Molecular Basis of Root Nodule Symbiosis between Bradyrhizobium and ‘Crack-Entry’ Legume Groundnut (Arachis hypogaea L.)

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.

The application of CRISPR/Cas9 in hairy roots to explore the functions of AhNFR1 and AhNFR5 genes during peanut nodulation

“…These NFR genes were named NFR1 and NFR5 in L. japonicus, both encoding LysM-type serine/threonine receptor kinases [19]. The response of legumes to rhizobial infection is initiated by NFRs, and symbiotic receptor kinase (SYMRK) amplifies the NF-perceived signal [14] which activates downstream symbiotic signaling pathway to start the nodule morphogenesis [14,25,26].…”

“…NFs are recognized by membrane lysin motif (LysM) receptor-like kinases (LYK/LYR) of host root epidermal cells, and subsequently stimulate the signal transduction in plant roots to facilitate the rhizobial infection through infection thread (IT) formation and nodule primordia formation [ 12 , 13 ]. The peanut form nodules predominantly with NF-producing Bradyrhizobium strains, but NF mutant Bradyrhizobium was reported to induce nodules in peanut [ 14 , 15 ]. The mode of rhizobial invasion in peanut is known as the “crack-entry” [ 16 , 17 ], which is different from the “root hair” infection path.…”

Developments and Prospects in Imperative Underexploited Vegetable Legumes Breeding: A Review

“…In contrast, legumes are also known to carry some antinutritional factors like lectins, phytic acid, saponins, and vicine [ 9 ]. Moreover, legumes are characterized by their ability to develop in a symbiotic relationship with nitrogen-fixing bacteria and therefore are also used as soil-enriching green manure [ 10 ].…”

Effects of Nitrogen Fertilization on Mycorrhizal Infection, Nodulation and Growth of Phaseolus vulgaris L.

“…This salinity inhibits establishment of the rhizobium-legume symbiosis during various stages of the process and in general the first stages of nodulation (Zahran, 1999). Indeed, the growth of soil rhizobia can be affected by saline stress by restricting root colonization, infection inhibition, nodule production and functioning (Sharma et al, 2020). Two other hypotheses can explain the insignificant number of nodules on the common bean roots.…”