Wang Yiping, Xu Yan, Pei Shengqiang, Lu Mingmin, Kong Yingzhen, Zhou Gongke, Hu Ruibo
Key Laboratory of Biofuels, Shandong Provincial Key Laboratory of Energy Genetics, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, PR China.
University of Chinese Academy of Sciences, Beijing, PR China.
J Exp Bot. 2020 Jul 6;71(14):4125-4139. doi: 10.1093/jxb/eraa189.
As a major hemicellulose component of plant cell walls, xylans play a determining role in maintaining the wall structure. However, the mechanisms of transcriptional regulation of xylan biosynthesis remain largely unknown. Arabidopsis seed mucilage represents an ideal system for studying polysaccharide biosynthesis and modifications of plant cell walls. Here, we identify KNOTTED ARABIDOPSIS THALIANA 7 (KNAT7) as a positive transcriptional regulator of xylan biosynthesis in seed mucilage. The xylan content was significantly reduced in the mucilage of the knat7-3 mutant and this was accompanied by significantly reduced expression of the xylan biosynthesis-related genes IRREGULAR XYLEM 14 (IRX14) and MUCILAGE MODIFIED 5/MUCILAGE-RELATED 21 (MUM5/MUCI21). Electrophoretic mobility shift assays, yeast one-hybrid assays, and chromatin immunoprecipitation with quantitative PCR verified the direct binding of KNAT7 to the KNOTTED1 (KN1) binding site [KBS,TGACAG(G/C)T] in the promoters of IRX7, IRX14, and MUM5/MUCI21 in vitro, in vivo, and in planta. Furthermore, KNAT7 directly activated the expression of IRX14 and MUM5/MUCI21 in transactivation assays in mesophyll protoplasts, and overexpression of IRX14 or MUM5/MUCI21 in knat7-3 partially rescued the defects in mucilage adherence. Taken together, our results indicate that KNAT7 positively regulates xylan biosynthesis in seed-coat mucilage via direct activation of the expression of IRX14 and MUM5/MUCI21.
作为植物细胞壁的主要半纤维素成分，木聚糖在维持细胞壁结构中起决定性作用。然而，木聚糖生物合成的转录调控机制仍 largely 未知。拟南芥种子黏液是研究植物细胞壁多糖生物合成和修饰的理想系统。在此，我们鉴定出拟南芥结瘤蛋白 7（KNAT7）是种子黏液中木聚糖生物合成的正转录调节因子。在 knat7 - 3 突变体的黏液中，木聚糖含量显著降低，同时木聚糖生物合成相关基因不规则木质部 14（IRX14）和黏液修饰 5/黏液相关 21（MUM5/MUCI21）的表达也显著降低。电泳迁移率变动分析、酵母单杂交分析以及染色质免疫沉淀定量 PCR 在体外、体内和植物体内验证了 KNAT7 直接与 IRX7、IRX14 和 MUM5/MUCI21 启动子中的结瘤蛋白 1（KN1）结合位点 [KBS，TGACAG(G/C)T] 结合。此外，在叶肉原生质体的反式激活分析中，KNAT7 直接激活了 IRX14 和 MUM5/MUCI21 的表达，并且在 knat7 - 3 中过表达 IRX14 或 MUM5/MUCI21 部分挽救了黏液黏附缺陷。综上所述，我们的结果表明 KNAT7 通过直接激活 IRX14 和 MUM5/MUCI21 的表达正向调节种皮黏液中的木聚糖生物合成。
