNU 突变导致生长素和细胞分裂素在 6 期花芽 FM 中的分布发生变化。此外，KNU 通过介导 H3K27me3 沉积在这两个基因座上，直接抑制生长素转运蛋白基因 PIN-FORMED1 （PIN1） 和细胞分裂素生物合成基因 ISOPENTENYLTRANSFERASE7 （IPT7），以调节生长素和细胞分裂素活性。我们的研究提出了一个分子调控网络，阐明了转录抑制因子 KNU 如何整合和调节生长素和细胞分裂素的活性，从而确保定时 FM 终止。