Impact of root exudates and plant defense signaling on bacterial communities in the rhizosphere. A review

Abstract

Despite significant advances in crop protection, plant diseases cause a 20% yield loss in food and cash crops worldwide. Therefore, interactions between plants and pathogens have been studied in great detail. In contrast, the interplay between plants and non-pathogenic microorganisms has received scant attention, and differential responses of plants to pathogenic and non-pathogenic microorganisms are as yet not well understood. Plants affect their rhizosphere microbial communities that can contain beneficial, neutral and pathogenic elements. Interactions between the different elements of these communities have been studied in relation to biological control of plant pathogens. One of the mechanisms of disease control is induced systemic resistance (ISR). Studies on biological control of plant diseases have focused on ISR the last decade, because ISR is effective against a wide range of pathogens and thus offers serious potential for practical applications in crop protection. Such applications may however affect microbial communities associated with plant roots and interfere with the functioning of the root microbiota. Here, we review the possible impact of plant defense signaling on bacterial communities in the rhizosphere. To better assess implications of shifts in the rhizosphere microflora we first review effects of root exudates on soil microbial communities. Current knowledge on inducible defense signaling in plants is discussed in the context of recognition and systemic responses to pathogenic and beneficial microorganisms. Finally, the as yet limited knowledge on effects of plant defense on rhizosphere microbial communities is reviewed and we discuss future directions of research that will contribute to unravel the molecular interplay of plants and their beneficial microflora.

Antibiotic resistance genes in manure-amended soil and vegetables at harvest

“…It was also found that planting had certain effect on the fate of ARGs in manure-amended soil. For example, sulI and tetC genes had significantly higher abundance in control soil than in lettuce and endive planted soil in 30 d. While tetG, tetA, tetC, and tetM genes had higher abundance in control soil than in lettuce and endive planted soil in 60 d. This phenomenon may be partially caused by root exudates such as sugars, organic acids, and amino acids, which may create a low selective pressure of the antibiotics [18,37]. Unexpectedly, no significant difference was found for the detected ARGs between bulk and rhisosphere soil (except tetX).…”

Properties of the halophyte microbiome and their implications for plant salt tolerance

“…The composition of actively and passively released primary and secondary metabolites varies with plant species, developmental stage and environmental conditions. It has been demonstrated that the plant influences the soil microbial communities and its colonising microbiota via the exudate composition (Bais et al 2006;Faure et al 2009;Doornbos et al 2012). The beneficial effects provoked by endophytes result from nitrogen fixation, phytohormone production, supply of nutrients and pathogen suppression (Rosenblueth and Martinez-Romero 2006;Hardoim et al 2008) and those mechanisms also account for the alleviating effects of microorganisms when host plants face unfavourable environmental conditions.…”

Next-Generation Bio-Products Sowing the Seeds of Success for Sustainable Agriculture

“…For example, microorganisms' response to root exudates and root morphology was shown to shape rhizosphere microbial communities [7][8][9][10]. In addition, plant defense signaling play a role in this process [11].…”