State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, South China Agricultural University, Guangzhou 510642, China.
Guangdong Key Laboratory for Innovative Development and Utilization of Forest Plant Germplasm, College of Forestry and Landscape Architecture, South China Agricultural University, Guangzhou 510642, China.
J Integr Plant Biol. 2018 Jun;60(6):514-528. doi: 10.1111/jipb.12638. Epub 2018 Apr 30.
Xylan is the major plant hemicellulosic polysaccharide in the secondary cell wall. The transcription factor KNOTTED-LIKE HOMEOBOX OF ARABIDOPSIS THALIANA 7 (KNAT7) regulates secondary cell wall biosynthesis, but its exact role in regulating xylan biosynthesis remains unclear. Using transactivation analyses, we demonstrate that KNAT7 activates the promoters of the xylan biosynthetic genes, IRREGULAR XYLEM 9 (IRX9), IRX10, IRREGULAR XYLEM 14-LIKE (IRX14L), and FRAGILE FIBER 8 (FRA8). The knat7 T-DNA insertion mutants have thinner vessel element walls and xylary fibers, and thicker interfascicular fiber walls in inflorescence stems, relative to wild-type (WT). KNAT7 overexpression plants exhibited opposite effects. Glycosyl linkage and sugar composition analyses revealed lower xylan levels in knat7 inflorescence stems, relative to WT; a finding supported by labeling of inflorescence walls with xylan-specific antibodies. The knat7 loss-of-function mutants had lower transcript levels of the xylan biosynthetic genes IRX9, IRX10, and FRA8, whereas KNAT7 overexpression plants had higher mRNA levels for IRX9, IRX10, IRX14L, and FRA8. Electrophoretic mobility shift assays indicated that KNAT7 binds to the IRX9 promoter. These results support the hypothesis that KNAT7 positively regulates xylan biosynthesis.
木聚糖是次生细胞壁中主要的植物半纤维素多糖。拟南芥 KNOTTED-LIKE HOMEOBOX OF ARABIDOPSIS THALIANA 7（KNAT7）转录因子调节次生细胞壁生物合成，但它在调节木聚糖生物合成中的确切作用尚不清楚。通过转录激活分析，我们证明 KNAT7 激活木聚糖生物合成基因 IRREGULAR XYLEM 9（IRX9）、IRX10、IRREGULAR XYLEM 14-LIKE（IRX14L）和 FRAGILE FIBER 8（FRA8）的启动子。knat7 T-DNA 插入突变体在花序茎中具有更薄的导管壁和木质纤维，以及更厚的束间纤维壁，与野生型（WT）相比。KNAT7 过表达植物表现出相反的效果。糖基连接和糖组成分析显示，knat7 花序茎中的木聚糖水平较低，相对于 WT；这一发现得到了花序壁用木聚糖特异性抗体标记的支持。knat7 功能丧失突变体的木聚糖生物合成基因 IRX9、IRX10 和 FRA8 的转录水平较低，而 KNAT7 过表达植物的 IRX9、IRX10、IRX14L 和 FRA8 的 mRNA 水平较高。电泳迁移率变动分析表明，KNAT7 结合到 IRX9 启动子上。这些结果支持了 KNAT7 正向调节木聚糖生物合成的假说。
