AUTHOR=Liu Xiao-Ru , Pan Ting , Liang Wei-Qi , Gao Lan , Wang Xiao-Jing , Li Hong-Qing , Liang Shan 

TITLE=Overexpression of an Orchid (Dendrobium nobile) SOC1/TM3-Like Ortholog, DnAGL19, in Arabidopsis Regulates HOS1-FT Expression

JOURNAL=Frontiers in Plant Science

VOLUME=7

YEAR=2016

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2016.00099

DOI=10.3389/fpls.2016.00099

ISSN=1664-462X

ABSTRACT=<p>Flowering in the appropriate season is critical for successful reproduction in angiosperms. The orchid species, <italic>Dendrobium nobile</italic>, requires vernalization to achieve flowering in the spring, but the underlying regulatory network has not been identified to date. The MADS-box transcription factor <italic>DnAGL19</italic> was previously identified in a study of low-temperature treated <italic>D. nobile</italic> buds and was suggested to regulate vernalization-induced flowering. In this study, phylogenetic analysis of DnAGL9 and the MADS-box containing proteins showed that DnAGL19 is phylogenetically closely related to the SOC1-like protein from orchid <italic>Dendrobium</italic> Chao Parya Smile, DOSOC1. The orchid clade closed to but is not included into the SOC1-1/TM3 clades associated with either eudicots or monocots, suggesting that DnAGL19 is an SOC1-1/TM3-like ortholog. <italic>DnAGL19</italic> was found to be highly expressed in pseudobulbs, leaves, roots, and axillary buds but rarely in flowers, and to be substantially upregulated in axillary buds by prolonged low-temperature treatments. Overexpression of <italic>DnAGL19</italic> in <italic>Arabidopsis thaliana</italic> resulted in a small but significantly reduced time to bolting, suggesting that flowering time was slightly accelerated under normal growth conditions. Consistent with this, the <italic>A. thaliana APETELA1</italic> (<italic>AP1</italic>) gene was expressed at an earlier stage in transgenic lines than in wild type plants, while the <italic>FLOWERING LOCUS T</italic> (<italic>FT</italic>) gene was suppressed, suggesting that altered regulations on these transcription factors caused the weak promotion of flowering. <italic>HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENE 1</italic> (<italic>HOS1</italic>) was slightly activated under the same conditions, suggesting that the <italic>HOS1-FT</italic> module may be involved in the <italic>DnAGL19</italic>-related network. Under vernalization conditions, <italic>FT</italic> expression was significantly upregulated, whereas <italic>HOS1</italic> expression in the transgenic <italic>A. thaliana</italic> has a level similar to that in wild type. Taken together, these results suggest that <italic>DnAGL19</italic> controls the action of the <italic>HOS1-FT</italic> module depending on temperature cues, which could contribute to regulation of <italic>D. nobile</italic> flowering time. These data provide insights into how flowering is fine-tuned in <italic>D. nobile</italic> to acclimate the plant to seasonal changes in temperature.</p>