Motility, Adhesion and c-di-GMP Influence the Endophytic Colonization of Rice by Azoarcus sp. CIB.

Helga Fernández-Llamosas,Eduardo Díaz,Manuel Carmona

doi:10.3390/microorganisms9030554

Helga Fernández-Llamosas, Eduardo Díaz + Show 1 more

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https://doi.org/10.3390/microorganisms9030554

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Abstract

Proficient crop production is needed to ensure the feeding of a growing global population. The association of bacteria with plants plays an important role in the health state of the plants contributing to the increase of agricultural production. Endophytic bacteria are ubiquitous in most plant species providing, in most cases, plant promotion properties. However, the knowledge on the genetic determinants involved in the colonization of plants by endophytic bacteria is still poorly understood. In this work we have used a genetic approach based on the construction of fliM, pilX and eps knockout mutants to show that the motility mediated by a functional flagellum and the pili type IV, and the adhesion modulated by exopolysaccarides are required for the efficient colonization of rice roots by the endophyte Azoarcus sp. CIB. Moreover, we have demonstrated that expression of an exogenous diguanylate cyclase or phophodiesterase, which causes either an increase or decrease of the intracellular levels of the second messenger cyclic di-GMP (c-di-GMP), respectively, leads to a reduction of the ability of Azoarcus sp. CIB to colonize rice plants. Here we present results demonstrating the unprecedented role of the universal second messenger cyclic-di-GMP in plant colonization by an endophytic bacterium, Azoarcus sp. CIB. These studies pave the way to further strategies to modulate the interaction of endophytes with their target plant hosts.

Highlights

Plant associated bacteria play a fundamental role in the healthy state of the plant by contributing to its nutrition, development and defense [1,2,3]
Since the second messenger c-di-GMP is connected with motility and adhesion, in this work we investigated if the levels of c-di-GMP control the ability of the bacterium to colonize plant, an aspect scarcely explored in endophytes
CIBdfliM strain was around an order of magnitude lower (3.4 × per g of roots) than those recovered from seedlings inoculated with the wild type CIB strain (4.5 × per g of roots) (Figure 1B). These results indicate an important role of the flagellum at some stage of the endophytic colonization of rice by Azoarcus sp

Summary

Introduction

Plant associated bacteria play a fundamental role in the healthy state of the plant by contributing to its nutrition, development and defense [1,2,3]. A good number of the plant-associated bacteria colonize the plant tissues as endophytes being the roots the major target for endophytic colonization [2]. The effective root colonization by endophytic bacteria involves the coordinated expression of a number of gene factors, many of which are still poorly understood [7,8,9,10]. To analyze the genes involved in plant colonization several genomes from endophytic bacteria were compared [2,11,12,13,14]

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