Rhizobial-host interactions and symbiotic nitrogen fixation in legume crops toward agriculture sustainability

Authors: GOYAL, RAVINDER - Lacombe Research Centre; Mattoo, Autar; SCHMIDT, AUGUSTA - Lacombe Research Centre

Submitted to: Frontiers in Microbiology
Publication Type: Review Article
Publication Acceptance Date: 4/29/2021
Publication Date: 6/11/2021
Citation: Goyal, R.K., Mattoo, A.K., Schmidt, A.M. 2021. Rhizobial-host interactions and symbiotic nitrogen fixation in legume crops toward agriculture sustainability. Frontiers in Microbiology. https://doi.org/10.3389/fmicb.2021.669404.
DOI: https://doi.org/10.3389/fmicb.2021.669404

Interpretive Summary: Significant progress has been made in the identification of quantitative trait loci (QTLs) that determine nitrogen fixation in a symbiotic process confined to select commercial grain legumes. The adoption of this information in breeding programs will depend on recognizing biological nitrogen fixation (BNF) as an important part of agriculture sustainability. BNF is a complex phenomenon governed by the presence of genetic elements in both the host and Rhizobium compared to other allelic traits in crops. Nitrogen supplementation being an essential macronutrient with dramatic effects on productivity, was not until recently viewed as a threat to the environment when its effects on greenhouse gas production and pollution of aquatic systems clearly became evident. Associated environmental issues have become compelling enough to consider environmentally friendly options. The effectiveness of identified QTLs can contribute to their incorporation into breeding efforts. More studies on QTLs with expansion to other legume crops would strengthen them as candidates of the BNF trait. The existing knowledge along with robust soil microbiome profiles can be used to optimize the host-rhizobia interactions, particularly when new legume crops are introduced in the soil and environment. This review is of interest to crop scientists, breeders, microbiologists, and agronomists.

Technical Abstract: Biological nitrogen fixation (BNF) is a major nitrogen input pathway in the ecosystem and generates nearly 200 tera gram of organic nitrogen annually. BNF can play an important role both in climate preservation and agriculture sustainability. However, BNF has received lesser attention in farming practices because the synthetic nitrogen fertilizers are inexpensive and easily accessible, and since the cereal crops were not able to forge a symbiotic relationship, remaining dependent on synthetic versions of nitrogen fertilizers. Moreover, BNF is a complex phenomenon governed by the presence of genetic elements in both the host and Rhizobium compared to other allelic traits in crops. The nitrogen supplementation being an essential macronutrient with dramatic effect on productivity was not until recently viewed as a threat to the environment when its effects on greenhouse gas and pollution of aquatic systems clearly became evident. The environmental penalty and questionable sustainability of nitrogen use at the existing and imminently higher levels in future underscore the importance of BNF in sustainability. In-depth understanding of genetic basis of symbiosis and rhizobia host-specificity is crucial to set the stage for considering BNF as one of the breeding priorities. In this review, we bring together recent information from the perspectives of both the host and Rhizobia that should help strengthen the symbiotic partnership of BNF for agricultural sustainability. The environmental factors that significantly impact the symbiosis and determine the performance of a host-rhizobia mutualistic relationship are also reviewed.