Mechanisms underlying legume–rhizobium symbioses

Abstract

Legumes, unlike most land plants, can form symbiotic root nodules with nitrogen-fixing bacteria to secure nitrogen for growth. The formation of nitrogen-fixing nodules on legume roots requires the coordination of rhizobial infection at the root epidermis with cell division in the cortex. The nodules house the nitrogen-fixing rhizobia in organelle-like structures known as symbiosomes, which enable nitrogen fixation and facilitate the exchange of metabolites between the host and symbionts. In addition to this beneficial interaction, legumes are continuously exposed to would-be pathogenic microbes; therefore the ability to discriminate pathogens from symbionts is a major determinant of plant survival under natural conditions. Here, we summarize recent advances in the understanding of root nodule symbiosis signaling, transcriptional regulation, and regulation of plant immunity during legumerhizobium symbiosis. In addition, we propose several important questions to be addressed and provide insights into the potential for engineering the capacity to fix nitrogen in legume and nonlegume plants.

GmNAC181 promotes symbiotic nodulation and salt tolerance of nodulation by directly regulating GmNINa expression in soybean

“…CLE‐related‐Root Signal 1/2 in Lotus japonicus , RIC1/2 in soybean) and onset of the autoregulation of nodulation signaling, which systemically controls the nodule numbers (Carroll et al ., 1985a,b; Soyano et al ., 2014; Tsikou et al ., 2018; Wang et al ., 2019). Thus, the spatial and temporal regulation of NIN expression and NIN processing is crucial for symbiotic nodulation and N fixation (Schauser et al ., 1999; Marsh et al ., 2007; Clavijo et al ., 2015; Liu et al ., 2019; Bu et al ., 2020; Feng et al ., 2021; Yang et al ., 2022).…”

Nitrate signaling and use efficiency in crops

“…Rhizobia can convert atmospheric N into ammonium for absorption and utilization by legumes, and in turn, rhizobia can obtain nutrients and carbon sources from the plants to maintain growth ( Müller, 2021 ). Advances in our understanding of symbiotic N fixation have been well summarized in several excellent review papers ( Oldroyd et al., 2011 ; Udvardi and Poole, 2013 ; Ferguson et al., 2019 ; Yang et al., 2022 ). However, few genes involved in coordinately regulating NO 3 – signaling and the rhizobial symbiosis have been identified to date.…”

Cytokinin biosynthesis in cyanobacteria: Insights for crop improvement

“…Infection and nodule organogenesis are the concern of early nodulin genes while the nodule function, maintenance of the oxygen level by leghaemoglobin, etc., are regulated by the products of late nodulin genes (Lebedeva et al, 2021). Cytokinin is responsible for inducing the expression of early nodulin genes in legumes, cortical cell division, and ultimately, the formation of a nodulin-like structure (Yang et al, 2022). Mens et al (2018) studied the role of cytokinin in the nodulation of soybean plants.…”