Boisson-Dernier Aurélien, Andriankaja Andry, Chabaud Mireille, Niebel Andreas, Journet Etienne P, Barker David G, de Carvalho-Niebel Fernanda
Laboratory of Plant Microbe Interactions, CNRS-INRA, BP 52627, 31326 Castanet-Tolosan, France.
Mol Plant Microbe Interact. 2005 Dec;18(12):1269-76. doi: 10.1094/MPMI-18-1269.
The MtENOD11 gene from the model legume Medicago truncatula is transcriptionally activated both in response to Sinorhizobium meliloti Nod factors and throughout infection of root tissues by the nitrogen-fixing microsymbiont. To identify the regulatory sequences involved in symbiosis-related MtENOD11 expression, a series of promoter deletions driving the beta-glucuronidase reporter gene were analyzed in transgenic M. truncatula roots. These studies have revealed that distinct regulatory regions are involved in infection-related MtENOD11 expression compared with preinfection (Nod factor-mediated) expression. In particular, the 257-bp promoter sequence immediately upstream from the start codon is sufficient for infection-related expression, but is unable to drive gene transcription in response to the Nod factor elicitor. This truncated promoter is also sufficient to confer MtENOD11 expression during both the arbuscular mycorrhizal (AM) association and the parasitic interaction with root-knot nematodes. Site-directed mutagenesis further showed that a previously identified nodule-specific AT-rich motif is required for high-level MtENOD11 expression during S. meliloti infection as well as during AM colonization. However, mutation of this motif does not affect gene expression associated with nematode-feeding sites. Taken together, these results suggest a close link between regulatory mechanisms controlling transcriptional early nodulin gene activation during both rhizobial and AM root endosymbioses.
来自模式豆科植物蒺藜苜蓿的MtENOD11基因在响应苜蓿中华根瘤菌的结瘤因子时以及在固氮微共生体对根组织的整个感染过程中都会被转录激活。为了鉴定参与共生相关的MtENOD11表达的调控序列，在转基因蒺藜苜蓿根中分析了一系列驱动β-葡萄糖醛酸酶报告基因的启动子缺失。这些研究表明，与感染前（结瘤因子介导的）表达相比，不同的调控区域参与了与感染相关的MtENOD11表达。特别是，起始密码子上游紧邻的257 bp启动子序列足以实现与感染相关的表达，但不能驱动基因响应结瘤因子诱导物进行转录。这个截短的启动子在丛枝菌根（AM）共生以及与根结线虫的寄生相互作用过程中也足以赋予MtENOD11表达。定点诱变进一步表明，先前鉴定的一个结节特异性富含AT的基序对于苜蓿中华根瘤菌感染期间以及AM定殖期间的高水平MtENOD11表达是必需的。然而，这个基序的突变并不影响与线虫取食位点相关的基因表达。综上所述，这些结果表明在根瘤菌和AM根内共生过程中控制转录早期结瘤素基因激活的调控机制之间存在密切联系。
