The FBA Motif-Containing Protein NpFBA1 Causes Leaf Curling and Reduces Resistance to Black Shank Disease in Tobacco

Plant leaf morphology has a great impact on plant drought resistance, ornamental research and leaf yield. In this study, we identified a new gene in Nicotiana plumbaginifolia, NpFBA1, that causes leaf curl. The results show that the NpFBA1 protein contains only one unique F-box associated (FBA) domain and does not have an F-box conserved domain. Phylogenetic analysis placed this gene and other Nicotiana FBA genes on a separate branch, and the NpFBA1 protein localized to the nucleus and cytoplasm. The expression of NpFBA1 was induced by black shank pathogen (Phytophthora parasitica var. nicotianae) infection and treatment with salicylic acid (SA) and methyl jasmonate (MeJA). NpFBA1-overexpressing transgenic lines showed leaf curling and aging during the rosette phase. During the bolting period, the leaves were curly and rounded, and the plants were dwarfed. In addition, NpFBA1-overexpressing lines were more susceptible to disease than wild-type (WT) plants. Further studies revealed that overexpression of NpFBA1 significantly downregulated the expression of auxin response factors such as NtARF3 and the lignin synthesis genes NtPAL, NtC4H, NtCAD2, and NtCCR1 in the leaves. In conclusion, NpFBA1 may play a key role in regulating leaf development and the response to pathogen infection.