Jin Yanli, Yu Chunyan, Jiang Chunmei, Guo Xiaotong, Li Bei, Wang Cuiting, Kong Fanjing, Zhang Hongxia, Wang Haihai
College of Agriculture, Ludong University, Yantai, China.
National Key Laboratory of Plant Molecular Genetics, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China.
Front Plant Sci. 2020 Apr 24;11:468. doi: 10.3389/fpls.2020.00468. eCollection 2020.
In angiosperm trees, the gelatinous layer (G-layer) takes a great part of the fiber cell wall in the tension wood (TW). However, the mechanism underlying G-layer formation in poplar is largely unknown. In this work, we demonstrate that G-layer formation in poplar TW cells is regulated by brassinosteroid (BR) and its signaling. , a key BR biosynthesis gene, was predominantly expressed in the xylem of TW, accompanied with a relatively higher castasterone (CS) accumulation, than in the xylem of opposite wood (OW). A wider expression zone of BZR1, a key transcriptional factor in BR singling pathway, was also observed in G-fiber cells on TW side than in wood fiber cells on the OW side, as indicated by immunohistochemistry assays. Transgenic poplar plants overexpressing produced thicker G-layer with higher cellulose proportion, and accumulated more BZR1 protein in the xylem of TW than did the wild type (WT) plants. Expression of most TW-associated , which were induced by 2, 4-epibrassinolide, an active BR, and inhibited by brassinazole, a BR biosynthesis inhibitor, were also up-regulated in the xylem of TW in transgenic plants compared to that in WT plants. Further studies with dual-luciferase assays demonstrated that the promoters of were activated by PtiMYB128, a TW specific transcription factor, which was then regulated by BZR1. All these results indicate that BR plays a crucial role in the G-layer formation of TW fiber cells by regulating the expression of , , and in poplar.
在被子植物树木中，凝胶层（G层）在张力木（TW）的纤维细胞壁中占很大一部分。然而，杨树中G层形成的机制在很大程度上尚不清楚。在这项研究中，我们证明杨树TW细胞中G层的形成受油菜素内酯（BR）及其信号传导的调控。一个关键的BR生物合成基因在TW的木质部中大量表达，与相对的木材（OW）的木质部相比，伴随着较高的菜甾酮（CS）积累。免疫组织化学分析表明，BR信号通路中的关键转录因子BZR1在TW侧的G纤维细胞中的表达区域比OW侧的木纤维细胞中的更宽。过表达的转基因杨树植株产生了更厚的G层，纤维素比例更高，并且在TW的木质部中比野生型（WT）植株积累了更多的BZR1蛋白。与WT植株相比，大多数与TW相关的基因的表达在转基因植株TW的木质部中也上调，这些基因被活性BR 2,4-表油菜素内酯诱导，并被BR生物合成抑制剂油菜唑抑制。双荧光素酶分析的进一步研究表明，这些基因的启动子被TW特异性转录因子PtiMYB128激活，而PtiMYB128又受BZR1调控。所有这些结果表明，BR通过调节杨树中、和的表达，在TW纤维细胞的G层形成中起关键作用。
