The model legume Medicago truncatula A17 is poorly matched for N₂ fixation with the sequenced microsymbiont Sinorhizobium meliloti 1021

Abstract

Summary• Medicago truncatula (barrel medic) A17 is currently being sequenced as a model legume, complementing the sequenced root nodule bacterial strain Sinorhizobium meliloti 1021 (Sm1021). In this study, the effectiveness of the Sm1021-M. truncatula symbiosis at fixing N 2 was evaluated.• N 2 fixation effectiveness was examined with eight Medicago species and three accessions of M. truncatula with Sm1021 and two other Sinorhizobium strains. Plant shoot dry weights, plant nitrogen content and nodule distribution, morphology and number were analysed.• Compared with nitrogen-fed controls, Sm1021 was ineffective or partially effective on all hosts tested (excluding M. sativa), as measured by reduced dry weights and shoot N content. Against an effective strain, Sm1021 on M. truncatula accessions produced more nodules, which were small, pale, more widely distributed on the root system and with fewer infected cells.• The Sm1021-M. truncatula symbiosis is poorly matched for N 2 fixation and the strain could possess broader N 2 fixation deficiencies. A possible origin for this reduction in effectiveness is discussed. An alternative sequenced strain, effective at N 2 fixation on M. truncatula A17, is Sinorhizobium medicae WSM419.New Phytologist (2008) 179: 62-66

NODULE ROOT and COCHLEATA Maintain Nodule Development and Are Legume Orthologs of Arabidopsis BLADE-ON-PETIOLE Genes

“…Consistent with this, we measured plant dry weight, commonly used as a proxy for measuring effectiveness of symbiosis (Terpolilli et al, 2008), and we showed that growth of mutant plants under symbiotic conditions is not adversely affected compared with wild-type plants (see Supplemental Table 1 online). In addition, histological observation of noot nodules (see Supplemental Figure 2 and Supplemental Table 2 online) showed that they have the characteristic zonation of wild-type nodules, are properly invaded by symbiotic bacteria, and contain differentiated symbiotic cells.…”

Novel Burkholderia bacteria isolated from Lebeckia ambigua – A perennial suffrutescent legume of the fynbos

“…The capacity for N 2 -fixation (effectiveness) was determined by comparing yields of inoculated plants with +N controls (5 ml of 10 mM KNO 3 applied weekly). The strains were separated into three groups as described by Terpolilli et al (2008); those considered effective (E) = >75% of +N control, partially effective (PE) = >20% but <75% of +N control, ineffective (I) = <20% of +N control or no nodulation (Nod-). General analyses of variance using a 5% least significant difference (LSD) were calculated on the data sets using GenStat 12 ® (Release 12.1, Lawes Agricultural Trust, Rothamsted Experimental Station) and are shown in the figure legends where appropriate.…”

Enhanced nodulation and symbiotic effectiveness of Medicago truncatula when co-inoculated with Pseudomonas fluorescens WSM3457 and Ensifer (Sinorhizobium) medicae WSM419

“…Plates were left at room temperature for 24-36 h, before germinated seedlings were transferred into a steam-sterilised mix of river sand and yellow sand (1:1). Plants were grown using the culture system described by (Howieson et al 1995), where deficiency of N limits legume growth except where they are effectively nodulated or are supplied with nitrogen (Terpolilli et al 2008).…”

“…This study was undertaken to investigate the effect of co-inoculation with WSM3457 on the kinetics of nodule initiation and development in M. truncatula when the symbiosis is challenged by a low inoculum dose of rhizobia. In glasshouse experiments legumes are often inoculated with 10 7 -10 9 root nodule bacteria (Hirsch et al 2009;Howieson et al 1995;Tang et al 2001;Terpolilli et al 2008). However, when seeds are inoculated prior to sowing in the field, the inoculum density is much lower, in the order of 10 4 cells per gram of seed.…”