Rhizobial diversity in New Zealand legumes
Bevan S. Weir1,2, Susan J. Turner2, Warwick B. Silvester3, Duck-Chul Park1, and John M. Young1 1. Landcare Research, Private Bag 92170, Auckland, New Zealand 2. School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand 3. Department of Biological Sciences, University of Waikato, Private Bag 3105, Hamilton, New Zealand
Contact: [email protected] Bevan Weir Web: http://www.rhizobia.co.nz
Abstract Utilising inferred phylogenies from gene sequence data it is shown that In New Zealand different genera of rhizobial populations nodulate native legumes, and exotic invasive weeds. The diversity of strains discovered contrasts with previous studies implying host legume specificity. The host range of Rhizobium leguminosarum is extended by the observation that it nodulates native New Zealand woody legumes.
Acacia longifolia Ulex europaeus (Gorse) Cytisus scoparius (Broom) Montigena novae-zelandiae Clianthus puniceus Carmichaelia australis Root nodule from Acacia longifolia
Methods Introduction • 36 bacterial isolates were obtained from the New Zealand has four genera of native legumes: root nodules of 9 native and 5 introduced weed Sophora, Carmichaelia, Clianthus and Montigena. legume species from throughout the country. Several exotic legumes (gorse, broom, Acacia) • 5 type strains of rhizobia were selected to have reached “super weed” status covering complement GenBank gene sequence data millions of hectares, and costing tens of millions of • Four genes (16S rDNA, atpD, glnII, recA) PCR dollars per year to control. Their success is due to, Isolated from native New Zealand legumes amplified and sequenced for 36 NZ strains and 5 R. leguminosarum isolated from NZ legumes 11736 (Sophora ) in part, their rhizobial symbioses. Isolated from exotic weed legumes 12649 (Carmichaelia) type strains 14330 (Sophora ) 15054 (Carmichaelia) • Phylogenetic trees were built for each gene New Zealand, as an island, has been separated 11719 (Sophora ) using Neighbour-Joining and Maximum 12637 (Sophora ) from the regions of major legume evolution for Mesorhizobium ciceri Likelihood methods, to assess the diversity and about 80 million years, yet exotic legumes were Mesorhizobium loti phylogenetic grouping of each strain, compared 12685 (Montigena ) introduced less than 200 years ago by early Mesorhizobium mediterraneum to type strains for selected rhizobial species. European settlers. Mesorhizobium tianshanense Mesorhizobium chacoense Mesorhizobium amorphae 11726 (Clianthus ) 11721 (Clianthus ) Mesorhizobium plurifarium Mesorhizobium huakuii 12635 (Carmichaelia) 11722 (Carmichaelia) 13190 (Carmichaelia) Results 11541 (Clianthus ) 11708 (Carmichaelia) 12690 (Montigena ) The phylogenetic trees produced were mostly 14319 (Carmichaelia) Sinorhizobium fredii congruent (only 16S rDNA shown here). Sinorhizobium sahelense Objectives Sinorhizobium meliloti Rhizobium etli It is clear that native legumes and exotic legumes 11727 (Carmichaelia) are nodulated by totally different rhizobial 11542 (Clianthus ) The purpose of this study was to identify the rhizobia 12687 (Carmichaelia) populations: Native legumes are nodulated by nodulating both native legumes and introduced 14642 (Sophora ) diverse Mesorhizobium populations and by Rhizobium leguminosarum weeds. Presumably the rhizobia associated with the Rhizobium tropici Rhizobium leguminosarum, whilst introduced native legumes have co-evolved over millions of Bradyrhizobium japonicum legumes are nodulated by diverse Bradyrhizobium yuanmingense years. But what species of rhizobia are the recently Bradyrhizobium liaoningense Bradyrhizobium spp. introduced legumes nodulating with? 14753 (Albizia ) 14755 (Acacia ) 12835 (Acacia ) No geographical distribution correlation was There are three possibilities: 14754 (Acacia ) evident (data not shown). 14533 (Ulex ) 14304 (Ulex ) 14320 (Ulex ) 1.They have adapted to use native rhizobial 12674 (Ulex ) The question of origin is now partially solved, the 14310 (Cytisus ) exotic legumes in this study must be using populations 14309 (Cytisus ) 14328 (Cytisus ) introduced or cosmopolitan rhizobial populations. 14292 (Ulex ) 2.Effective rhizobia were co-introduced along with 14291 (Cytisus ) the exotic legumes 5 changes 14306 (Ulex ) Additionally four native legumes were found to 14752 (Albizia ) 12624 (Cytisus ) nodulate with isolates of Rhizobium 3.Effective rhizobial cosmopolitan populations are Bradyrhizobium elkanii leguminosarum – this represents an extension to present in New Zealand soils. the host range of this species. These woody New Zealand legumes are very different to the currently accepted host range of the three The approach used in this study was to sequence biovars of R. leguminosarum. four housekeeping genes, and examining their Maximum Likelihood phylogenetic tree showing the inferred phylogeny. Multiple genes were used to relationship of rhizobia isolated from legumes present The widespread distribution of strains from establish species level placement and to identify in New Zealand, compared to type strains. Host individual native legume genera across gene transfer events that may confuse phylogenetic legume genus is indicated in the parentheses. Mesorhizobium contrast with previous reports inference. that imply the specificity of bacterial species to limited numbers of legume genera.
Acknowledgements – This study funded by a grant from the Marsden Fund, administered by the Royal Society of New Zealand