Cas9/gRNA-Mediated Mutations in and Reveal Redundant Roles in Modulating Wood Cell Size and SCW Synthesis in Poplar.

Fasciclin-like arabinogalactan proteins (FLAs) play an important role in plant development and adaptation to the environment. However, the roles of FLAs in wood formation remain poorly understood. Here, we identified a total of 50 genes in poplar. They were classified into four groups: A to D, among which group A was the largest group with 28 members clustered into four branches. Most of group A were dominantly expressed in developing xylem based on microarray and RT-qPCR data. The roles of and in group A were investigated via the Cas9/gRNA-induced mutation lines. Loss of and increased stem length and diameter in double mutants, but not in or single mutants. Further, our findings indicated that the mutants enlarged the cell size of xylem fibers and vessels, suggesting a negative modulation in stem xylem cell size. In addition, wood lignin content in the mutants was increased by nearly 9%, and the lignin biosynthesis-related genes were significantly up-regulated in the mutants, in agreement with the increase in wood lignin content. Overall, Cas9/gRNA-mediated mutations in and reveal redundant roles in modulating wood cell size and secondary cell wall (SCW) synthesis in poplar.