苹果MbMAX2基因介导独脚金内酯信号在抑制腋芽萌发中的调控机制

Strigolactone (SL) has a specific inhibitory effect on the outgrowth of axillary buds in plant, but how it negatively regulates the auxin polar transport of axillary bud depending on the ubiquitin ligase gene MAX2, and the mechanism of inhibition of axillary bud outgrowth have been not reported. The applicant obtained a more-branching mutant of Malus baccata. Previous studies showed that the phenotype of the mutant plants might be related to the base variation of MbMAX2 gene, and the auxin polar transport played a key role in the outgrowth of apple axillary buds. Therefore, the more-branching mutant, its wild type and ‘Changfu No.2’ are used as materials in this study. The distribution of auxin and PIN1 protein in axillary buds will be analyzed by exogenous treatment. Based on the direct interaction of TOPP4 with PIN1 and promoting polar distribution of PIN1 in Arabidopsis, the interaction and relationship between MbMAX2 and MbTOPP4, MbTOPP4 and MbPIN1 will be verified by Y2H, BiFC, Co-IP and Western blot. The transgenic system of apple and Arabidopsis thaliana are used to verify the gene function of MbMAX2. Above these studies, it is will be helpful to resolve the mechanism of MbMAX2 mediating SL signal to inhibit apple branching, and enrich the theory of plant branching regulation.

独脚金内酯（SL）具有特异抑制植物腋芽萌发的作用，但其如何依赖泛素连接酶基因MAX2负向调控腋芽生长素极性运输，进而抑制萌芽的作用机制尚无报道。申请者获得了苹果属中一种山定子多分枝突变体，前期研究发现多分枝表型与其MbMAX2基因碱基变异可能相关，而且生长素极性运输在苹果腋芽萌发中作用关键。因此，本研究拟以该多分枝突变体及其野生型、‘长富2号’等为材料，利用外源SL等处理分析腋芽中生长素、PIN1蛋白的分布规律；以拟南芥中TOPP4直接互作PIN1并促进极性分布的关系为基础，利用Y2H、BiFC和Co-IP以及Western blot验证苹果MbMAX2与MbTOPP4、MbTOPP4与MbPIN1的互作与作用关系；利用苹果和拟南芥转基体系验证MbMAX2的基因功能。通过上述研究，有助于解析苹果MbMAX2响应SL信号抑制分枝的作用机制，并丰富植物分枝调控理论。

独脚金内酯（SL）具有特异抑制植物腋芽萌发的作用，但其如何依赖SL途径信号基因MAX2负向调控腋芽生长素极性运输，进而抑制萌芽的作用机制尚无报道。本研究以苹果中多分枝突变体及其野生型、‘长富2号’等为材料，利用外源独脚金内酯(GR24)、细胞分裂素(6-BA)、生长素极性运输抑制剂(NPA)等处理苹果腋芽，结果发现多分枝突变体表型与独角金内酯信号转导有关,且苹果腋芽中的生长素极性运输作用起着关键作用。MbMAX2基因异源转化拟南芥max2多分枝突变体，可以显著减少max2突变体的分枝数量，说明苹果MAX2基因具有抑制腋芽萌发的功能。酵母双杂交试验发现MbPIN1与MbTOPP4蛋白有直接互作关系，但MbMAX2与MbPIN1蛋白没有互作。结合MbPIN1转入拟南芥分枝增多、苹果腋芽萌发过程中PIN1表达上调与PIN1蛋白的极性分布增加，说明MbPIN1具有促进分枝的功能。进一步分析MbTOPP4转入拟南芥可促进分枝，且苹果腋芽萌发过程中MbTOPP4与MbPIN1表达协同上调，说明MbTOPP4可促进分枝。获得了MbMAX2、MbPIN1和MbTOPP4转苹果GL-3抗性株系。以上研究结果为系统解析苹果MAX2基因介导独角金内酯信号调控PIN1蛋白的分布机制提供了的重要依据。