STF转录因子调控柳枝稷茎叶侧向生长的分子机制

STENOFOLIA (STF) is a WOX1-like gene in Medicago truncatula, which belongs to the WOX gene family. Overexpressing STF gene can promote the vascular development of leaves and stems in the monocots plant switchgrass, and improve the dry matter biomass of switchgrass. But no significant phenotype was detected in dicots’ plants. Since WOX1-like gene is specific in dicots, the regulatory mechanism of STF in monocots would be different from that in dicots. In this study, to clarify the mechanism, we will try to find target genes of STF and its interaction factors in switchgrass through transcriptome sequencing and yeast two hybrid library screening. Moreover, we will preliminarily explain the molecular mechanism on how STF promote the vascular development of leaves and stems by means of our efficient transformation technology of switchgrass. The candidate genes would be used to increase the biomass of energy grass, forage grass and other economic Graminae crops by regulating the organ outgrowth.

双子叶植物特异的WOX1类基因—STENOFOLIA（STF），在单子叶植物柳枝稷中过量表达，能够促进转基因植株的茎秆变粗和叶片变宽，最终提高柳枝稷的生物量。而在双子叶植物中过量表达STF，却不能对其表型产生显著影响。这一结果暗示在单子叶植物中可能存在一套特殊的分子机制，参与响应STF对茎叶侧向生长的调控。为了验证这一假设，本项目拟通过转录组测序和酵母双杂交筛库技术，从苜蓿STF基因过量表达的柳枝稷植株（STF-OE）中，筛选受STF调控的靶基因和与其相互作用的蛋白因子。在此基础上，借助于高效的柳枝稷基因转化技术，我们将解析部分STF靶基因和互作蛋白基因响应STF调控，促进茎叶侧向生长的分子机制。本项目发掘的基因新资源，今后有望作为植物器官侧向生长调控的新靶标，应用于能源草、牧草和其他重要经济作物生物量遗传改良的育种实践中。

本项目在禾本科植物柳枝稷中异源表达苜蓿STF转录因子，获得了茎秆增粗和叶片变宽的转基因植株。转录组数据显示，柳枝稷受STF转录因子调控的下游基因可能为细胞分裂素氧化酶基因PvCKX2。经体外试验验证，STF可直接结合PvCKX2基因启动子区，并抑制该基因的转录；PvCKX2表达受抑制进而会导致细胞数目增加，最终引起器官侧向生长。通过对柳枝稷PvCKX2基因进行遗传改良，证实了PvCKX2转基因柳枝稷会出现器官侧向生长的现象。同时，通过酵母文库筛选，获得了关键的STF候选互作因子PvWOX20；柳枝稷中过量表达PvWOX20也能显著促进器官侧向生长。本研究结果为禾本科草本植物的生物量改良提供了新的靶标。