柴胡Aux/IAA基因对侧根形成的影响

Root branching is very important for yield, medicinal ingredients content and commercial quality to Bupleurum species, because their roots are used as herbal drugs. Previous studies of root branching in Arabidopsis, rice, and maize indicated that Aux/IAA genes can regulate polar auxin transport to controls prebranch site formation and lateral root initiation. In the present project, root branching and histological analyses will be performed among two commercial varieties of ChuanbeichaiNo. 1 (Bupleurum chinense DC) and Zhonghongchai No. 1 (B. scorzonerifolium Willd). The expression patterns of Aux/IAA genes in different tissues, and the Aux/IAA genes expression change associated with exogenous IAA treatment will be analyzed to identify the key genes can regulate root branching in Bupleurum. Arabidopsis transformation and gene overexpression in Zhonghongchai No. 1 will be conducted to verify the key role of candidate genes. In addition, the promoters of these Aux/IAA genes will be cloned and their tissue specificity will be analyzed in our study. This study will advance our understanding about histological and molecular mechanisms, and provide theoretical basis for root branching improvement in Bupleurum.

柴胡(Bupleurum spp.)以根入药，其侧根分支多少与柴胡产量、药效成分含量及商品性密切相关。对拟南芥、水稻及玉米等植物研究表明Aux/IAA基因通过调节生长素极性运输对植物侧根位点发生位置及侧根初始化起主要调控作用。本研究拟分析柴胡不同基因型（北柴胡品种川北柴1号及狭叶柴胡品种中红柴1号）的根系形态差异及其组织结构基础，通过组织特异性表达分析及外施IAA对Aux/IAA基因的应答模式，筛选并克隆影响柴胡侧根形成的Aux/IAA关键基因。通过转化拟南芥突变体及在中红柴1号中超量表达以分析Aux/IAA基因在柴胡中的生物学功能；克隆Aux/IAA基因启动子，并分析该启动子的组织特异性。本研究将揭示柴胡侧根分支差异的结构及分子基础，为柴胡根系改良提供理论依据。

柴胡侧根分支多少是决定其柴胡皂苷产量和品质的关键因素之一。柴胡皂苷主要集中于根部皮层组织。多支根型基因型柴胡皮层组织相对较多，有效成分含量也较高，有益于柴胡皂苷提取加工。单支根型柴胡侧根少，但根条粗长，利于传统柴胡饮片加工。本项目发现狭叶柴胡新品种川红柴1号侧根原基发育过程与北柴胡新品种川北柴1号基本类似，但无内皮层细胞的参与。外施生长素和钙离子对柴胡根系发育起促进作用，而生长素抑制剂（TIBA）和钙离子螯合剂（EDTA）对柴胡根系发育起抑制作用；筛选出稳定的内参基因ADF7、ADF5及ADF1b，以提高目的基因表达分析的精确性及可信度；优化并构建了稳定的北柴胡可再生体系及遗传转化体系，进一步拓展了北柴胡分子遗传研究平台；通过转录组分析生长素合成、运输及调控侧根原基的调控通路基因表达变化；分离出18个AUX/IAA家族成员，通过基因型、不同组织及外施生长素的应答机制分析表达模式分析；利用新构建的北柴胡遗传转化体系发现，超表达BcIAA13植株侧根显著高于野生型植株。项目结果有助于阐释北柴胡及狭叶柴胡差异根系构型的分子机理，为柴胡定向根系改良提供理论依据。