BlOFP1 is associated with reduced secondary cell wall formation and interacts with BlKNOX9 and BlBLH9 in Betula...

Timber quality is strongly influenced by the structure of the secondary cell wall (SCW). Ovate family proteins (OFPs) have been reported to regulate SCW formation in Arabidopsis. However, the functions of OFP proteins in woody plants remain unclear. In this study, an OFP gene, BlOFP1, was identified by co-expression analysis in Betula luminifera. BlOFP1 was co-expressed with multiple genes associated with lignin and cellulose biosynthesis. The subcellular localization showed that BlOFP1 was localized in the nucleus of tobacco leaf epidermal cells. Overexpression of BlOFP1 in Arabidopsis reduced cellulose, hemicellulose, and lignin contents and resulted in thinner SCW. In B. luminifera hairy roots, overexpression of BlOFP1 also led to thinner SCW, suggesting that elevated BlOFP1 expression is associated with reduced SCW formation in these experimental systems. Yeast two-hybrid, bimolecular fluorescence complementation and co-immunoprecipitation assays further showed that BlOFP1 physically interacted with BlKNOX9 and BlBLH9. Overall, our results suggest that BlOFP1 is associated with reduced SCW formation in these experimental systems, whereas the endogenous function of BlOFP1 in B. luminifera remains to be established. BlOFP1 may act together with BlKNOX9 and BlBLH9 in a proposed regulatory module.