J Integr Plant Biol. ›› 2018, Vol. 60 ›› Issue (6): 514-528.DOI: 10.1111/jipb.12638

• Plant-abiotic Interactions • Previous Articles    

KNAT7 positively regulates xylan biosynthesis by directly activating IRX9 expression in Arabidopsis

Jun-Bo He1,2, Xian-Hai Zhao1,2, Ping-Zhou Du3†, Wei Zeng4, Cherie T Beahan4, Yu-Qi Wang3,5, Hui-Ling Li1,2,6, Antony Bacic4 and Ai-Min Wu1,2*   

  1. 1State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, South China Agricultural University, Guangzhou 510642, China
    2Guangdong Key Laboratory for Innovative Development and Utilization of Forest Plant Germplasm, College of Forestry and Landscape Architecture, South China Agricultural University, Guangzhou 510642, China
    3College of Life Sciences, South China Agricultural University, Guangzhou 510642, China
    4ARC Centre of Excellence in Plant Cell Walls, School of BioSciences, The University of Melbourne, Parkville VIC 3010, Australia
    5Boyce Thompson Institute for Plant Research, Ithaca, NY 14853, USA
    6Provincial Key Laboratory of Agrobiology, Jiangsu Academy of Agricultural Sciences, Nanjing 210014, China
  • Received:2017-10-29 Accepted:2018-01-28 Published:2018-06-01
  • About author:Current address: Key Laboratory of Cell Proliferation and Regulation Biology of Ministry of Education, College of Life Science, Beijing Normal University, Beijing 100875, China
    *Correspondence: Email: Ai-Min Wu (wuaimin@scau.edu.cn)


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.

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