Functional conservation and divergence of SEPALLATA-like genes in floral development in Cymbidium sinense

Abstract

Cymbidium sinense is one of the most important traditional Chinese Orchids due to its unique and highly ornamental floral organs. Although the ABCDE model for flower development is well-established in model plant species, the precise roles of these genes in C. sinense are not yet fully understood. In this study, four SEPALLATA-like genes were isolated and identified from C. sinense. CsSEP1 and CsSEP3 were grouped into the AGL9 clade, while CsSEP2 and CsSEP4 were included in the AGL2/3/4 clade. The expression pattern of CsSEP genes showed that they were significantly accumulated in reproductive tissues and expressed during flower bud development but only mildly detected or even undetected in vegetative organs. Subcellular localization revealed that CsSEP1 and CsSEP4 were localized to the nucleus, while CsSEP2 and CsSEP3 were located at the nuclear membrane. Promoter sequence analysis predicted that CsSEP genes contained a number of hormone response elements (HREs) and MADS-box binding sites. The early flowering phenotype observed in transgenic Arabidopsis plants expressing four CsSEP genes, along with the expression profiles of endogenous genes, such as SOC1, LFY, AG, FT, SEP3 and TCPs, in both transgenic Arabidopsis and C. sinense protoplasts, suggested that the CsSEP genes played a regulatory role in the flowering transition by influencing downstream genes related to flowering. However, only transgenic plants overexpressing CsSEP3 and CsSEP4 caused abnormal phenotypes of floral organs, while CsSEP1 and CsSEP2 had no effect on floral organs. Protein-protein interaction assays indicated that CsSEPs formed a protein complex with B-class CsAP3-2 and CsSOC1 proteins, affecting downstream genes to regulate floral organs and flowering time. Our findings highlighted both the functional conservation and divergence of SEPALLATA-like genes in C. sinense floral development. These results provided a valuable foundation for future studies of the molecular network underlying floral development in C. sinense.

Genome-wide identification and characterization of TCP gene family in Dendrobium nobile and their role in perianth development

“…Alternatively, MADS-specific binding sites (CArG boxes) are present in the majority of DnTCP putative promoters (Figure 5B), indicating that TCP and MADS-box may interact at the transcriptional level, with MADS-box acting as transcriptional repressors or activators of DnTCP genes (Lucibelli et al, 2021). Lin et al (2023) found that the transcriptional activation levels of AtTCP3 and AtTCP20 were an upregulated expression in transgenic lines that overexpressed CsSEP3 gene with curled leaf phenotypes. This result hints that the TCP gene can also act as a target gene of SEP3 in orchids, as has been observed in Arabidopsis and gerbera (Kaufmann et al, 2009;Zhao et al, 2020).…”

“…SEP-like acts as a binding agent for other MADS-box proteins ( Hugouvieux and Zubieta, 2018 ). Moreover, it is also necessary for the identity and meristem development of the perianth organs in orchids such as Dendrobium ( Yu and Goh, 2000 ), Habenaria radiata ( Mitoma and Kanno, 2018 ), and Cymbidium sinense ( Lin et al., 2023 ). A reasonable assumption is that the two Class I TCP proteins, DnTCP9 and DnTCP18, form dimers or heterodimers with DnSEP3; they might also form higher-order protein complexes with other types of MADS-box proteins ( Xu et al., 2006 ), providing a flexible mechanism for the regulation of perianth development in D. nobile .…”

Genetic Engineering and Genome Editing Advances to Enhance Floral Attributes in Ornamental Plants: An Update

“…Transgenic Arabidopsis expressing these four CsSEP genes exhibited the early flowering phenotype. Early flowering was associated with expression of endogenous flowering-related genes, suggesting that CsSEP regulates flowering by inducing downstream flowering genes [125]. Various genes that have been manipulated with genetic engineering to improve different floral traits are briefly listed in Table 2.…”