Involvement of Root Hair during <i>Rhizobial</i> Invasion in Cultivated Peanut (<i>Arachis hypogaea</i> L.)

Abstract

Peanut root invasion by Bradyrhizobia is through a crack entry, which is different from many other legumes applying an infection thread entry in root hair. Understanding the role of root hair in the crack entry of Bradyrhizobia invasion of peanut root and subsequent peanut nodulation would facilitate improvement of biological nitrogen fixation in cultivated peanut. The objective of this study was to investigate the involvement of root hair in Bradyrhizobial invasion of peanut. Seedling roots of a nodulating peanut cultivar were observed for root hair emergence, its life span, and nodule formation at the base of the lateral roots with and without rhizobia inoculation for 14 days after germination (DAG). Scanning electron microscopy (SEM) was utilized to observe rhizobia accumulation at lateral roots at 24 hours after inoculation (HAI) before the emergence of root hair. Root hair emerged at 7 DAG with or without rhizobia inoculation. Two variations of rosette hair (RoH) were observed, the transient-thin RoH had life span of 3 days after root hair emergence and the thick and densely distributed RoH type stayed till the time of nodule emergence (9 days after inoculation). The lateral root devoid of root hair at the top 2 cm region was found to produce nodules. The SEM observation of seedling roots at 24 HAI showed that Bradyrhizobia invaded the roots at epidermis, protoplasm of cortical cell, and cortical cells of the main root near the newly emerged lateral root in the absence of RoH. The observations validated that root hair is not required in the Bradyrhizobia invasion of peanut root in the crack entry mode. Results from this study provided important morphological information for the hypothesis of close relationship between How to cite this paper: Maku, J., Wang, L.P., Liu, F.X., Liu, L.X., Kelley, K., Peng, Z.

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

“…At 0, 2, 4, 6, 8, 16, 24, 48, 72, 96 and 144 h after inoculation (HAI), the middle 2-3 cm of the primary root was cut from treated plants and immediately put into liquid nitrogen for RNA extraction. The middle 2-3 cm of the peanut primary root at 6 days after germination harbors the active rhizobial infection sites, where the lateral roots are about to emerge [16,17].…”

“…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. The rhizobia enter the root through the middle lamella between adjacent axillary hair cells and invade into the cortex intercellularly.…”

Taxonomic and functional diversity of the soil microbiome recruited from alternative crops in a rotation system

“…The different crop residues and root exudates associated with crop rotation can stimulate the decomposition of organic matter and increase the mineralization of organic phosphorus (Yu et al, 2021). Lukowiak et al (2016) examined phosphorus management in winter rapeseed, silage/grain maize and winter wheat‐based crop rotations and found that crop rotation improved nutrient use and decreased the demand for external sources of P. No functional genes of nitrogen fixation were found in this study, even in the spring peanut→winter wheat‐summer maize rotation system, which was probably because the rhizosphere soil was not involved in this study (Maku et al, 2018). Spring peanut→winter wheat‐summer maize and winter wheat‐summer peanut→winter wheat‐summer maize increased the abundance of nitrate reductase genes ( nar G, Z, H, Y, J, W, I and V ) than that in the control setup.…”