Numerous proteins involved in cellulose biosynthesis and assembly have been functionally characterized. Nevertheless, we have a limited understanding of the mechanisms underlying the transcriptional regulation of the genes that encode… Click to show full abstract
Numerous proteins involved in cellulose biosynthesis and assembly have been functionally characterized. Nevertheless, we have a limited understanding of the mechanisms underlying the transcriptional regulation of the genes that encode these proteins. Here, we report that HOMEODOMAIN GLABROUS2 (HDG2), a Homeobox-Leucine Zipper IV transcription factor, regulates cellulose biosynthesis in Arabidopsis (Arabidopsis thaliana) seed coat mucilage. HDG2 is a transcriptional activator with the transactivation domain located within its Leucine-Zipper domain. Transcripts of HDG2 were detected specifically in seed coat epidermal cells with peak expression at 10 d postanthesis. Disruptions of HDG2 led to seed coat mucilage with aberrant morphology due to a reduction in its crystalline cellulose content. Electrophoretic mobility shift and yeast one-hybrid assays, together with chromatin immunoprecipitation and quantitative PCR, provided evidence that HDG2 directly activates CELLULOSE SYNTHASE5 (CESA5) expression by binding to the L1-box cis-acting element in its promoter. Overexpression of CESA5 partially rescued the mucilage defects of hdg2-3. Together, our data suggest that HDG2 directly activates CESA5 expression and thus is a positive regulator of cellulose biosynthesis in seed coat mucilage.
               
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