PtiCYP85A3 , a BR C-6 Oxidase Gene, Plays a Critical Role in Brassinosteroid-Mediated Tension Wood Formation in Poplar

• Published in: Frontiers in plant science 2020-04, Vol.11, p.468-468
• Main Authors: Jin, Yanli, Yu, Chunyan, Jiang, Chunmei, Guo, Xiaotong, Li, Bei, Wang, Cuiting, Kong, Fanjing, Zhang, Hongxia, Wang, Haihai
• Format: Article
• Language: English
• Subjects: brassinosteroids; G-layer; Plant Science; poplar; PtiCYP85A3; tension wood; xylem
• ISSN: 1664-462X; 1664-462X
• DOI: 10.3389/fpls.2020.00468

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.