PDF(Pubmed)
Abstract：
Rhizobium leguminosarum bv. viciae (Rlv) UPM791 effectively nodulates pea and lentil, but bacteroids contain a number of proteins differentially expressed depending on the host. One of these host-dependent proteins (C189) is similar to a diaminobutyrate-2-oxoglutarate aminotransferase (DABA-AT). DABA-AT activity was demonstrated with cell extracts and with purified protein, so C189 was renamed as Dat. The dat gene was strongly induced in the central, active area of pea nodules, but not in lentil. Mutants defective in dat were impaired in symbiotic performance with pea plants, exhibiting reduced shoot dry weight, smaller nodules, and a lower competitiveness for nodulation. In contrast, there were no significant differences between mutant and wild-type in symbiosis with lentil plants. A comparative metabolomic approach using cell-free extracts from bacteroids induced in pea and lentil showed significant differences among the strains in pea bacteroids whereas no significant differences were found in lentil. Targeted metabolomic analysis revealed that the dat mutation abolished the presence of 2,4-diaminobutyrate (DABA) in pea nodules, indicating that DABA-AT reaction is oriented toward the production of DABA from L-aspartate semialdehyde. This analysis also showed the presence of L-homoserine, a likely source of aspartate semialdehyde, in pea bacteroids but not in those induced in lentil. The dat mutant showed impaired growth when cells were grown with L-homoserine as nitrogen source. Inclusion of DABA or L-homoserine as N source suppressed pantothenate auxotropy in Rlv UPM791, suggesting DABA as source of the pantothenate precursor β-alanine. These data indicate that Rlv UPM791 Dat enzyme is part of an adaptation mechanism of this bacterium to a homoserine-rich environment such as pea nodule and rhizosphere.
摘要：
豆科根瘤菌。viciae（Rlv）UPM791有效地结瘤豌豆和小扁豆，但是类细菌含有许多差异表达的蛋白质，这取决于宿主。这些宿主依赖性蛋白质之一（C189）类似于二氨基丁酸-2-氧代戊二酸氨基转移酶（DABA-AT）。用细胞提取物和纯化的蛋白质证明了DABA-AT活性，所以C189更名为Dat。dat基因在中央被强烈诱导，豌豆结节的活跃区域，但不是扁豆。dat缺陷突变体与豌豆植物的共生性能受损，表现出降低的枝条干重，较小的结节，和较低的结瘤竞争力。相比之下,与小扁豆植物共生的突变体和野生型之间没有显着差异。使用豌豆和小扁豆中诱导的类细菌的无细胞提取物的比较代谢组学方法显示，豌豆类细菌的菌株之间存在显着差异，而小扁豆中没有发现显着差异。有针对性的代谢组学分析显示，dat突变消除了豌豆结节中2,4-二氨基丁酸（DABA）的存在，表明DABA-AT反应倾向于从L-天冬氨酸半醛生产DABA。该分析还显示了L-高丝氨酸的存在，可能是天冬氨酸半醛的来源,在豌豆类细菌中，但在小扁豆中诱导的细菌中没有。当细胞以L-高丝氨酸作为氮源生长时，dat突变体显示出生长受损。包含DABA或L-高丝氨酸作为N源抑制了RlvUPM791中的泛酸营养缺陷型，表明DABA是泛酸前体β-丙氨酸的来源。这些数据表明RlvUPM791Dat酶是该细菌对富含高丝氨酸的环境如豌豆结节和根际的适应机制的一部分。
