StOSD1/UVI4 is crucial for accurate mitotic progression and the maintenance of leaf morphology in potato

Accurate cell cycle progression is essential for plant growth and development. UVI4(UV-B-insensitive 4) and its homologue OSD1(Omission of the Second Division) function as negative regulators of the anaphase-promoting complex/cyclosome (APC/C) and are critical for cell cycle regulation in plants. In potato, UVI4 and OSD1 have a single homologue, StOSD1/UVI4, and the role of one copy of this gene in cell cycle regulation is largely unknown. We showed that mutation of StOSD1/UVI4 in potato resulted in a shorter plant height and a variegated leaf phenotype characterized by mosaic areas with dark green and light green colours. The mutant plants presented altered chloroplast distribution and decreased fluorescence signal in palisade cells within the light-green sectors, accompanied by a significant reduction in total chlorophyll content. Transcriptome analysis revealed the downregulation of genes associated with chlorophyll biosynthesis in the mutant. Paraffin sectioning revealed increased cell volume in the light green regions. Ploidy analysis via 5S rDNA fluorescence in situ hybridization (FISH) demonstrated that the StOSD1/UVI4 mutation induced endomitosis in the palisade cells in the light green sectors. Further ploidy determination in leaf cells via 26S rDNA and 5S rDNA FISH revealed that the StOSD1/UVI4 mutation led to a replication pattern combining incomplete replication with endomitosis. These findings indicate that the StOSD1/UVI4 mutation impairs chloroplast distribution and function in potato and triggers endomitosis. Additionally, the number of nonglandular trichomes on the leaf epidermis decreased, and the second division at meiosis was skipped in the StOSD1/UVI4 mutant. Our findings establish a novel link between endomitosis and chlorophyll accumulation in plants. Additionally, we reveal roles for StOSD1/UVI4 in plant morphology (influencing trichome density) and meiosis (ensuring the second division). Collectively, these findings underscore a new role for StOSD1/UVI4 in regulating mitosis, plant morphology, and leaf development in potato.