The structure of the culturable root bacterial endophyte community of Nicotiana attenuata is organized by soil composition and host plant ethylene production and perception

Abstract

Summary• A plant's bacterial endophyte community is thought to be recruited from the rhizosphere, but how this recruitment is influenced by the plant's phytohormone signaling is unknown. Ethylene regulates plant-microbe interactions; here, we assess the role of ethylene in the recruitment of culturable endophytic bacteria from native soils.• We grew wild-type Nicotiana attenuata plants and isogenic transformed plants deficient in ethylene biosynthesis (ir-aco1) or perception (35S-etr1) in four native soils and quantified the extent of culturable bacterial endophyte colonization (by plate counting) and diversity (by amplified rDNA restriction analysis and 16S rDNA sequencing).• The endophyte community composition was influenced by soil type and ethylene signaling. Plants grown in organic (vs mineral) soils harbored a more diverse community and plants impaired in ethylene homeostasis harbored a less diverse community than wild-type plants. Wild-type and ethylene signaling-impaired plants fostered distinct bacteria in addition to common ones. In vitro re-colonization by common and genotype-specific isolates demonstrated the specificity of some associations and the susceptibility of 35S-etr1 seedlings to all tested bacterial isolates, suggesting an active process of colonization driven by plant-and microbespecific genes.• We propose that soil composition and ethylene homeostasis play central roles in structuring the bacterial endophyte community in N. attenuata roots.

Dimethyl Disulfide Produced by the Naturally Associated Bacterium Bacillus sp B55 Promotes Nicotiana attenuata Growth by Enhancing Sulfur Nutrition

“…Germination procedures have been described elsewhere (Ryu et al, 2003;Long et al, 2010). The plant growth-promoting Bacillus sp B55 strain (GenBank accession number JX101913) was isolated from a 35S-etr1 plant grown in native Utah soil in 2008 (Long et al, 2010).…”

“…Recently, several studies have highlighted ET's prominent role in mediating mutualistic plant-microbe interactions (Penmetsa and Cook, 1997;Iniguez et al, 2005;Long et al, 2010) and due to its gaseous nature, studies on microbial VOC-mediated signaling processes in plants have focused on ET (Bailly and Weisskopf, 2012). Indeed, ethylene insensitive2 mutants are nonresponsive to VOC-mediated PGP by B. amyloliquefaciens IN937 and Piriformospora indica (Ryu et al, 2003;Camehl et al, 2010).…”

“…We have previously shown that ET signaling determines the culturable bacterial endophyte community in roots of Coyote tobacco (Nicotiana attenuata) in the natural environment and identified natural root-associated bacteria that improve N. attenuata growth and survival (Long et al, 2010). Bacillus sp B55, isolated from ET-insensitive transgenic N. attenuata plants (35S-etr1, which heterologously express the mutant Arabidopsis receptor ETR1-1), causes dramatically increased survival and growth of 35S-etr1 plants grown in nature (Meldau et al, 2012).…”

Development of LNA oligonucleotide–PCR clamping technique in investigating the community structures of plant-associated bacteria

“…Other than seed-borne bacteria, plants have also been known to recruit bacteria from the surrounding soil during germination. 33,34) Potato might have a different survival strategy from that of soybean in the early growth stage. Further study is needed to investigate this hypothesis.…”

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

“…ET signaling influenced the endophytic bacterial communities in Nicotiana attenuate. It was observed that isogenic transformed plants impaired in ET biosynthesis (ir-aco1) or perception (35S-etr1) plants harbored culturable bacterial communities of a lower diversity than wild-type plants (Long et al, 2010). From the abovementioned studies, it seems that contrary to the studies on single bacterial isolates, the influence of the signaling pathways on endophytic bacterial communities are variable and may be small.…”