紫花苜蓿高迁移率族蛋白基因MsHMG-Y调控花期的功能分析

doi:10.3864/j.issn.0578-1752.2022.16.002

摘要/Abstract

摘要：

【目的】开花是植物营养生长转向生殖生长的重要标志,对植物的生物量有重要的影响。紫花苜蓿作为世界上最重要的饲草作物之一,其产量和品质与开花时间密切相关。紫花苜蓿的最佳刈割时期是初花期,此时产量和品质最佳。前期获得一个与花期相关的编码基因HMG-Y,通过分析其结构及表达模式,探究其在开花调控途径中的功能,为揭示开花调节机制提供理论基础。【方法】同源克隆MsHMG-Y,并对其进行多序列比对和进化树分析。利用qRT-PCR检测不同组织和不同开花时期该基因的表达水平;分析MsHMG-Y受光照、赤霉素（GA3）、水杨酸（SA）、茉莉酸甲酯（MeJA）诱导后的表达模式;观察过表达MsHMG-Y紫花苜蓿的表型,并分析开花促进因子与抑制因子的表达水平。【结果】MsHMG-Y与蒺藜苜蓿MtHMG-Y相似性最高,亲缘关系最近。组织特异性分析显示,MsHMG-Y在花、茎、叶中均有表达,其中,在父本和母本中均为花中表达量最高,叶中表达量最低;在早花表型父本的初花期表达量最高,在晚花表型母本的花芽分化期相对表达量最高。光周期分析表明,延长光照到16 h后,MsHMG-Y表达水平下调,延长光照到28 h后,MsHMG-Y表达水平持续低于对照组,说明该基因受光诱导后下调表达。外施50 μmol·L^-1 GA3、100 μmol·L^-1 SA、100 μmol·L^-1 MeJA后,与对照组相比,MsHMG-Y表达水平均上调,其中,GA3诱导1 h时表达量最高,为对照的3.5倍;SA诱导6 h时表达量最高,为对照的24倍;MeJA诱导3 h时表达量最高,为对照的11倍,说明该基因受3种激素诱导。表型观察发现,与对照相比,过表达MsHMG-Y紫花苜蓿开花较晚,促进开花相关基因的表达水平均下调,抑制开花相关基因的表达水平均上调,其中,表达量变化显著的有促进开花基因MsPHYA、MsGI和MsFTa1,分别降低了4.9、3.9和2.8倍,抑制开花基因MsTEM1和MsSVP的表达量分别提高了2.5和1.9倍。【结论】MsHMG-Y受光周期及外源激素GA3、SA和MeJA的诱导表达。MsHMG-Y对延迟苜蓿开花的调控机制有重要作用。

关键词: 紫花苜蓿, 高迁移率族-Y, 花期调控, 表达模式

Abstract:

【Objective】Flowering is an important signal indicating the transformation from vegetative growth to reproductive growth and has a significant effect on plant biomass. Alfalfa is one of the upmost forage crops worldwide, its yield and quality are closely related to flowering time. The optimum harvest time for alfalfa is during the early flowering stage, which could give the highest yield and the best quality. In the current study, an alfalfa flowering related gene, Medicago sativa High Mobility Group Y (MsHMG-Y), was cloned. The gene structure and expression pattern of MsHMG-Y were studied. Function of MsHMG-Y in alfalfa flowering regulation was analyzed. This work could provide theoretical support for mechanism study underlying flowering regulation. 【Method】MsHMG-Y was cloned by homology cloning strategy and the amino acid sequence was analyzed by multiple sequence alignment. The phylogenetic tree was also constructed. qRT-PCR analysis was used to detect the expression level of MsHMG-Y in different tissues and different flowering stages. The expression pattern of MsHMG-Y under light, gibberellin (GA3), salicylic acid (SA) or methyl jasmonate (MeJA) treatment were analyzed. The phenotype of MsHMG-Y-overexpressing alfalfa was analyzed, and the expression levels of flowering activators and suppressors were also analyzed. 【Result】Phylogenetic analysis showed that MsHMG-Y has the closest relationship with MtHMG-Y in Medicago truncatula. Spatial expression pattern analysis showed that MsHMG-Y was expressed in flowers, stems and leaves, with the highest expression level in flowers and the lowest expression level in leaves in both paternal and maternal alfalfa. In paternal alfalfa with early flowering phenotype, the expression level of MsHMG-Y was the highest at early flowering stage. The highest expression level of MsHMG-Y was detected at flower bud differentiation stage in maternal alfalfa with late flower phenotype. Photoperiod analysis showed that MsHMG-Y was down-regulated after 16-hour light treatment. After 28 hours of light treatment, the expression level of MsHMG-Y was continuously lower than that in the control group, indicating that MsHMG-Y was down-regulated after light treatment. After 50 μmol·L^-1 GA3, 100 μmol·L^-1 SA or 100 μmol·L^-1 MeJA treatment, the expression level of MsHMG-Y was up-regulated compared with the mock treatment. In detail, the expression level of MsHMG-Y was the highest at 1 h under GA3 treatment, which was 3.5 folds higher than control. Under SA treatment, the expression level of MsHMG-Y was the highest at 6 h, which was 24 folds higher than the mock treatment. The expression level of MsHMG-Y was the highest at 3 h under MeJA treatment, which was 11 folds higher than the control. These results indicated that the expression of MsHMG-Y was inducible by the above three hormones. MsHMG-Y-overexpressing alfalfa has late flowering phenotype. The expression levels of flowering activator genes were down-regulated in MsHMG-Y-overexpressing alfalfa, while the expression levels of flowering inhibitor genes were up-regulated. Among these genes, expression of flowering activator genes MsPHYA, MsGI and MsFTa1 was significantly down-regulated by 4.9 folds, 3.9 folds and 2.8 folds respectively, and the expression level of flowering inhibitor genes MsTEM and MsSVP was increased by 2.5 folds and 1.9 folds, respectively. 【Conclusion】The expression of MsHMG-Y is inducible by photoperiod and exogenous hormone treatment, including GA3, SA and MeJA. Overexpression of MsHMG-Y in alfalfa resulted in delayed flowering time. MsHMG-Y plays an important role in regulatory mechanism underlying late flowering in alfalfa.

Key words: alfalfa, High Mobility Group-Y, flowering regulation, expression pattern

张云秀,蒋旭,尉春雪,蒋学乾,卢栋宇,龙瑞才,杨青川,王珍,康俊梅. 紫花苜蓿高迁移率族蛋白基因MsHMG-Y调控花期的功能分析[J]. 中国农业科学, 2022, 55(16): 3082-3092.

ZHANG YunXiu,JIANG Xu,WEI ChunXue,JIANG XueQian,LU DongYu,LONG RuiCai,YANG QingChuan,WANG Zhen,KANG JunMei. The Functional Analysis of High Mobility Group MsHMG-Y Involved in Flowering Regulation in Medicago sativa L.[J]. Scientia Agricultura Sinica, 2022, 55(16): 3082-3092.

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顺式作用元件 Cis acting element	序列 Sequence (5′-3′)	物种 Species	数量 Number	功能 Function
TCA-element	CCATCTTTTT	烟草Nicotiana tabacum	1	参与水杨酸反应的顺式作用元件 Cis-acting element involved in salicylic acid responsiveness
TGACG-motif	TGACG	大麦Hordeum vulgare	1	参与茉莉酸甲酯反应的顺式作用元件 Cis-acting regulatory element involved in the MeJA-responsiveness
CGTCA-motif	CGTCA	大麦Hordeum vulgare	1	参与茉莉酸甲酯反应的顺式作用元件 Cis-acting regulatory element involved in the MeJA-responsiveness
GT1-motif	GGTTAA	拟南芥Arabidopsis thaliana	1	光响应元件 Light responsive element
TCT-motif	TCTTAC	拟南芥Arabidopsis thaliana	1	光响应元件 A light responsive element
G-box	CACGAC	玉米Zea mays	1	光响应顺式作用元件 Cis-acting regulatory element involved in light responsiveness