An AC-type element mediates transactivation of secondary cell wall carbohydrate-active enzymes by PttMYB021, the PopulusMYB46 orthologue
© Ezcurra et al; licensee BioMed Central Ltd. 2011
Published: 13 September 2011
The transcription factor MYB46, together with its redundant paralog MYB83, regulates expression of secondary cell wall biosynthesis genes in Arabidopsis [reviewed in 1].
We isolated the Populus MYB46 ortholog, PtxtMYB021 from hybrid aspen (Populus tremula x tremuloides) . Transiently expressed MYB021 transactivated gene promoters of Populus xylan-active enzymes GT43A, GT43B and Xyn10A. Analysis of conserved motifs within these promoters identified the sequence CCACCAAC, which is similar to the AC elements mediating transactivation by MYB transcription factors during lignin biosynthesis, and we showed that this motif is enriched in xylem-specific carbohydrate active enzyme (CAZyme) promoters.
To establish whether the AC-type motif in CAZyme promoters is important for their function, we analyzed loss-of-function and gain-of-function GUS reporter constructs of the GT43A promoter in a transient transcription assay, by co-infiltration with a 35S:MYB021 effector in Nicotiana benthamiana leaves.
Results and discussion
Sequence overlap in AC motifs.
CCCACC T ACC
c CACC T ACC
c CACC T ACC
t c ACCAAC
The AC regulatory element, here preliminarily redefined as the sequence CCACCAAC, is a true “lignocellulose synthesis response element”, mediating MYB46-dependent transactivation of the whole secondary cell wall gene program. This knowledge will enable inference of MYB46-centered regulatory networks in different species, through bioinformatic analysis.
We thank David Caparrós-Ruiz for helpful comments and discussions.
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