Centre for Rhizobium Studies, Murdoch University, Murdoch WA 6150, Australia.
Ann Bot. 2013 Jul;112(1):1-15. doi: 10.1093/aob/mct095. Epub 2013 May 26.
The legume clade Lotononis sensu lato (s.l.; tribe Crotalarieae) comprises three genera: Listia, Leobordea and Lotononis sensu stricto (s.s.). Listia species are symbiotically specific and form lupinoid nodules with rhizobial species of Methylobacterium and Microvirga. This work investigated whether these symbiotic traits were confined to Listia by determining the ability of rhizobial strains isolated from species of Lotononis s.l. to nodulate Listia, Leobordea and Lotononis s.s. hosts and by examining the morphology and structure of the resulting nodules.
Rhizobia were characterized by sequencing their 16S rRNA and nodA genes. Nodulation and N2 fixation on eight taxonomically diverse Lotononis s.l. species were determined in glasshouse trials. Nodules of all hosts, and the process of infection and nodule initiation in Listia angolensis and Listia bainesii, were examined by light microscopy.
Rhizobia associated with Lotononis s.l. were phylogenetically diverse. Leobordea and Lotononis s.s. isolates were most closely related to Bradyrhizobium spp., Ensifer meliloti, Mesorhizobium tianshanense and Methylobacterium nodulans. Listia angolensis formed effective nodules only with species of Microvirga. Listia bainesii nodulated only with pigmented Methylobacterium. Five lineages of nodA were found. Listia angolensis and L. bainesii formed lupinoid nodules, whereas nodules of Leobordea and Lotononis s.s. species were indeterminate. All effective nodules contained uniformly infected central tissue. Listia angolensis and L. bainesii nodule initials occurred on the border of the hypocotyl and along the tap root, and nodule primordia developed in the outer cortical layer. Neither root hair curling nor infection threads were seen.
Two specificity groups occur within Lotononis s.l.: Listia species are symbiotically specific, while species of Leobordea and Lotononis s.s. are generally promiscuous and interact with rhizobia of diverse chromosomal and symbiotic lineages. The seasonally waterlogged habitat of Listia species may favour the development of symbiotic specificity.
豆科黎豆族（广义，族名 Crotalarieae）包含三个属：丽豆属（Listia）、莱氏木属（Leobordea）和狭义的黎豆属（Lotononis s.s.）。Listia 物种具有共生专一性，与甲基杆菌属（Methylobacterium）和小单胞菌属（Microvirga）的根瘤菌形成羽扇豆型根瘤。本研究旨在通过确定从广义黎豆族（Lotononis s.l.）物种中分离的根瘤菌菌株能否结瘤 Listia、Leobordea 和狭义的黎豆属（Lotononis s.s.）宿主，以及检查由此产生的根瘤的形态和结构，来确定这些共生特性是否仅限于丽豆属（Listia）。
通过测序 16S rRNA 和 nodA 基因对根瘤菌进行了特征描述。在温室试验中，对八个分类学上不同的广义黎豆族（Lotononis s.l.）物种的结瘤和固氮能力进行了测定。使用光学显微镜检查了所有宿主的根瘤，以及在安哥拉丽豆（Listia angolensis）和丽豆（Listia bainesii）中感染和根瘤起始的过程。
与广义黎豆族（Lotononis s.l.）相关的根瘤菌在系统发育上具有多样性。莱氏木属（Leobordea）和狭义的黎豆属（Lotononis s.s.）的分离株与慢生根瘤菌属（Bradyrhizobium spp.）、苜蓿中华根瘤菌（Ensifer meliloti）、天山根瘤菌（Mesorhizobium tianshanense）和甲基杆菌属（Methylobacterium nodulans）最为密切相关。安哥拉丽豆（Listia angolensis）仅与小单胞菌属的物种形成有效根瘤。发现了 5 种 nodA 谱系。安哥拉丽豆（Listia angolensis）和丽豆（Listia bainesii）形成羽扇豆型根瘤，而莱氏木属（Leobordea）和狭义的黎豆属（Lotononis s.s.）物种形成不定形根瘤。所有有效的根瘤都含有均匀感染的中央组织。安哥拉丽豆（Listia angolensis）和丽豆（Listia bainesii）的根瘤起始于下胚轴的边缘和主根上，并在外部皮层层中发育根瘤原基。既没有看到根毛卷曲，也没有观察到感染线。
广义黎豆族（Lotononis s.l.）中存在两个专化性群：丽豆属（Listia）物种具有共生专一性，而莱氏木属（Leobordea）和狭义的黎豆属（Lotononis s.s.）物种通常是混杂的，与具有不同染色体和共生谱系的根瘤菌相互作用。安哥拉丽豆（Listia angolensis）物种季节性水淹的栖息地可能有利于共生专化性的发展。
