Comprehensive transcriptomic analysis provides new insights into the mechanism of ray floret morphogenesis in chrysanthemum

Abstract

Background The ray floret shapes referred to as petal types on the chrysanthemum (Chrysanthemum × morifolium Ramat.) capitulum is extremely abundant, which is one of the most important ornamental traits of chrysanthemum. However, the regulatory mechanisms of different ray floret shapes are still unknown. C. vestitum is a major origin species of cultivated chrysanthemum and has flat, spoon, and tubular type of ray florets which are the three basic petal types of chrysanthemum. Therefore, it is an ideal model material for studying ray floret morphogenesis in chrysanthemum. Here, using morphological, gene expression and transcriptomic analyses of different ray floret types of C. vestitum, we explored the developmental processes and underlying regulatory networks of ray florets. Results The formation of the flat type was due to stagnation of its dorsal petal primordium, while the petal primordium of the tubular type had an intact ring shape. Morphological differences between the two ray floret types occurred during the initial stage with vigorous cell division. Analysis of genes related to flower development showed that CYCLOIDEA genes, including CYC2b, CYC2d, CYC2e, and CYC2f, were differentially expressed in different ray floret types, while the transcriptional levels of others, such as MADS-box genes, were not significantly different. Hormone-related genes, including SMALL AUXIN UPREGULATED RNA (SAUR), GRETCHEN HAGEN3 (GH3), GIBBERELLIN 2-BETA-DIOXYGENASE 1 (GA2OX1) and APETALA2/ETHYLENE RESPONSIVE FACTOR (AP2/ERF), were identified from 1532 differentially expressed genes (DEGs) in pairwise comparisons among the flat, spoon, and tubular types, with significantly higher expression in the tubular type than that in the flat type and potential involvement in the morphogenesis of different ray floret types. Conclusions Our findings, together with the gene interactional relationships reported for Arabidopsis thaliana, suggest that hormone-related genes are highly expressed in the tubular type, promoting petal cell division and leading to the formation of a complete ring of the petal primordium. These results provide novel insights into the morphological variation of ray floret of chrysanthemum.

Ray flower initiation in the Helianthus radula inflorescence is influenced by a functional allele of the HrCYC2c gene

“…Moreover, recent data collected in Chrysanthemum × morifolium Ramat. showed that the involvement of a different set of hormone‐related genes can be identified between ray and disk flowers (Pu et al, 2020). Overall, these data would indicate that in Asteraceae a complex regulatory network controls the different forms of inflorescences.…”

Sepal Identity of the Pappus and Floral Organ Development in the Common Dandelion (Taraxacum officinale; Asteraceae)

“…To decide on pappus–sepal homology, we first observed the floral development of dandelion micromorphologically ( Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 and Figure 6 ; Supplementary Figures S1–S5 and Video’s SV1 and SV2 ) and defined the different stages of floral initiation, floral maturation, and seed formation ( Table 1 ). Well-defined stages of floral ontogenesis are available for some model species, particularly Arabidopsis [ 63 ], but in the Asteraceae the main focus has been on the inflorescence and not florets development, for instance in Gerbera [ 64 ], with additional floral initiation stages in [ 65 ], and recent studies in Chrysanthemum [ 66 ], lettuce [ 53 ], and the rubber dandelion ( T. kok-saghyz ) [ 67 ]. Our study concerns the floret development only, starting with the floral primordium as stage 1 , and is aimed as a reference for dandelions and, where possible, other Asteraceae.…”

Comparison of chrysanthemum flowers grown under hydroponic and soil-based systems: yield and transcriptome analysis

“…In this work (Fig. 9 ), ERF, Trihelix, WRKY and C3H family members were identified in chrysanthemum, and were upregulated during chrysanthemum flower bud differentiation or development [ 35 – 41 ]. This implies that these genes may be involved in flower developmental processes, and these TFs should be further studied in chrysanthemum.…”

“…Flower bud differentiation or development are important tissue to chrysanthemum for tea. Flowering is a complex process controlled by gene expression and phytohormones [33][34][35][36][37][38][39][40]. In chrysanthemum, important transcription factors (TFs) involved in flower development have been isolated and analyzed, including those encoded by the homologs of the Arabidopsis genes APETALA1, SEPALLATA3, FRUITFULL, LEAFY, APETALA2,TEOSINTE BRANCHED1/ CYCLOIDEA/PROLIFERATING CELL FACTOR20, and CYCLOIDEA2c, as well as many genes encoding MADSbox and WUSCHEL (WUS)-like proteins [33][34][35][36][37][38][39][40].…”