Identification and characterization of two APETALA2 homolog genes in lotus (Nelumbo nucifera) involved in sepal and petal development

BackgroundLotus (Nelumbo nucifera) is a significant aquatic ornamental genus widely utilized in horticulture for its decorative, culinary, medicinal, and other practical uses. It presents a variety of flower shapes, including few-petalled, semi-double-petalled, double-petalled and thousand-petalled flowers, making it an ideal candidate for studying the flower development of aquatic plants. However, the molecular mechanism of floral development in lotus remains elusive.ResultsIn this study, two APETALA2 (AP2) homologues, NnAP2a and NnAP2b, were identified in lotus. Interestingly, both NnAP2a and NnAP2b proteins contained two conserved AP2 domains and were verified to be located primarily in the nucleus. Both NnAP2a and NnAP2b showed high expression levels in the floral buds and petals. Ectopic expression of NnAP2a and NnAP2b in Arabidopsis led to an increase in the number of petals and sepals compared to the wild type (WT). Meanwhile, each of the two NnAP2 genes was able to rescue the sepal and petal defective phenotype of the ap2-6 mutant in Arabidopsis. Furthermore, protein-protein interaction assays indicated that NnAP2s could form a protein complex with other proteins involved in floral organ development, such as AP3, PISTILLATA (PI), and SEPALLATA3 (SEP3).ConclusionsThese results suggest that NnAP2s could influence sepal and petal development in N. nucifera. Our findings not only provide some insights into molecular mechanism underlying sepal and petal development and formation of lotus, but also might help its breeding in improving flower morphology.