PagHCF106 negatively regulates drought stress tolerance in poplar (<i>Populus alba × Populus glandulosa</i>) by modulating stomatal aperture

Modulation of stomatal development and movement is a promising approach for creating water-conserving plants. Here, we identified and characterized the PagHCF106 gene of poplar (Populus alba × Populus glandulosa). The PagHCF106 protein localized predominantly to the chloroplast and the PagHCF106 gene exhibited a tissue-specific expression pattern. Overexpression of PagHCF106 rescued the reduced stomatal aperture and increased drought resistance of the hcf106 Arabidopsis mutant. Clustered regularly interspaced palindromic repeats (CRISPR)/Cas9-mediated genome editing introduced mutations in the core region of the PagHCF106 promoter, which was required for its activity, as confirmed by the GUS staining assay. Mutation of the PagHCF106 promoter reduced stomatal opening and water loss in poplar. In addition, the genome-edited poplar lines accumulated high levels of hydrogen peroxide in guard cells. Taken together, these results suggest that PagHCF106 negatively regulates drought stress tolerance by modulating stomatal aperture, which might be associated with reactive oxygen species production. We propose that modification of the PagHCF106 promoter might be an efficient strategy for enhancing drought stress tolerance in poplar.