Evaluation of Legume–Rhizobial Symbiotic Interactions Beyond Nitrogen Fixation That Help the Host Survival and Diversification in Hostile Environments

Abstract

Plants often experience unfavorable conditions during their life cycle that impact their growth and sometimes their survival. A temporary phase of such stress, which can result from heavy metals, drought, salinity, or extremes of temperature or pH, can cause mild to enormous damage to the plant depending on its duration and intensity. Besides environmental stress, plants are the target of many microbial pathogens, causing diseases of varying severity. In plants that harbor mutualistic bacteria, stress can affect the symbiotic interaction and its outcome. To achieve the full potential of a symbiotic relationship between the host and rhizobia, it is important that the host plant maintains good growth characteristics and stay healthy under challenging environmental conditions. The host plant cannot provide good accommodation for the symbiont if it is infested with diseases and prone to other predators. Because the bacterium relies on metabolites for survival and multiplication, it is in its best interests to keep the host plant as stress-free as possible and to keep the supply stable. Although plants have developed many mitigation strategies to cope with stress, the symbiotic bacterium has developed the capability to augment the plant’s defense mechanisms against environmental stress. They also provide the host with protection against certain diseases. The protective features of rhizobial–host interaction along with nitrogen fixation appear to have played a significant role in legume diversification. When considering a legume–rhizobial symbiosis, extra benefits to the host are sometimes overlooked in favor of the symbionts’ nitrogen fixation efficiency. This review examines all of those additional considerations of a symbiotic interaction that enable the host to withstand a wide range of stresses, enabling plant survival under hostile regimes. In addition, the review focuses on the rhizosphere microbiome, which has emerged as a strong pillar of evolutionary reserve to equip the symbiotic interaction in the interests of both the rhizobia and host. The evaluation would draw the researchers’ attention to the symbiotic relationship as being advantageous to the host plant as a whole and the role it plays in the plant’s adaptation to unfavorable environmental conditions.

Biochar Enhances the Resistance of Legumes and Soil Microbes to Extreme Short-Term Drought

“…Legume–rhizobial symbiotic interactions beyond nitrogen fixation may have important roles in legume tolerance to drought [ 99 ], which can be tested using soil metabolome analysis. Both soil complex lipids and primary metabolites would significantly change under drought conditions [ 100 ].…”

Omics approaches in understanding the benefits of plant-microbe interactions

“…Microbes produce enzymes and metabolites that degrade complex plant molecules and enhance nutrient availability (Anderson, 2023 ; Puranik et al, 2023 ). Nitrogen-fixing bacteria such as Rhizobium leguminosarum convert atmospheric nitrogen to ammonia, thereby enhancing plant growth and soil fertility (Goyal and Habtewold, 2023 ). Phosphate-solubilizing microbes produce organic acids to solubilize phosphate minerals and promote plant growth (da Silva et al, 2023 ).…”

Microbial Insights into Biofortified Common Bean Cultivation

“…The symbiotic interactions between microorganisms and common bean plants not only improve the soil but also contribute to the crop's resilience to environmental stresses, such as drought and diseases. A well-structured and nutrient-enriched soil enables plants to better withstand adverse conditions and develop more robustly [67].…”