Location: Crops Pathology and Genetics ResearchTitle: Control of chrysanthemum flowering through integration with an aging pathway
|WEI, QIAN - China Agricultural University|
|MA, CHAO - China Agricultural University|
|XU, YANJIE - China Agricultural University|
|WANG, TIANLE - China Agricultural University|
|CHEN, YIYU - China Agricultural University|
|LU, JING - China Agricultural University|
|ZHANG, LILI - China Agricultural University|
|HONG, BO - China Agricultural University|
|GAO, JUNPING - China Agricultural University|
Submitted to: Nature Communications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/24/2017
Publication Date: 10/10/2017
Citation: Wei, Q., Ma, C., Xu, Y., Wang, T., Chen, Y., Lu, J., Zhang, L., Jiang, C., Hong, B., Gao, J. 2017. Control of chrysanthemum flowering through integration with an aging pathway. Nature Communications. 8:829. https://doi.org/10.1038/s41467-017-00812-0.
Interpretive Summary: Flowering at the appropriate time is critical for optimal sexual reproductive success, and is determined by a complex interplay of environmental cues and internal signals. Angiosperms have evolved several mechanisms to coordinately regulate floral transition, including signaling controlled by photoperiod and vernalization, as well as by the gibberellin and aging pathways. These flowering pathways converge on a common set of downstream flowering time integrators. Among these flowering pathways, the aging pathway provides an endogenous developmental cue that prevents flowering during the juvenile phase, and ensures flowering during the adult phase, even in the absence of exogenous inductive factors. A microRNA (miRNA), miR156, and its targets, SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) genes, have been identified as key components of the aging pathway that underlies the transition from the juvenile-to-adult phases, and that promotes flowering. However, while some components of the complex aging pathway regulatory system have been elucidated, the upstream transcription effectors that modulate miR156 levels are still largely unknown. Previous studies have demonstrated that flowering time, abiotic stress tolerance, and various aspects of plant development are regulated by nuclear factor Y (NF-Y) proteins. NF-Y proteins comprise NF-YA, NF-YB, and NF-YC subunits that form conserved heterotrimeric transcription factor complexes in all higher eukaryotes. NF-Y complexes bind to the CCAAT motif in the promoters of many genes. In plants, each NF-Y subunit is encoded by 8–39 genes, so there are potentially thousands of unique heterotrimeric NF-Y complexes that may enable the specific regulation of a variety of transcriptional profiles. However, less is known about the involvement of NF-Y proteins in the aging pathway. Chrysanthemum (Chrysanthemum morifolium) is a typical obligate short day (SD) herbaceous perennial species, and has provided a useful model to study the role of day length in the transition from vegetative to inflorescence meristem identity. Studies of chrysanthemum flowering to date have mainly focused on the significance and molecular regulation of the photoperiod pathways. It has been shown that the juvenile-to-adult transition during vegetative growth, which is required for chrysanthemum flowering, must occur before any response to SD period can take place. However, little is known about the mechanism that controls the juvenile-to-adult transition in chrysanthemum. Here we report that the chrysanthemum nuclear factor CmNF-YB8 modulates flowering time by mediating the juvenile-to-adult transition. Further transcriptome analysis reveals that CmNF-YB8 regulates the expression of genes related to aging pathway. Notably, CmNF-YB8 is shown to bind to the promoter of the cmo-MIR156 gene. Ectopic expression of cmo-miR156 restores the early flowering phenotype caused by CmNF-YB8 silencing. Our findings uncover that CmNF-YB8 is a critical regulator of age-dependent flowering time by directly regulating cmo-MIR156 expression in chrysanthemum.
Technical Abstract: Age, as a threshold of floral competence acquisition, prevents precocious flowering when there is insufficient biomass, and ensures flowering independent of environmental conditions; however, the underlying regulatory mechanisms are largely unknown. In this study, silencing the expression of a nuclear factor gene, CmNF-YB8, from the short day plant chrysanthemum (Chrysanthemum morifolium), results in precocious transition from juvenile to adult, as well as early flowering, regardless of day length conditions. The expression of SQUAMOSA PROMOTER BINDING-LIKE (SPL) family members, SPL3, SPL5, and SPL9, is upregulated in CmNFYB8-RNAi plants, while expression of the microRNA, cmo-MIR156, is downregulated. In addition, CmNF-YB8 is shown to bind to the promoter of the cmo-MIR156 gene. Ectopic expression of cmo-miR156, using a virus-based microRNA expression system, restores the early flowering phenotype caused by CmNF-YB8 silencing. These results show that CmNFYB8 influences flowering time through directly regulating the expression of cmo-MIR156 in the aging pathway.