Genes related to redox and cell curvature facilitate interactions between Caulobacter strains and Arabidopsis.

Louis Berrios,Bert Ely,Ying Ma

doi:10.1371/journal.pone.0249227

Abstract

Bacteria play an integral role in shaping plant growth and development. However, the genetic factors that facilitate plant-bacteria interactions remain largely unknown. Here, we demonstrated the importance of two bacterial genetic factors that facilitate the interactions between plant-growth-promoting (PGP) bacteria in the genus Caulobacter and the host plant Arabidopsis. Using homologous recombination, we disrupted the cytochrome ubiquinol oxidase (cyo) operon in both C. vibrioides CB13 and C. segnis TK0059 by knocking out the expression of cyoB (critical subunit of the cyo operon) and showed that the mutant strains were unable to enhance the growth of Arabidopsis. In addition, disruption of the cyo operon, metabolomic reconstructions, and pH measurements suggested that both elevated cyoB expression and acid production by strain CB13 contribute to the previously observed inhibition of Arabidopsis seed germination. We also showed that the crescent shape of the PGP bacterial strain C. crescentus CB15 contributes to its ability to enhance plant growth. Thus, we have identified specific genetic factors that explain how select Caulobacter strains interact with Arabidopsis plants.

Highlights

Terrestrial plants and microbes have been coevolving for over 100 million years [1], and their interactions contribute to global biogeochemical cycles and agricultural fecundity [2]
Since our previous analyses suggested that the expression of betalain synthesis related genes may contribute to the Caulobacter-mediated plant growth enhancement that we observed in our system [22], we knocked-out the expression of the cyoB gene that is predicted to code for an enzyme that is involved in the biosynthesis of betalain
The one exception was that seeds that were inoculated with CB13ΔcyoB cells were unable to increase basal rosette diameter (BRD) relative to control conditions, but seeds that were inoculated with C. segnisΔcyoB cells were still able to enhance BRD relative to control conditions (Fig 1B)

Summary

Introduction

Terrestrial plants and microbes have been coevolving for over 100 million years [1], and their interactions contribute to global biogeochemical cycles and agricultural fecundity [2]. Recent advances in microbial ecology have facilitated taxonomical and functional classifications of plant-associated microbes (PAMs), and core plant microbiomes (conserved microbial taxa) have begun to be identified across various plant species and diverse geographic regions [3,4]. Sequence-based approaches have highlighted the abundance of Alphaproteobacteria species in (endosphere) and around (rhizosphere) the roots of many plant genera such as Arabidopsis, Glycine, Hordeum, Panicum, Sorghum, Triticum, and Zea mays across diverse geographical regions [5,6,7,8,9,10,11,12].

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Conclusion