独脚金内酯信号通路D53-like SMXLs下游转录因子的鉴定与功能分析

Shoot branching is a major determinant of plant architecture. Recently, strigolactones (SLs) have been identified as a new type of hormones that can inhibit lateral bud outgrowth and play critical roles in shoot branching regulation. In rice (Oryza sativa), SL signaling requires the degradation of DWARF53 (D53), mediated by a complex including DWARF14 (D14) and DWARF3 (D3). In Arabidopsis thaliana the SL-dependent regulation of shoot branching and leaf shape require three D53-like proteins, SUPPRESSOR OF MORE AXILLARY GROWTH2-LIKE6 (SMXL6), SMXL7 and SMXL8. The smxl6 smxl7 smxl8 triple mutant suppresses the highly branched phenotypes of more axillary growth 2 (max2) and the SL-deficient mutant more axillary growth 3 (max3). Overexpression of a mutant form of SMXL6 that is resistant to SL-induced ubiquitination and degradation enhances shoot branching. Exogenous application of the SL analog rac-GR24 causes ubiquitination and degradation of SMXL6, 7 and 8, which is mediated by a complex including D14 and MAX2. D53-like SMXLs exhibit TPR2-dependent transcriptional repression activity and repress the expression of BRANCHED1 (BRC1). However, the molecular mechanism underlying transcriptional repression activity of D53-like SMXLs remains unclear. Recently, we have identified the D53-like SMXLs Interacting Transcription Factor 1 (DSIF1) in Arabidopsis through yeast two hybrid assay of a transcription factor library. DSIF1 interacted with D53-like SMXLs in vitro and in vivo. In transcriptional activity assays using Arabidopsis protoplasts, DSIF1 showed strong transactivation activity and D53-like SMXLs repressed its transactivation activity. The phenotypes of transgenic plants overexpressing DSIF1 or DSIF1-SRDX indicated that DSIF1 functions as a negative regulator of shoot branching. These results suggested that DSIF1 may act downstream of D53-like SMXLs to activate SL signaling pathway. This project intends to carry out an extensive study on DSIF1 function utilizing multiple discipline approaches, for example genome-editing, genetic analysis, Chromatin Immunoprecipitation-Sequencing (ChIP-Seq) and RNA-Seq analyses, aiming to clarify the role of DSIF1 in SL signaling transduction, to identify early SL responsive genes acting downstream of DSIF1, and to elucidate the molecular mechanism underlying shoot branching regulation through SL signaling pathway.

分枝是决定株型发育的主要因素，独脚金内酯作为一种新的植物激素通过抑制侧芽的伸长在分枝发育中发挥重要作用。DWARF53 (D53)和D53-like SMXLs是水稻和拟南芥独脚金内酯信号通路的关键抑制因子。我们鉴定了与D53-like SMXLs互作的转录因子D53-like SMXLs Interacting Transcription Factor 1 (DSIF1)，发现DSIF1与D53-like SMXLs在体外和体内互作，DSIF1的转录激活活性受到D53-like SMXLs的抑制，DSIF1负调控分枝数目，暗示DSIF1可能在D53-like SMXLs下游激活独脚金内酯信号转导。本项目拟对DSIF1开展深入研究，明确DSIF1在独脚金内酯信号通路中的位置，鉴定位于DSIF1下游参与分枝调控的独脚金内酯早期响应基因，解析独脚金内酯调控植物分枝发育的分子机制。