Ampe Frederic, Kiss Ernö, Sabourdy Frédérique, Batut Jacques
Laboratoire de Biologie Moléculaire des Relations Plantes-Microorganismes, UMR 215 Centre National de la Recherche Scientifique - Institut National de la Recherche Agronomique, BP27-31326 Castanet-Tolosan cedex, France.
Genome Biol. 2003;4(2):R15. doi: 10.1186/gb-2003-4-2-r15. Epub 2003 Jan 31.
Rhizobia induce the formation on specific legumes of new organs, the root nodules, as a result of an elaborated developmental program involving the two partners. In order to contribute to a more global view of the genetics underlying this plant-microbe symbiosis, we have mined the recently determined Sinorhizobium meliloti genome sequence for genes potentially relevant to symbiosis. We describe here the construction and use of dedicated nylon macroarrays to study simultaneously the expression of 200 of these genes in a variety of environmental conditions, pertinent to symbiosis.
The expression of 214 S. meliloti genes was monitored under ten environmental conditions, including free-living aerobic and microaerobic conditions, addition of the plant symbiotic elicitor luteolin, and a variety of symbiotic conditions. Five new genes induced by luteolin have been identified as well as nine new genes induced in mature nitrogen-fixing bacteroids. A bacterial and a plant symbiotic mutant affected in nodule development have been found of particular interest to decipher gene expression at the intermediate stage of the symbiotic interaction. S. meliloti gene expression in the cultivated legume Medicago sativa (alfalfa) and the model plant M. truncatula were compared and a small number of differences was found.
In addition to exploring conditions for a genome-wide transcriptome analysis of the model rhizobium S. meliloti, the present work has highlighted the differential expression of several classes of genes during symbiosis. These genes are related to invasion, oxidative stress protection, iron mobilization, and signaling, thus emphasizing possible common mechanisms between symbiosis and pathogenesis.
根瘤菌通过一个涉及这两个共生伙伴的精细发育程序，诱导特定豆科植物形成新器官——根瘤。为了更全面地了解这种植物 - 微生物共生关系的遗传学基础，我们在最近测定的苜蓿中华根瘤菌基因组序列中挖掘了可能与共生相关的基因。我们在此描述了专用尼龙宏阵列的构建和使用，以同时研究这些基因中的200个在与共生相关的各种环境条件下的表达情况。
在十种环境条件下监测了214个苜蓿中华根瘤菌基因的表达，这些条件包括自由生活的需氧和微需氧条件、添加植物共生诱导剂木犀草素以及各种共生条件。已鉴定出五个由木犀草素诱导的新基因以及九个在成熟固氮类菌体中诱导表达的新基因。发现了两个在根瘤发育中受影响的细菌和植物共生突变体，它们对于解读共生相互作用中间阶段的基因表达特别有意义。比较了苜蓿中华根瘤菌在栽培豆科植物紫花苜蓿和模式植物蒺藜苜蓿中的基因表达，发现了少量差异。
除了探索对模式根瘤菌苜蓿中华根瘤菌进行全基因组转录组分析的条件外，本研究还突出了共生过程中几类基因的差异表达。这些基因与侵染、氧化应激保护、铁离子动员和信号传导有关，从而强调了共生和致病过程之间可能存在的共同机制。
