Poplar co-chaperone PdBAG12 negatively regulates wood formation by decreasing nuclear localization of PdC3H17

Abstract

B-cell lymphoma 2 (Bcl−2)-associated athanogene (BAG) proteins, as the molecular chaperones, play prominent roles in regulating plant growth, development, and stress responses. Currently, it remains unclear the biological roles of BAG proteins in tree species. This study provided evidence showing that poplar BAG family member PdBAG12 participates in the regulation of wood structure and property. PdBAG12 was preferentially expressed in wood-forming cells in stems. Genome editing PdBAG12 gene in poplar resulted in increases of cambial cell layer number, fiber cell length, the ratio of xylem to phloem width, and the ratio of cellulose to lignin content. However, transgenic poplar lines overexpressing PdBAG12 showed opposite phenotypes. Importantly, knockout or overexpression of PdBAG12 did not affect plant height or stem diameter. Biochemical assays revealed that PdBAG12 interacted with PdC3H17, a positive regulator of wood formation in poplar. The interaction between each other led to reduced nuclear localization of PdC3H17, and inhibited its direct activation of xylem differentiation-associated PdSAG101a expression, thereby suppressing xylem differentiation. Our results indicated that PdBAG12 facilitate‌s fine regulation of xylem differentiation by PdC3H17 during wood formation. Further, PdBAG12-edited poplar lines possess improved wood properties and have the potential in the pulping, papermaking, and bioenergy applications.