Rhizobia: A Promising Source of Plant Growth-Promoting Molecules and Their Non-Legume Interactions: Examining Applications and Mechanisms

Abstract

For over a century, the scientific community has had a comprehensive understanding of how rhizobia can promote the growth of legumes by forming nitrogen fixing nodules. Despite this knowledge, the interaction of rhizobia with non-legumes has remained largely ignored as a subject of study until more recent decades. In the last few years, research has shown that rhizobia can also associate with non-legume roots, which ultimately leads to the stimulation of growth through diverse direct and indirect mechanisms. For example, rhizobia can enhance growth through phytohormones production, the improvement of plant nutrient uptake, such as the solubilization of precipitated phosphorus, the production of siderophores to address iron needs, and also the reduction of ethylene levels through the ACC deaminase enzyme to cope with drought stress. Additionally, rhizobia can improve, indirectly, non-legume growth through biocontrol of pathogens and the induction of systemic resistance in the host plant. It can also increase root adherence to soil by releasing exopolysaccharides, which regulate water and soil nutrient movement. The objective of this review is to assess and analyze the existing knowledge and information regarding the mechanisms through which rhizobia promote the growth of non-legumes. By conducting a comprehensive analysis of these findings, we aim to gain new insights into the development of Rhizobium/non-legume interactions.

Plant-microbe interactions: mechanisms and applications for improving crop yield and quality

“…Additionally, non-mycorrhizal fungi like Aspergillus, Alternaria, Fusarium, and Penicillium (Kalayu, 2019), as well as mycorrhizal fungi like Rhizophagus and Glomus (Zhang et al, 2018), and cyanobacteria genera like Anabaena and Westiellopsis (Yandigeri et al, 2011), and the yeast Rhodosporidium (Chen et al, 2023), are active phosphate-solubilizing representatives. The microorganisms recognized as highly efficient phosphate solubilizers include rhizobia species like R. leguminosarum, R. meliloti, M. mediterraneum, Bradyrhizobium sp., and B. japonicum (Fahde et al, 2023).…”

“…Siderophores are involved in bacterial signaling systems and may possess antibacterial properties, making siderophore-producing bacteria, especially rhizobia an instrument for the phytopathogen control (Johnstone & Nolan, 2015;Fahde et al, 2023).…”

“…The best known root nodule bacteria belong to the families Rhizobiaceae (-Proteobacteria) and Burkholderiaceae (-Proteobacteria), which are collectively referred to as rhizobia (Lindström & Mousavi, 2020;Fahde et al, 2023). These bacteria form a symbiotic relationship with important legumes, including alfalfa, beans, clover, peas, lupins, peanuts, and soybeans (Graham & Vance, 2003).…”

Rhizosphere Microorganisms Supply Availability of Soil Nutrients and Induce Plant Defense

“…Inside the nodules, the bacteria are released and transformed into bacteroids, capable of fixing atmospheric nitrogen via the enzyme nitrogenase. The legume plant, in return, supplies the bacteria with carbohydrates and other organic compounds, which are essential for the energy needs of the bacteria [ 60 ]. The fixed nitrogen, now in the form of ammonia, is assimilated by the plant and utilized to synthesize proteins, nucleic acids, and other vital compounds.…”

Progress in Microbial Fertilizer Regulation of Crop Growth and Soil Remediation Research

“…Among them, Rhizobium represents the epitome of symbiotic nitrogen fixation and is one of the most comprehensive studies on the symbiotic relationship between root nodules and nitrogen-fixing bacteria [59]. Rhizobium perceives flavonoid compounds exuded from plant root systems to produce signals for reciprocal communication with the root microbiome [60]. For instance, secretions from peanut root can stimulate the rhizobium of peanuts.…”