PMID:22889423

Citation	'Kim, WC, Ko, JH, Kim, JY, Kim, JM, Bae, HJ and Han, KH (2012) MYB46 directly regulates the gene expression of secondary wall-associated cellulose synthases in Arabidopsis. Plant J. '
Abstract	Cellulose is the most abundant biopolymer on Earth. In the secondary cell walls of Arabidopsis, three cellulose synthases (CESA4, CESA7, and CESA8) are necessary for cellulose production. Little is known about how the expression of these CESA genes is regulated. We recently identified a cis-regulatory element ('M46RE') recognized by MYB46, which is a master switch for secondary wall formation in Arabidopsis. A genome-wide survey of promoter sequences for the M46RE led to a hypothesis that MYB46 may function as a direct regulator of all three secondary wall-associated cellulose synthases, CESA4, CESA7 and CESA8. We tested this hypothesis using several lines of experimental evidence. All of the three CESA genes are highly upregulated in both constitutive and inducible over-expression of MYB46 in planta. Using a steroid receptor-based inducible activation system, we show that MYB46 directly activates the transcription of the three CESA genes. We then used electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP) analysis to confirm that MYB46 protein directly binds the promoters of the three CESA genes both in vitro and in vivo. Furthermore, ectopic upregulation of MYB46 resulted in a significant increase of crystalline cellulose content in Arabidopsis. Taken together, we identify 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 CESAs. However, none of the putative regulators appears to be regulated by MYB46 (Ko et al., 2009; Kim et al., 2012), suggesting multifaceted nature of the transcriptional regulation of secondary wall cellulose biosynthesis. © 2012 The Authors. The Plant Journal © 2012 Blackwell Publishing Ltd.
Links	PubMed Online version:10.1111/j.1365-313X.2012.05124.x
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