Molecular Basis of Root Nodule Symbiosis between Bradyrhizobium and ‘Crack-Entry’ Legume Groundnut (Arachis hypogaea L.)
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Date
2024
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Publisher
MDPI
Abstract
Nitrogen is one of the essential plant nutrients and a major factor limiting crop productivity.
To meet the requirements of sustainable agriculture, there is a need to maximize biological nitrogen
fixation in different crop species. Legumes are able to establish root nodule symbiosis (RNS) with
nitrogen-fixing soil bacteria which are collectively called rhizobia. This mutualistic association is
highly specific, and each rhizobia species/strain interacts with only a specific group of legumes,
and vice versa. Nodulation involves multiple phases of interactions ranging from initial bacterial
attachment and infection establishment to late nodule development, characterized by a complex
molecular signalling between plants and rhizobia. Characteristically, legumes like groundnut display
a bacterial invasion strategy popularly known as “crack-entry” mechanism, which is reported
approximately in 25% of all legumes. This article accommodates critical discussions on the bacterial
infection mode, dynamics of nodulation, components of symbiotic signalling pathway, and also
the effects of abiotic stresses and phytohormone homeostasis related to the root nodule symbiosis
of groundnut and Bradyrhizobium. These parameters can help to understand how groundnut RNS
is programmed to recognize and establish symbiotic relationships with rhizobia, adjusting gene
expression in response to various regulations. This review further attempts to emphasize the
current understanding of advancements regarding RNS research in the groundnut and speculates on
prospective improvement possibilities in addition to ways for expanding it to other crops towards
achieving sustainable agriculture and overcoming environmental challenges.