禾本科作物中胚轴的伸长是重要农艺性状，与作物的深播和直播密切相关，是作物向高效节约型耕种模式转变的推动力，但其伸长的机制很不清楚。我们前期研究表明水稻油菜素甾醇(BRs)信号被抑制，中胚轴变短，反之，则伸长；而独脚金内酯(SLs)突变体的中胚轴显著伸长。我们还鉴定到调控水稻中胚轴伸长新基因RME1，分别与BR信号通路的负调节因子GSK2及SL信号通路的正调节因子D3互作，这些结果暗示RME1可能介导了BRs和SLs协同调控中胚轴伸长。因此，本项目将进一步研究BRs调控中胚轴伸长的细胞和分子基础；建立BRs和SLs通过RME1协同调控中胚轴伸长的细胞、遗传和分子机制。并对533份水稻微核心种质中胚轴伸长关联分析，鉴定并功能分析GSK2、D3和RME1的等位变异。本研究将揭示水稻中胚轴伸长的分子机制和调控网络，为促进作物的深播和直播的分子育种，推动高效、节能的耕种模式提供理论依据和基因资源。

Mesocotyl elongation, an important crop architecture trait, is necessary for crop deep-seeding and direct-seeding cultivation, and is also the impetus for less cost cultivation modes. But the underlying mechanism is still uncovered. In our previous research, we found that brassinosteroid (BR) signaling is necessary and positive for rice mesocotyl elongation; We identified a key gene RME1 (Rice Mesocotyl Elongation 1), which plays a positive role in promoting mesocotyl elongation. In addition, RME1 can interact with GSK2 (a GSK3-like kinase, functions as a negative regulator in rice BR signaling) and D3 (a subunit of the Skp–Cullin–F-box (SCF) E3 ubiquitin ligase complex, acting as a positive regulator in rice strigolactone (SL) signaling), which indicates that RME1 might play a key role in SLs/BRs-regulated rice mesocotyl elongation in darkness. In this project, we'll reveal the cytology structures and the mechanism under BR-regulating rice mesocotyl elongation, and establish the regulatory networks under the mesocotyl elongation among the BR/GSK2, SL/D3, and RME1. In addition, we will make the genetic diversity and association analysis to identify the favorable alleles of the genes (GSK3, D3, and RME1) for rice mesocotyl genetic improvement using 533 rice mini-core accessions. The completion of this research will give us theoretical basis to make the ideal mesocotyl architecture for deep seeding and direct seeding.