DE1与DLT互作介导油菜素内酯调控水稻茎节差异伸长的分子机制

Stem elongation is crucial for the establishment of shoot architecture and crop productivity. Brassinosteroid (BR) regulates the development of a set of internodes, mostly its dwarf mutants specially exhibit the shortest 2nd internode (dm) or the internodes below the 1st (d6) are short. But little is known about the molecular mechanism of this regulatory process. DLT is a positive regulator in BR signaling pathway, and all of dlt mutant internodes are relatively shorter. Previous study had reported that we screened two alleles of DLT enhancer dwarf mutant de1and de2 from dlt mutant library, and cloned the gene DE1 by MutMap and sequence analysis. de1 is manifested as d6 type dwarfing, with reduced sensitivity to BR; and the double mutant dde1 has the same dwarfing mode as de1. DE1 encodes a new homeo-box transcription factor, and DE1 can interact with DLT. These results strongly suggest that DE1-DLT complexes could regulate of the differential elongation of stem internode by BR signaling pathway. This project intends to further analysis the BR response in del mutant, and builds the BR genetic regulatory networks with de1 and other BR mutants, explores the cytological basis of different internode elongation, finally reveals how the interactions between DE1 and DLT control the stem development through BR signal pathway. This work may be beneficial for expanding our knowledge on the biological function of the HB family proteins in rice stem development, and providing new theoretical basis for improving the plant height traits in rice.

水稻茎节的有序伸长直接影响株型建立、穗部发育及抗倒伏能力，油菜素内酯(BR)在其中起着重要的调控作用。典型的BR缺陷突变体通常仅第二茎节或除第一茎节外下部茎节均特异缩短（d6型），但人们对这一调控过程的分子机制知之甚少。dlt是BR不敏感突变体且各茎节相对均匀缩短。前期工作中，我们筛选获得两个等位的dlt增强子矮杆突变体de1并克隆了基因。de1表现为d6型矮化，对BR敏感性降低,双突变体dde1与de1单突矮化模式相同，DE1编码同源框转录因子可与DLT直接互作。这些结果强烈暗示DE1和DLT形成复合体介导BR调控茎节的差异伸长。在此基础上，本项目拟进一步分析突变体对BR的响应，构建de1与BR相关突变体的遗传调控网络，探索茎节差异伸长的细胞学基础，解析DE1与DLT的互作对蛋白活性的影响，最终揭示二者如何介导BR信号调控水稻的茎节差异伸长，为理解并利用茎节发育过程调整株高性状奠定基础。

水稻茎节的有序伸长直接影响株型建立、穗部发育及抗倒伏能力，油菜素内酯(BR)在其中起着重要的调控作用。典型的BR缺陷突变体通常仅第二茎节（dm型）或除第一茎节外下部茎节均特异缩短（d6型），但人们对这一调控过程的分子机制知之甚少。本项目通过对已筛选的BR信号正调控子DLT的互作子OSH15进行深入研究，以阐明BR如何调控茎节发育的分子机制。结果发现，OSH15特异在茎节组织和穗部表达，相对于不同茎节，OSH15以底部茎节表达为主，而DLT主要在上部茎节表达；同时，在表型和分子水平上，OSH15与DLT共同影响大量下游基因在不同组织中呈现组织依赖性表达；进一步研究发现二者互作并共定位在细胞核，OSH15作为转录因子能够调控下游多个BR代谢和信号相关基因的表达，结合在BR信号关键基因BRI1的启动子上，促进该基因的表达，且DLT能够促进这一过程；最后，DLT与OSH15复合体能够介导水稻不同组织中BR含量的变化，影响不同组织的生长。本研究结果明确了BR在水稻茎节发育和籽粒发育途径中的作用，解析了DLT-OSH15通过调节BRI1的表达来介导BR调控差异水稻茎节伸长的分子机制，为提高水稻抗倒伏及产量提供理论基础和重要依据，同时BR兼具降低株高和增大籽粒的优势有望成为下一代分子设计育种的靶标。