AUTHOR=Lin Zeng-Yu , Zhu Gen-Fa , Lu Chu-Qiao , Gao Jie , Li Jie , Xie Qi , Wei Yong-Lu , Jin Jian-Peng , Wang Feng-Lan , Yang Feng-Xi 

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

JOURNAL=Frontiers in Plant Science

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2023.1209834

DOI=10.3389/fpls.2023.1209834

ISSN=1664-462X

ABSTRACT=<p><italic>Cymbidium sinense</italic> 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 <italic>C. sinense</italic> are not yet fully understood. In this study, four <italic>SEPALLATA</italic>-like genes were isolated and identified from <italic>C. sinense</italic>. <italic>CsSEP1</italic> and <italic>CsSEP3</italic> were grouped into the <italic>AGL9</italic> clade, while <italic>CsSEP2</italic> and <italic>CsSEP4</italic> were included in the <italic>AGL2/3/4</italic> clade. The expression pattern of <italic>CsSEP</italic> 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 <italic>CsSEP1</italic> and <italic>CsSEP4</italic> were localized to the nucleus, while <italic>CsSEP2</italic> and <italic>CsSEP3</italic> were located at the nuclear membrane. Promoter sequence analysis predicted that <italic>CsSEP</italic> 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 <italic>CsSEP</italic> genes, along with the expression profiles of endogenous genes, such as <italic>SOC1</italic>, <italic>LFY</italic>, <italic>AG</italic>, <italic>FT</italic>, <italic>SEP3</italic> and <italic>TCPs</italic>, in both transgenic Arabidopsis and <italic>C. sinense</italic> protoplasts, suggested that the <italic>CsSEP</italic> genes played a regulatory role in the flowering transition by influencing downstream genes related to flowering. However, only transgenic plants overexpressing <italic>CsSEP3</italic> and <italic>CsSEP4</italic> caused abnormal phenotypes of floral organs, while <italic>CsSEP1</italic> and <italic>CsSEP2</italic> 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 <italic>SEPALLATA</italic>-like genes in <italic>C. sinense</italic> floral development. These results provided a valuable foundation for future studies of the molecular network underlying floral development in <italic>C. sinense</italic>.</p>