小麦细胞分裂素降解基因TaCKXx的功能研究与育种价值评估

CKX gene plays crucial role in maintaining CK levels and in the control of almost every aspect of plant growth and development. Manipulation of CKX gene holds great promise for improving a wide complex of agriculturally important traits in crop plants. In the previous study we found that TaCKXx-B1 were strongly associated with plant height in both an association mapping population of 167 diverse wheat accessions and in a linkage population, explaining 14-20% phenotype variation. Haplotype 1 associated with reduced plant height was positively selected during modern breeding improvement. In vivo expression assay showed that haplotypes responsible for higher- and lower-plant height reacted differently to GA-signal at the transcriptional level respectively. Our data provide evidence for crosstalk between GA and cytokinins connected by TaCKXx during wheat growth. Based on the above results, the objectives of this project include: 1) characterize the function of TaCKXx through transgene in wheat; 2) illustrate the mechanism of TaCKXx-B1 in GA-CK crosstalk and in modeling plant architecture; 3) make breeding value assessment for TaCKXx-B1 using near-isogenic lines or introgression lines screened with a functional marker of the gene developed by us, and put forward an effective utilization strategy of TaCKXx-B1 for wheat architecture improvement. The related work of this project has scientific and practical significance both for further insights into the complex hormone interaction network and for molecular breeding in bread wheat.

细胞分裂素降解酶（CKX）通过调控细胞分裂素水平影响到植物生长发育的诸多方面。小麦基因组中至少有7个CKX基因，但对其功能尚缺乏研究。项目申请者通过关联分析和连锁分析，发现TaCKXx-B1与小麦的株高变异关系密切，且在现代育种改良中经历了明显的正向选择，可能是一个在小麦育种上有重要价值的基因。表达分析证明TaCKXx-B1表达受GA信号下调，同时高矮秆单倍型间在转录水平上对GA信号反应存在明显差异。本研究拟在此基础之上，通过转基因了解TaCKXx的生物学功能；应用基因芯片技术和酵母单杂交系统探讨TaCKXx基因参与GA-CK互作和调控株型的作用机制；利用育种群体和回交导入系，评估基因的育种价值。本研究对于深入认识小麦中激素互作调控网络以及开展小麦分子育种均具有重要的科学和应用价值。

通过项目的实施，开展了小麦细胞分裂素降解基因TaCKXx的功能验证和育种价值评估。获得了TaCKXx基因过表达和下调表达的小麦转基因株系，其中7个过表达株系与野生型相比在成株期表现出矮或稍矮的表型，有6个RNAi干扰株系与野生型相比在成株期表现出高或稍高的表型，转基因株系的表达分析表明苗期根中TaCKXx基因表达量与A型-ARRs基因的表达呈显著负相关；同时过表达TaCKXx可以抑制赤霉素氧化基因GA2ox的表达，因此TaCKXx和GA2ox共同参与了赤霉素和细胞分裂素信号通路交叉互作进而影响植株形态建成。筛选获得了一对TaCKXx-B1基因位点的近等基因系，旱选10类型近等基因系的株高明显高于鲁麦14类型，同时在有效分蘖和穗粒数上差异显著。表达分析表明，两种基因型间TaCKXx-B1在成株期根和茎中的表达存在显著差异，同时，近等基因系苗期根部TaCKXx-B1基因表达量与A型ARR基因和GA2ox基因表达量均呈显著负相关。利用中国小麦微核心种质研究了TaCKXx-B1与主要矮秆基因的关系，Rht2对CKXx-B1具有较强的显性上位作用，Rht1对CKXx-B1具有较弱的显性上位作用，CKXx-B1对Rht8具有较弱的显性上位作用；主要矮秆基因降秆效应从大到小依次为：Rht2>Rht1>CKXx-B1>Rht8，CKXx-B1的降秆作用在7%-8%左右，CKXx-B1可以作为新的矮秆基因资源在育种中加以利用。