Celebrating 20 Years of Genetic Discoveries in Legume Nodulation and Symbiotic Nitrogen Fixation (REVIEW)

Sonali Roy, Wei Liu, Raja Sekhar Nandety, Ashley Crook, Kirankumar S Mysore, Catalina I Pislariu, Julia Frugoli, Rebecca Dickstein, Michael K Udvardi.

Plant Cell 2020 Jan; 32(1):15-41.  doi: 10.1105/tpc.19.00279. Epub 2019 Oct 24.

Abstract

Since 1999, various forward- and reverse-genetic approaches have uncovered nearly 200 genes required for symbiotic nitrogen fixation (SNF) in legumes. These discoveries advanced our understanding of the evolution of SNF in plants and its relationship to other beneficial endosymbioses, signaling between plants and microbes, the control of microbial infection of plant cells, the control of plant cell division leading to nodule development, autoregulation of nodulation, intracellular accommodation of bacteria, nodule oxygen homeostasis, the control of bacteroid differentiation, metabolism and transport supporting symbiosis, and the control of nodule senescence. This review catalogs and contextualizes all of the plant genes currently known to be required for SNF in two model legume species, Medicago truncatula and Lotus japonicus, and two crop species, Glycine max (soybean) and Phaseolus vulgaris (common bean). We also briefly consider the future of SNF genetics in the era of pan-genomics and genome editing.

See https://pubmed.ncbi.nlm.nih.gov/31649123/

Figure 4.  Rhizobial Infection.

The entry of rhizobia into the plant cell via tubular ITs triggers a transient ROS burst (1). This is accompanied by cell wall degradation (2), membrane remodeling (3), and cytoskeletal rearrangements (4). The IT is led by a complex at its tip called the infectosome (5). In parallel, several other transcriptional and posttranslational changes (6) and the autophagy pathway (7) ensure accommodation of the symbiont within the plant host.