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Plants of the genus Narcissus are well-known for their characteristic corona morphology, which structural origins have been a bone of contention among scholars. With “Jinzhanyintai” (JZ) and “Yulinglong” (YLL)—two major close-originated cultivars of Chinese narcissus (Narcissus tazetta L. var. chinensis Roem)—as materials, anatomic observation was made on floral organs during corona morphogenesis by dissection with hands under a stereomicroscope, paraffin section, scanning electron microscopy, and high-resolution X-ray tomography. It was uncovered that corona primordia of both cultivars appeared following the end of the differentiation of other floral organs, with differentiation sites located at the inner wall of the juncture of the base of tepals and the upper margin of the hypanthium. Affected by staminal filaments, the corona primordia of JZ experienced a three-stage differentiation process, namely blockage from the second whorl of stamens, blockage from the first whorl of stamens, and healing of corona primordia. However, the expanded spatial structure of the first whorl of petal-like stamens blocked the path of differentiation of YLL corona primordia, giving rise to slow differentiation of the corona primordia at the base of the first whorl of petal-like stamens and malformed differentiation of the corona primordia in the interval between the two whorls of petal-like stamens. Thus, a fragmented structure consisting of typical and fragmented coronas was formed. Furthermore, petal-like stamens of YLL in the lower part had a corona-like morphology. The spatio-temporal specificity of corona differentiation convincingly demonstrates that the corona is a structure independent of and different from the typical four whorls of floral organs, but also highly correlated with stamen. Full article

Male sterility caused by stamen petalody is a key factor for a low fruit set rate and a low yield of Camellia oleifera but can serve as a useful genetic tool because it eliminates the need for artificial emasculation. However, its molecular regulation mechanism still remains unclear. In this study, transcriptome was sequenced and analyzed on two types of bud materials, stamen petalody mutants and normal materials, at six stages of stamen development based on integrated single-molecule real-time (SMRT) technology with unique molecular identifiers (UMI) and RNA-seq technology to identify the hub genes responsible for stamen petalody in C. oleifera. The results show that a large number of alternative splicing events were identified in the transcriptome. A co-expression network analysis of MADSs and all the differentially expressed genes between the mutant stamens and the normal materials showed that four MADS transcription factor genes, CoSEP3.1, CoAGL6, CoSEP3.2, and CoAP3, were predicted to be the hub genes responsible for stamen petalody. Among these four, the expression patterns of CoAGL6 and CoSEP3.2 were consistently high in the mutant samples, but relatively low in the normal samples at six stages, while the patterns of CoSEP3.1 and CoAP3 were initially low in mutants and then were upregulated during development but remained relatively high in the normal materials. Furthermore, the genes with high connectivity to the hub genes showed significantly different expression patterns between the mutant stamens and the normal materials at different stages. qRT-PCR results showed a similar expression pattern of the hub genes in the RNA-seq. These results lay a solid foundation for the directive breeding of C. oleifera varieties and provide references for the genetic breeding of ornamental Camellia varieties. Full article