放线菌中的Frankia通常与桤木形成共生固氮的根瘤，不能与豆科植物形成根瘤。Trujillo等人的新近研究表明，放线菌中的另外一类菌小单胞菌属的细菌却能与豆科植物（如狭叶羽扇豆）形成根瘤，并且根瘤有固氮活性，扩增到的nifH基因与Frankia的相似性高达99%。原位杂交也表明，这些小单胞菌属的放线菌确实存在于根瘤内。其形成根瘤的机制还不清楚。另外由于Frankia没有根瘤菌所拥有的结瘤基因(nod)，小单胞菌属是否拥有结瘤基因，也还未知。 相关论文如下： ISME J. 2010 May 6. The genus Micromonospora is widespread in legume root nodules: the example of Lupinus angustifolius. Trujillo ME , Alonso-Vega P , Rodrguez R , Carro L , Cerda E , Alonso P , Martnez-Molina E . Departamento de Microbiologa y Gentica, Edificio Departamental Lab. 205, Campus Miguel de Unamuno, Universidad de Salamanca, Salamanca, Spain. Abstract Our current knowledge of plant-microbe interactions indicate that populations inhabiting a host plant are not restricted to a single microbial species but comprise several genera and species. No one knows if communities inside plants interact, and it has been speculated that beneficial effects are the result of their combined activities. During an ecological study of nitrogen-fixing bacterial communities from Lupinus angustifolius collected in Spain, significant numbers of orange-pigmented actinomycete colonies were isolated from surface-sterilized root nodules. The isolates were analysed by BOX-PCR fingerprinting revealing an unexpectedly high genetic variation. Selected strains were chosen for 16S rRNA gene sequencing and phylogenetic analyses confirmed that all strains isolated belonged to the genus Micromonospora and that some of them may represent new species. To determine the possibility that the isolates fixed atmospheric nitrogen, chosen strains were grown in nitrogen-free media, obtaining in some cases, significant growth when compared with the controls. These strains were further screened for the presence of the nifH gene encoding dinitrogenase reductase, a key enzyme in nitrogen fixation. The partial nifH-like gene sequences obtained showed a 99% similarity with the sequence of the nifH gene from Frankia alni ACN14a, an actinobacterium that induces nodulation and fixes nitrogen in symbiosis with Alnus. In addition, in situ hybridization was performed to determine if these microorganisms inhabit the inside of the nodules. This study strongly suggests that Micromonospora populations are natural inhabitants of nitrogen-fixing root nodules.The ISME Journal advance online publication, 6 May 2010; doi:10.1038/ismej.2010.55. PMID: 20445637
1. Rhizobase: http://genome.kazusa.or.jp/rhizobase/ 2. Legume Information Systems (Resources for the legume research community): http://comparative-legumes.org/index.php/Home 3. Legume database: http://www.legumebase.brc.miyazaki-u.ac.jp/index.jsp 目前只有两种植物的数据：百脉根和大豆.
下面的问题由Catherine Masson-Boivin等人提出，发表在 Trends in Microbiology 上，详见： doi:10.1016/j.tim.2009.07.004 。值得我们去深思。 1. 根瘤菌具有很大的多样性，能否超出目前的，-变形杆菌门？结瘤基因如何起源的？（ Does rhizobium diversity extend beyond a- and b-proteobacteria? What is the origin of nod genes? ） 2. 不依赖于结瘤因子（NF）的结瘤机制是什么？它与由结瘤因子引起的结瘤这种机制的关系是什么？是否不与NF有关的结瘤机制只局限于合萌属这类植物？自然界中有无其它的结瘤机制呢？ （ What is the actual mechanism for NF-independent nodulation? How is it related to the NF strategy? Is the NF-independent strategy restricted to Aeschynomene plants? Are there additional nodulation strategies in nature?） 3.根瘤菌的表面多糖在侵染豆科植物过程中的精确任务是什么？它们是不是一些信号的受体？哪一种侵染机制与不依赖于NF的入侵有关？根瘤菌是如何进入根瘤细胞并在其中稳定存在的？（ What is the precise role of surface polysaccharides in infection? Are there receptors for signaling? Which infection mechanisms are associated with NF-independent crack-entry? How are rhizobia internalized and maintained in nodule cells?） 4.如果一个受体基因组接收了nod和nif基因从而进化成根瘤菌，那么这个受体菌的遗传素因究竟是什么？受体和供体基因组之间的系统发育关系究竟是远是近？接收nod和nif的机制是什么呢？（ What genetic predisposition should a recipient genome of nod and nif genes display for evolving into a rhizobium? How phylogenetically distant can the recipient and donor genomes be? What are the adaptive mechanisms required?） 5. 共生体的进化是从原始的形式（如不依赖于NF，通过裂隙进入）到精密的方式（依赖NF，有侵染线的形成）？（ Has symbiosis evolved from primitive (e.g. NF-independent, crack-entry) to sophisticated (NF, infection thread) strategies?） 6. 在一定时期分化形成类菌体（在山羊豆族的根瘤内）是否是形成固氮器官的必经步骤？（ Do the terminally differentiated bacteroids (found in galegoid nodules) constitute a step towards a N 2 -fixing organelle?） 7. 在结瘤的哪一阶段，T3SS和T4SS分泌效应子？Nops转移到植物胞质是这一功能实施所必须？（ At what stages of the nodulation process do T3SS and T4SS secrete effectors? Is translocation of Nops into plant cytoplasm required for their function?） 8. T3SS-和T4SS-依赖的效应子的受体是什么，它们是否能增强或是抑制在特定宿主植物上的结瘤作用？（ What are the targets of T3SS- and T4SS-dependent effectors that either enhance or impair nodulation of certain hosts?）
标签: 豆科植物
