Abstract: Flowering is a critical physiological process in the plant life cycle, and the photoperiod plays a key regulatory role in determining the timing of flowering. Members of the basic Helix-Loop-Helix （bHLH） gene family are crucial participants in the photoperiodic regulation of flowering pathways. To explore the role of bHLH family members in the regulation of flowering time in alfalfa（Medicago sativa L.）, the gene MsCIB2, located in subfamily 18, was cloned. The full length of MsCIB2 is 1533 bp, encoding 511 amino acids. Tissue-specific expression analysis revealed that the expression levels of MsCIB2 ranked from high to low as follows： flowers>mature stems>new stems>mature leaves>new leaves. During different flower development stages, MsCIB2 expression was significantly higher in late-flowering plants compared to early-flowering plants, with the highest expression observed at the full-bloom stage in late-flowering plants. Quantitative RT-PCR analysis showed that MsCIB2 was induced under long-day （LD） conditions but maintained low expression levels under short-day （SD） conditions. Additionally, MsCIB2 expression was induced by plant hormones such as IAA, MeJA, SA, and ABA but was suppressed under drought and high-salinity stress. Overexpression of MsCIB2 in Arabidopsis thaliana delayed flowering by 2-4 days under LD conditions and significantly delayed flowering by 12-14 days under SD conditions. Furthermore, the overexpression of MsCIB2 slightly increased vegetative biomass, suggesting that MsCIB2 plays an important role in the physiological regulation of flowering via the photoperiodic pathway.

Key words: Alfalfa, MsCIB2, Expression mode, Flowering time

摘要： 开花是植物生命周期的重要生理过程,而光周期对植物开花时间起重要的调控作用。basic Helix-Loop-Helix（bHLH）基因家族成员在光周期调控开花途径中发挥着重要作用。为了探究紫花苜蓿（Medicago sativa L.）bHLH基因家族成员在花期调控中的功能,克隆了位于第18亚族的MsCIB2基因,该基因全长1533 bp,编码511个氨基酸；组织差异性分析显示,MsCIB2在植物各组织的表达量从高到低排序为：花>老茎>幼茎>老叶>幼叶；花不同发育时期表达分析显示,MsCIB2在晚花材料中的表达水平显著比早花材料高,其中在晚花材料的盛花期表达量最高；qRT-PCR分析显示,MsCIB2在LD下被诱导表达,SD下维持在较低的表达水平,同时MsCIB2也受植物激素（IAA,MeJA,SA和ABA）诱导表达,干旱和高盐胁迫下则被抑制表达。过表达MsCIB2拟南芥（Arabidopsis thaliana L.）在长日照条件下推迟开花2~4 d,而在短日照条件下显著延迟开花12~14 d,同时一定程度上增加了植物营养体的生物量,暗示MsCIB2在植物光周期途径调控开花的生理过程中发挥重要作用。

关键词: 紫花苜蓿, MsCIB2, 表达模式, 开花时间