Legume Genomics and Genetics 2025, Vol.16, No.3, 108-127 http://cropscipublisher.com/index.php/lgg 111 mechanisms that can moderately resist plant defenses to allow themselves to colonize smoothly. In the later stages of nodulation, plants limit the number of nodules through the "autonomous regulation of nodulation (AON)" mechanism: the signal produced by the already formed nodules is transmitted through the aboveground part to inhibit the occurrence of new nodules, so as to avoid the formation of too many nodules and waste host resources. Environmental signals such as nitrate nitrogen also regulate nodulation through this pathway: when the external nitrogen is sufficient, nitrate can act as a signal to upregulate negative regulatory factors in plants (such as NIN-like protein transcription factors, etc.), thereby inhibiting nodule formation and nitrogen fixation to save plant energy. Luo and Xie (2019) summarized the mechanism by which nitrate inhibits nodule symbiosis in two ways: local and systemic, and emphasized the key role of NLP transcription factors and AON pathways. Figure 1 a, b: A soil microcosm system containing microbial and root compartments was established to determine whether Ph. liquidambaris networks transfer rhizobia to the rhizosphere of peanut. The microbial and root compartments were separated by a sterile 30 μm mesh. Roots were confined to the root soil, but fungi and rhizobia in the microbial soil were able to cross the mesh and enter root soil. The treatments with peanut cultivation contained individual seedling planted in root compartment. Sterile 0.45 μm mesh in soil microcosm was used to observe Ph. Liquidambaris-Bradyrhizobium interaction. c: Microcosms were placed in transparent boxes with closed lids to minimize water evaporation and avoid microbial contamination. d: 16S rRNA, nodC, and recA copies in the rhizosphere soil of peanut. At 15 dai, rhizosphere soil of peanut was collected to determine the copy numbers of 16S rRNA, nodC, and recA when the microbial compartment was inoculated with soil suspension with or without Ph. liquidambaris. Data and error bars are the mean ± SE (n = 4). CFUs colony-forming units; dai days after inoculation; IS inoculation site (Adopted from Zhang et al., 2020)
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