PtiCYP85A3, a BR C-6 Oxidase Gene, Plays a Critical Role in Brassinosteroid-Mediated Tension Wood Formation in Poplar
PtiCYP85A3, a BR C-6 Oxidase Gene, Plays a Critical Role in Brassinosteroid-Mediated Tension Wood Formation in Poplar
复制标题
BR C-6 氧化酶基因 PtiCYP85A3 在油菜素类固醇介导的杨树张力木材形成中发挥关键作用
DOI：
10.3389/fpls.2020.00468
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发表时间：
2020-04-24
影响因子：
5.6
通讯作者：
Wang, Haihai
中科院分区：
文献类型：
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作者：
Jin, Yanli;Yu, Chunyan;Wang, Haihai
在被子植物中，胶状层（G 层）占据了张力木（TW）中纤维细胞壁的很大一部分。然而，杨树 G 层形成的机制在很大程度上尚不清楚。在这项工作中，我们证明杨树 TW 细胞中 G 层的形成受到油菜素类固醇 (BR) 及其信号传导的调节。 PtiCYP85A3是BR生物合成的关键基因，主要在TW的木质部中表达，与相反木材（OW）的木质部相比，伴随着相对较高的卡斯特酮（CS）积累。免疫组织化学检测表明，TW 侧的 G 纤维细胞中 BZR1（BR 单信号通路中的关键转录因子）的表达区域比 OW 侧的木纤维细胞更宽。过表达PtiCYP85A3的转基因杨植物比野生型(WT)植物产生更厚的G层和更高的纤维素比例，并在TW的木质部中积累更多的BZR1蛋白。大多数与 TW 相关的 CesAs 的表达，由 2, 4-表油菜素内酯（一种活性 BR）诱导，并由 BR 生物合成抑制剂芸苔素唑（BR 生物合成抑制剂）抑制，与 WT 植物相比，在转基因植物的 TW 木质部中表达也上调。双荧光素酶测定的进一步研究表明，PtiCesAs 的启动子被 TW 特异性转录因子 PtiMYB128 激活，然后受 BZR1 调节。所有这些结果表明，BR通过调节杨树中BZR1、PtiMYB128和PtiCesAs的表达，在TW纤维细胞G层形成中发挥着至关重要的作用。
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. PtiCYP85A3, 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 PtiCYP85A3 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 CesAs, 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 PtiCesAs 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 BZR1, PtiMYB128, and PtiCesAs in poplar.