| Summary: | 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 <i>Nicotiana plumbaginifolia</i>, <i>NpFBA1</i>, that causes leaf curl. The results show that the <i>NpFBA1</i> 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 <i>NpFBA1</i> protein localized to the nucleus and cytoplasm. The expression of <i>NpFBA1</i> was induced by black shank pathogen (<i>Phytophthora parasitica</i> var. <i>nicotianae</i>) infection and treatment with salicylic acid (SA) and methyl jasmonate (MeJA). <i>NpFBA1</i>-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, <i>NpFBA1</i>-overexpressing lines were more susceptible to disease than wild-type (WT) plants. Further studies revealed that overexpression of <i>NpFBA1</i> significantly downregulated the expression of auxin response factors such as <i>NtARF3</i> and the lignin synthesis genes <i>NtPAL</i>, <i>NtC4H</i>, <i>NtCAD2</i>, and <i>NtCCR1</i> in the leaves. In conclusion, <i>NpFBA1</i> may play a key role in regulating leaf development and the response to pathogen infection.
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