Unknown,Transcriptomics,Genomics,Proteomics

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Rhizobial adaptation to hosts, a new facet in the legume root-nodule symbiosis

ABSTRACT: Certain alpha- and beta-proteobacteria, the rhizobia, are able to infect legume roots, elicit root nodules, and live therein as endosymbiotic, nitrogen-fixing bacteroids. Host recognition and specificity are the results of consecutive programming events in bacteria and host plants in which important signaling molecules, e.g. plant flavonoids and rhizobial lipooligosaccharides, play key roles. Here, we introduce a new aspect of this symbiosis: the adaptive response to hosts. In contrast to host specificity, which determines early steps in bacteria-plant interaction, the adaptation to hosts refers to late events in mature bacteroids where specific genes are transcribed and translated that help the endosymbionts to meet the disparate environmental requirements imposed by the hosts in which they live. This concept was elaborated with Bradyrhizobium japonicum and three different legumes (soybean, cowpea, siratro). We systematically analyzed and compared the transcriptomes as well as the proteomes in bacteroids from root nodules of the three hosts. Transcripts and proteins were thus identified which are induced in only one of the three hosts. We then focused on those determinants that were congruent in the two data sets of host-specific transcripts and proteins, and arrived at 20 for soybean, 7 for siratro, and 4 for cowpea. One conspicuous gene cluster for a predicted ABC-type transporter, differentially expressed in siratro, was deleted. The corresponding mutant had a symbiotic defect on siratro rather than on soybean or cowpea. This result demonstrates the value of the applied approach and corroborates the host-specific adaptation concept. B. japonicum transcriptome was determined for the three different host plants

ORGANISM(S): Macroptilium atropurpureum

SUBMITTER: Hubert Rehrauer

PROVIDER: E-GEOD-18884 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Background. Cowpea, Vigna unguiculata L. Walp., is one of the most important food and forage legumes in the semi-arid tropics. While most cowpea accessions are susceptible to the root parasitic weed Striga gesnerioides, several cultivars have been identified that show race-specific resistance. Cowpea cultivar B301 contains the RSG3-301 gene for resistance to S. gesnerioides race SG3, but is susceptible to race SG4z. When challenged by SG3, roots of cultivar B301 develop a strong resistance response characterized by a hypersensitive reaction and cell death at the site of parasite attachment. In contrast, no visible response occurs in B301 roots parasitized by SG4z. Results. Gene expression in the roots of the cowpea cultivar B301 during compatible (susceptible) and incompatible (resistant) interactions with S. gesnerioides races SG4z and SG3, respectively, were investigated at 6 and 13 days post-inoculation (dpi), in the early and late stages of the resistance response using a Nimblegen custom design cowpea microarray. A total of 111 genes were differentially expressed in B301 roots at 6 dpi; this number increased to 2102 genes at 13 dpi. At 13 dpi, a total of 1944 genes were differentially expressed during compatible (susceptible) interactions of B301 with SG4z . Genes and pathways involved in signal transduction, programmed cell death and apoptosis, and defense response to biotic and abiotic stress were differentially expressed in the early resistance response; at the later time point, enrichment was primarily for defense-related gene expression, and genes encoding components of lignifications and secondary wall formation. In compatible interactions (B301 M-bM-^@M-^S SG4z), multiple defense pathways were repressed, including those involved in lignin biosynthesis and secondary cell wall modifications, while cellular transport processes for nitrogen and sulfur were increased. Conclusion. Distinct changes in global gene expression profiles occur in host roots following successful and unsuccessful attempted parasitism by Striga. Induction of specific defense related genes and pathways defines components of a unique resistance mechanism. Some genes and pathways up-regulated in the host resistance response to SG3 are repressed in the susceptible interactions, suggesting that the parasite is targeting specific components of the hostM-bM-^@M-^Ys defense. These results add to our understanding of plant-parasite interactions and the evolution of resistance to parasitic weeds. A Nimblegen custom design cowpea microarray investigating gene expression in the roots of the cowpea cultivar B301 during compatible (susceptible) and incompatible (resistant) interactions with S. gesnerioides races SG4z and SG3, respectively, at 6 and 13 days post-inoculation (dpi), in the early and late stages of the resistance response.

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Rhizobial adaptation to hosts, a new facet in the legume root-nodule symbiosis

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