Journal Article

Non-pathogenic Rhizobium radiobacter F4 deploys plant beneficial activity independent of its host Piriformospora indica

Alabid, Ibrahim, Kumar, Neelendra, Blom, Jochen, Rothballer, Michael, Guo, Huijuan, Kogel, Karl-Heinz, Hardt, Martin, Hartmann, Anton, Kämpfer, Peter, Imani, Jafargholi, Glaeser, Stefanie P, Goesmann, Alexander

2016

Overview

The Alphaproteobacterium Rhizobium radiobacter F4 ( Rr F4) was originally characterized as an endofungal bacterium in the beneficial endophytic Sebacinalean fungus Piriformospora indica . Although attempts to cure P. indica from Rr F4 repeatedly failed, the bacterium can easily be grown in pure culture. Here, we report on Rr F4’s genome and the beneficial impact the free-living bacterium has on plants. In contrast to other endofungal bacteria, the genome size of Rr F4 is not reduced. Instead, it shows a high degree of similarity to the plant pathogenic R. radiobacter (formerly: Agrobacterium tumefaciens ) C58, except vibrant differences in both the tumor-inducing (pTi) and the accessor (pAt) plasmids, which can explain the loss of Rr F4’s pathogenicity. Similar to its fungal host, Rr F4 colonizes plant roots without host preference and forms aggregates of attached cells and dense biofilms at the root surface of maturation zones. Rr F4-colonized plants show increased biomass and enhanced resistance against bacterial leaf pathogens. Mutational analysis showed that, similar to P. indica , resistance mediated by Rr F4 was dependent on the plant’s jasmonate-based induced systemic resistance (ISR) pathway. Consistent with this, Rr F4- and P. indica -induced pattern of defense gene expression were similar. In clear contrast to P. indica , but similar to plant growth-promoting rhizobacteria, Rr F4 colonized not only the root outer cortex but also spread beyond the endodermis into the stele. On the basis of our findings, Rr F4 is an efficient plant growth-promoting bacterium.

• Publisher: Nature Publishing Group UK,Oxford University Press,Nature Publishing Group
• Subject: 14/19 / 14/63 / 38/22 / 38/77 / 45/23 / 45/43 / 45/90 / 631/326 / 631/449 / Agrobacterium tumefaciens / Agrobacterium tumefaciens - physiology / Arabidopsis - immunology / Arabidopsis - microbiology / Arabidopsis - physiology / Bacteria / Basidiomycota - physiology / Biofilms / Biomedical and Life Sciences / Cell culture / Cyclopentanes - metabolism / Ecology / Endophytes / Evolutionary Biology / Gene expression / Genomes / Host plants / Host preferences / Jasmonic acid / Life Sciences / Microbial Ecology / Microbial Genetics and Genomics / Microbiology / Original / original-article / Oxylipins - metabolism / Pathogenicity / Pathogens / Piriformospora indica / Plant growth / Plant Immunity / Plant Leaves - microbiology / Plant roots / Plant Roots - microbiology / Plasmids / Pure culture / Rhizobium / Rhizobium radiobacter / Symbiosis