Brassinosteroid (BR) signaling has long been reported to have an effect on xylem development, but the detailed mechanism remains unclear, especially in tree species. In this study, we find PdC3H17, which was demonstrated to mediate xylem formation driven by auxin in our previous report, is also involved in BR-promoted xylem development. Y1H analysis, EMSA, and transcription activation assay confirmed that PdC3H17 was directly targeted by PdBES1, which is a key transcriptional regulator in BR signaling. Tissue specificity expression analysis and in situ assay revealed that PdC3H17 had an overlapping expression profile with PdBES1. Hormone treatment examinations verified that xylem phenotypes in PdC3H17 transgenic plants, which were readily apparent in normal condition, were attenuated by treatment with either brassinolide or the BR biosynthesis inhibitor propiconazole. The subsequent quantitative real-time polymerase chain reaction (qRT-PCR) analyses further revealed that BR converged with PdC3H17 to influence transcription of downstream xylem-related genes. Additionally, the enhancement of xylem differentiation by auxin in PdC3H17 overexpression plants was significantly attenuated compared with wild-type and dominant negative plants due to BR deficiency, which suggested that the BR- and auxin-responsive gene PdC3H17 acted as an mediation of these two hormones to facilitate xylem development. Taken together, our results demonstrate that BR signaling converges with auxin-mediated PdC3H17 to regulate xylem formation in Populus and thus provide insight into the regulation mechanism of BRs and the crosstalk with auxin signaling on xylem formation.

长期以来，已有报道称油菜素类固醇（BR）信号对木质部的发育有影响，但具体机制尚不清楚，尤其是在树种中。在这项研究中，我们发现PdC3H17在先前的研究中已证明可介导生长素驱动的木质部形成，并且也参与了BR促进木质部的发育。Y1H分析，EMSA和转录激活分析证实PdC3H17PdBES1是BR信号转导的关键转录调节因子，直接靶向。组织特异性表达分析和原位 分析表明 PdC3H17 的表达谱与 分贝1。激素治疗检查证实了木质部表型在PdC3H17通过用油菜素内酯或BR生物合成抑制剂丙环唑处理，可以减弱在正常情况下很容易出现的转基因植物。随后的定量实时聚合酶链反应（qRT-PCR）分析进一步揭示，BR与PdC3H17融合，影响下游木质部相关基因的转录。此外，生长素在体内促进木质部分化PdC3H17 由于BR缺乏，与野生型和显性负性植物相比，过表达植物显着减毒，这表明BR和生长素应答基因 PdC3H17充当这两种激素的中介以促进木质部的发育。两者合计，我们的结果表明BR信号与植物生长素介导的PdC3H17会合，以调节植物中木质部的形成。胡杨 从而深入了解BR的调控机制以及与生长素信号传导对木质部形成的串扰。