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Review
. 2021 Jan 7;9(1):125.
doi: 10.3390/microorganisms9010125.

Molecular Biology in the Improvement of Biological Nitrogen Fixation by Rhizobia and Extending the Scope to Cereals

Ravinder K Goyal  1 , Maria Augusta Schmidt  1   2 , Michael F Hynes  2
Affiliations
Review

Molecular Biology in the Improvement of Biological Nitrogen Fixation by Rhizobia and Extending the Scope to Cereals

Ravinder K Goyal et al. Microorganisms. .

Abstract

The contribution of biological nitrogen fixation to the total N requirement of food and feed crops diminished in importance with the advent of synthetic N fertilizers, which fueled the "green revolution". Despite being environmentally unfriendly, the synthetic versions gained prominence primarily due to their low cost, and the fact that most important staple crops never evolved symbiotic associations with bacteria. In the recent past, advances in our knowledge of symbiosis and nitrogen fixation and the development and application of recombinant DNA technology have created opportunities that could help increase the share of symbiotically-driven nitrogen in global consumption. With the availability of molecular biology tools, rapid improvements in symbiotic characteristics of rhizobial strains became possible. Further, the technology allowed probing the possibility of establishing a symbiotic dialogue between rhizobia and cereals. Because the evolutionary process did not forge a symbiotic relationship with the latter, the potential of molecular manipulations has been tested to incorporate a functional mechanism of nitrogen reduction independent of microbes. In this review, we discuss various strategies applied to improve rhizobial strains for higher nitrogen fixation efficiency, more competitiveness and enhanced fitness under unfavorable environments. The challenges and progress made towards nitrogen self-sufficiency of cereals are also reviewed. An approach to integrate the genetically modified elite rhizobia strains in crop production systems is highlighted.

Keywords: biological nitrogen fixation; cereals; efficiency; ethylene; improvement; molecular biology; nodulation; rhizobia; stress.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Pathway of ethylene synthesis and reduction in its level through substrate mobilization. S-AdoMet or SAM, S-adenosylmethionine; MTA, Methylthioadenosine; ACC, 1-aminocyclopropane-1-carboxylic acid.
Figure 2
Figure 2
Genetic engineering approaches to improve the availability of biologically fixed nitrogen in cereal crops.
See this image and copyright information in PMC

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