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

Abstract

The Alphaproteobacterium Rhizobium radiobacter F4 (RrF4) was originally characterized as an endofungal bacterium in the beneficial endophytic Sebacinalean fungus Piriformospora indica. Although attempts to cure P. indica from RrF4 repeatedly failed, the bacterium can easily be grown in pure culture. Here, we report on RrF4's genome and the beneficial impact the free-living bacterium has on plants. In contrast to other endofungal bacteria, the genome size of RrF4 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 RrF4's pathogenicity. Similar to its fungal host, RrF4 colonizes plant roots without host preference and forms aggregates of attached cells and dense biofilms at the root surface of maturation zones. RrF4-colonized plants show increased biomass and enhanced resistance against bacterial leaf pathogens. Mutational analysis showed that, similar to P. indica, resistance mediated by RrF4 was dependent on the plant's jasmonate-based induced systemic resistance (ISR) pathway. Consistent with this, RrF4-and P. indica-induced pattern of defense gene expression were similar. In clear contrast to P. indica, but similar to plant growth-promoting rhizobacteria, RrF4 colonized not only the root outer cortex but also spread beyond the endodermis into the stele. On the basis of our findings, RrF4 is an efficient plant growth-promoting bacterium.

A Poly(A) Ribonuclease Controls the Cellotriose-Based Interaction between Piriformospora indica and Its Host Arabidopsis

“…However, a knockout line for this protein was not 211 Sharma et al (2008), Glaeser et al (2016) and demonstrated that P. indica 212 forms an intimate association with Rhizobium radiobacter F4, an alpha-Proteobacterium. The 213 endophytic bacterium shows a high degree of similarity to the plant pathogenic R. radiobacter…”

Effects of strategic tillage and plant hormone treatments on wheat-associated microbial communities

“…Bacteria lacking the capability to colonize and infection can enter plant endophytic niches via wounds and cracks on the plant, which is documented as the passive mode of endophytic colonization (Christina et al, 2013) (Fig.1). work conducted by Compant et al (2005; and Glaeser et al (2016).…”

“…Current evidence also reveals that some bacteria live in symbiosis with plant endophytic fungi (Desirò et al, 2015;Glaeser et al, 2016). Interestingly, some endofungal bacteria colonize plants in a similar fashion as their fungal host.…”

“…Endophytic bacteria engaging in different life styles are depicted by colored ovals (not to scale). This illustration was inspired by work conducted by Compant et al (2005; and Glaeser et al (2016) Fig. 3 Schematic representation summarizing the typical properties of endophytic bacteria to cope with plant defenses.…”

“…Interestingly, some endofungal bacteria colonize plants in a similar fashion as their fungal host. For instance, the endofungal bacterium Rhizobium radiobacter F4 hosted by the fungus Piriformospora indica colonizes plant roots and forms aggregates of attached cells and dense biofilms at the root surface (Glaeser et al, 2016).…”