MYB46 directly regulates the gene expression of secondary wall-associated cellulose synthases in Arabidopsis

Authors

  • Won-Chan Kim,

    1. Department of Horticulture and Department of Forestry, Michigan State University, East Lansing, MI, USA
    2. Department of Energy-Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI, 48824-1222, USA
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    • These authors contributed equally to this work.
  • Jae-Heung Ko,

    1. Department of Plant & Environmental New Resources, Kyung Hee University, Yongin-si, Gyeonggi-do, Korea
    2. Bioenergy Center, Kyung Hee University, Yongin, Korea
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    • These authors contributed equally to this work.
  • Joo-Yeol Kim,

    1. Department of Horticulture and Department of Forestry, Michigan State University, East Lansing, MI, USA
    2. Department of Energy-Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI, 48824-1222, USA
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  • Jungmook Kim,

    1. Department of Bioenergy Science and Technology, Chonnam National University, Buk-gu, Gwangju, Korea
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  • Hyeun-Jong Bae,

    1. Department of Bioenergy Science and Technology, Chonnam National University, Buk-gu, Gwangju, Korea
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  • Kyung-Hwan Han

    Corresponding author
    1. Department of Energy-Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI, 48824-1222, USA
    2. Department of Bioenergy Science and Technology, Chonnam National University, Buk-gu, Gwangju, Korea
    • Department of Horticulture and Department of Forestry, Michigan State University, East Lansing, MI, USA
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For correspondence (e-mail hanky@msu.edu).

Summary

Cellulose is the most abundant biopolymer on Earth. Three cellulose synthases (CESA4, CESA7 and CESA8) are necessary for cellulose production in the secondary cell walls of Arabidopsis. Little is known about how expression of these CESA genes is regulated. We recently identified a cis-regulatory element (M46RE) that is recognized by MYB46, which is a master switch for secondary wall formation in Arabidopsis. A genome-wide survey of promoter sequences for the presence of M46REs led to the hypothesis that MYB46 may function as a direct regulator of all three secondary wall-associated cellulose synthase genes: CESA4, CESA7 and CESA8. We tested this hypothesis using several lines of experimental evidence. All three CESA genes are highly up-regulated by both constitutive and inducible over-expression of MYB46 in planta. Using a steroid receptor-based inducible activation system, we show that MYB46 directly activates transcription of the three CESA genes. We then used an electrophoretic mobility shift assay and chromatin immunoprecipitation analysis to confirm that MYB46 protein directly binds to the promoters of the three CESA genes both in vitro and in vivo. Furthermore, ectopic up-regulation of MYB46 resulted in a significant increase of crystalline cellulose content in Arabidopsis. Taken together, we have identified MYB46 as a transcription factor that directly regulates all three secondary wall-associated CESA genes. Yeast one-hybrid screening identified additional transcription factors that regulate the CESA genes. However, none of the putative regulators appears to be regulated by MYB46, suggesting the multi-faceted nature of transcriptional regulation of secondary wall cellulose biosynthesis.

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