Nodule INception‐independent epidermal events lead to bacterial entry during nodule development in peanut (Arachis hypogaea)

Abstract

Legumes can host nitrogen-fixing rhizobia inside root nodules. In model legumes, rhizobia enter via infection threads (ITs) and develop nodules in which the infection zone contains a mixture of infected and uninfected cells. Peanut (Arachis hypogaea) diversified from model legumes c. 50-55 million years ago. Rhizobia enter through 'cracks' to form nodules in peanut roots where cells of the infection zone are uniformly infected. Phylogenomic studies have indicated symbiosis as a labile trait in peanut. These atypical features prompted us to investigate the molecular mechanism of peanut nodule development.Combining cell biology, genetics and genomic tools, we visualized the status of hormonal signaling in peanut nodule primordia. Moreover, we dissected the signaling modules of Nodule INception (NIN), a master regulator of both epidermal infection and cortical organogenesis.Cytokinin signaling operates in a broad zone, from the epidermis to the pericycle inside nodule primordia, while auxin signaling is narrower and focused. Nodule INception is involved in nodule organogenesis, but not in crack entry. Nodulation Pectate Lyase, which remodels cell walls during IT formation, is not required. By contrast, Nodule enhanced Glycosyl Hydrolases (AhNGHs) are recruited for cell wall modification during crack entry.While hormonal regulation is conserved, the function of the NIN signaling modules is diversified in peanut.

ORM-mediated regulation of sphingolipid biosynthesis is essential for nodule formation inAeschynomene evenia

“…Interestingly, analysis of the AeORM1 expression pattern revealed a constitutive expression at lateral root bases where rhizobial infection and nodule formation occur. This information complements the one recently obtained in the another LRB-nodulating legume, A. hypogaea, for which the expression of the symbiotic genes AhNIN and AhCYCLOPS was found to be induced specifically at lateral root bases upon rhizobial inoculation (Bhattacharjee et al, 2022). In addition, the early abortion of nodule development in the three A. evenia orm1 mutants shows that AeORM1 is essential for lateral root base-nodulation.…”

Plant-Rhizobia Symbiosis and Nitrogen Fixation in Legumes

“…NIN is among the earliest-responding genes to rhizobia inoculation, suggesting its involvement in the initiation of bacterial infection, except rhizobial crack-entry infection in peanut (Arachis hypogaea) Mergaert et al, 2020;Bhattacharjee et al, 2022). NIN loss of function leads to widespread defects in gene expression, highlighting its pivotal role in the gene regulatory network governing rhizobia infection (Liu C.W.…”

NIN—at the heart of NItrogen-fixing Nodule symbiosis

“…NIN is among the earliest-responding genes to rhizobia inoculation, suggesting its involvement in the initiation of bacterial infection, except rhizobial crack-entry infection in peanut (Arachis hypogaea) (Schiessl et al, 2019;Mergaert et al, 2020;Bhattacharjee et al, 2022). NIN loss of function leads to widespread defects in gene expression, highlighting its pivotal role in the gene regulatory network governing rhizobia infection (Liu C.W.…”