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Legumes of the Thar desert and their nitrogen fixing Ensifer symbionts

Ardley, Julie
Plant and soil 2017 v.410 no.1-2 pp. 517-520
Acacia, Ensifer, Vachellia, alkaline soils, dry environmental conditions, evolution, flora, fuels, genes, horizontal gene transfer, legumes, loci, microsymbionts, nitrogen fixation, people, ribosomal RNA, sequence analysis, shrubs, symbiosis, India, Thar Desert
BACKGROUND: Nodulated legumes form a large component of the flora of desert regions, but comparatively few studies have characterised their symbiotic interactions, or their rhizobial microsymbionts. The Thar desert is a sub-tropical desert with infertile, alkaline soils in the northwestern part of the Indian subcontinent, which is home to a large number of legumes that provide food and fuel, or are of medicinal importance to the local people. In the latest in a series of studies on the nodulated legumes of the Thar desert and their associated rhizobia, Sankhla et al. (2016), this issue, have characterised strains of Ensifer rhizobia isolated from nodules of the native mimosoid legume shrub Vachellia (Acacia) jacquemontii. SCOPE: These studies suggest that Ensifer rhizobia are the dominant microsymbionts of legumes native to the Thar desert and are particularly well-adapted to the arid conditions and alkaline soils found there. The Ensifer strains that nodulate V. jacquemontii may constitute a novel species, based on 16S rRNA and Multi Locus Sequence Analysis. Symbiotic adaptation of these rhizobia to local host legumes has involved horizontal gene transfer of symbiosis genes. CONCLUSIONS: These findings provide further insights into the evolution of legume-rhizobia symbioses and how plants and rhizobia are adapted to and can survive in stressful conditions.