Isolation and functional characterization of two SOC1-like genes in floral organ development of Lonicera macranthoides

Overexpression of either LmSOC1-1 or LmSOC1-2 in Arabidopsis thaliana promoted earlier flowering and extended the bud stage. It also led to alterations in floral organ morphology, such as the failure of the corolla to unfold or the development of a filamentous corolla.

The SUPPRESSOR OF OVEREXPRESSION OF CO 1 (SOC1) is a key integrator of flowering signals in plants. It plays essential roles in floral meristem identity, the regulation of flowering time, and floral organ morphogenesis across diverse plant species. In this study, two SOC1 homologs, designated LmSOC1-1 and LmSOC1-2, were cloned from Lonicera macranthoides. Bioinformatics analysis confirmed that both genes, as members of the MADS-box gene family, harbor a highly conserved MADS domain, yet exhibit divergence. Expression profiling showed that these two genes were highly expressed in vegetative tissues (stems and leaves) but exhibited low expression in floral buds. Moreover, they differed in expression dynamics during flower bud development and in promoter-binding activity. Yeast two-hybrid assays demonstrated protein–protein interactions: LmSOC1-1 with LmSVP1 and LmSVP2, and LmSOC1-2 with LmAP1. Both genes promoted flowering when heterologously overexpressed in Arabidopsis, concomitantly affecting rosette leaf number, and this pro-flowering function was further substantiated by the successful complementation of the soc1 mutant. Additionally, LmSOC1-1 overexpression prolonged the flower bud stage. Overexpression lines also exhibited altered floral organ phenotypes: non-unfolding corolla in LmSOC1-1 lines and filamentous corolla in LmSOC1-2 lines. Consistent with a role in flowering regulation, overexpression of LmSOC1s upregulated the expression of several Arabidopsis flowering-related genes, including AtAP1, AtAGL24, AtFUL, and AtLFY. These results suggest that LmSOC1-1 and LmSOC1-2 play important but partially distinct roles in regulating flowering time and floral organ morphology in L. macranthoides.