Chen Xiao, Liao Dehua, Yang Xiaofeng, Ji Minjie, Wang Shuangshuang, Gu Mian, Chen Aiqun, Xu Guohua
State Key Laboratory of Crop Genetics and Germplasm Enhancement, College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing, China.
MOA Key Laboratory of Plant Nutrition and Fertilization in Lower-Middle Reaches of the Yangtze River, Nanjing Agricultural University, Nanjing, China.
Plant Cell Physiol. 2017 Apr 1;58(4):770-778. doi: 10.1093/pcp/pcx013.
Auxin is well known to be a key regulator that acts in almost all physiological processes during plant growth, and in interactions between plants and microbes. However, to date, the regulatory mechanisms underlying auxin-mediated plant-arbuscular mycorrhizal (AM) fungi symbiosis have not been well deciphered. Previously we identified a GH3 gene, SlGH3.4, strongly responsive to both auxin induction and mycorrhizal symbiosis. Here, we reported a refined dissection of the SlGH3.4 promoter activity using the β-glucuronidase (GUS) reporter. The SlGH3.4 promoter could drive GUS expression strongly in mycorrhizal roots of soybean and rice plants, and in IAA-treated soybean roots, but not in IAA-treated rice roots. A promoter deletion assay revealed three cis-acting motifs, i.e. the auxin-responsive element, AuxRE, and two newly identified motifs named MYCRS1 and MYCRS2, involved in the activation of auxin- and AM-mediated expression of SlGH3.4. Deletion of the AuxRE from the SlGH3.4 promoter caused almost complete abolition of GUS staining in response to external IAA induction. Seven repeats of AuxRE fused to the Cauliflower mosaic virus (CaMV) 35S minimal promoter could direct GUS expression in both IAA-treated and AM fungal-colonized roots of tobacco plants. Four repeats of MYCRS1 or MYCRS2 fused to the CaMV35S minimal promoter was sufficient to drive GUS expression in arbuscule-containing cells, but not in IAA-treated tobacco roots. In summary, our results offer new insights into the molecular mechanisms underlying the potential cross-talk between the auxin and the AM regulatory pathways in modulating the expression of AM-responsive GH3 genes in diverse mycorrhizal plants.
生长素是一种关键调节因子，在植物生长的几乎所有生理过程以及植物与微生物的相互作用中都发挥作用。然而，迄今为止，生长素介导的植物与丛枝菌根（AM）真菌共生的调控机制尚未得到很好的解析。此前我们鉴定出一个GH3基因SlGH3.4，它对生长素诱导和菌根共生均有强烈响应。在此，我们报道了使用β-葡萄糖醛酸酶（GUS）报告基因对SlGH3.4启动子活性进行的精细剖析。SlGH3.4启动子可在大豆和水稻植株的菌根根中以及生长素处理的大豆根中强烈驱动GUS表达，但在生长素处理的水稻根中则不能。启动子缺失分析揭示了三个顺式作用基序，即生长素响应元件AuxRE，以及两个新鉴定的基序MYCRS1和MYCRS2，它们参与生长素和AM介导的SlGH3.4表达的激活。从SlGH3.4启动子中删除AuxRE会导致对外源生长素诱导的GUS染色几乎完全消失。七个重复的AuxRE与花椰菜花叶病毒（CaMV）35S最小启动子融合后，可在生长素处理的和AM真菌定殖的烟草根中指导GUS表达。四个重复的MYCRS1或MYCRS2与CaMV35S最小启动子融合足以在含丛枝的细胞中驱动GUS表达，但在生长素处理的烟草根中则不能。总之，我们的结果为生长素和AM调控途径在调节不同菌根植物中AM响应的GH3基因表达时潜在的相互作用的分子机制提供了新的见解。
