Molecular Basis of Root Nodule Symbiosis between Bradyrhizobium and ‘Crack-Entry’ Legume Groundnut (Arachis hypogaea L.)
International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), Hyderabad 502324, India
Department of Biochemistry, University of Calcutta, Kolkata 700019, India
Department of Botany, Sister Nibedita Government General Degree College for Girls, Kolkata 700027, India
Department of Life Sciences, Central University of Karnataka, Kadaganchi-585367, India
DBT-National Agri-food Biotechnology Institute (NABI), Punjab 140308, India
Instituto de Investigaciones Agrobiotecnológicas (CONICET-UNRC), Río Cuarto-5800, Córdoba, Argentina
Agronomy Department, University of Florida, Gainesville, FL 103610, USA
Crop Protection and Management Research Unit, United State Department of Agriculture- Agriculture Research Service (USDA-ARS), Tifton, GA 31793, USA
Author to whom correspondence should be addressed.
Plants 2020, 9(2), 276; https://doi.org/10.3390/plants9020276
Received: 18 December 2019 / Revised: 17 January 2020 / Accepted: 24 January 2020 / Published: 20 February 2020
(This article belongs to the Special Issue Nitrogen-Fixing Plants )
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.