CCR4-associated factor CAF1I promotes plant growth and ectomycorrhizal formation in Populus tomentosa

Ectomycorrhizal (ECM) fungi preferentially form symbiotic associations with many woody plants. However, the genes regulating ECM formation and their functions in host plants remain poorly understood. In this study, PtoCAF1I gene from Populus tomentosa was isolated and functionally characterized. Bioinformatics analysis revealed that PtoCAF1I contains a conserved RNase D structural domain. Tissue expression analysis showed that PtoCAF1I was more highly expressed in roots than other tissues (leaves and stems). Overexpression of PtoCAF1I in P. tomentosa resulted in significantly greater shoot height, number of branches, and biomass in potted seedlings compared with wild-type (WT) plants. Inoculation experiments revealed that overexpression of PtoCAF1I significantly increased the total ECM rate compared with WT poplar inoculated with Cenococcum geophilum, whereas PtoCAF1I RNA interference (RNAi) lines presented an opposite trend. These results suggest that PtoCAF1I not only promotes poplar growth and branch development but also enhances the formation of ECM roots upon inoculation with C. geophilum.