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Review
. 2022 Sep 12;3(5):100327.
doi: 10.1016/j.xplc.2022.100327. Epub 2022 Apr 18.

Right time, right place: The dynamic role of hormones in rhizobial infection and nodulation of legumes

Karen Velandia  1 , James B Reid  1 , Eloise Foo  2
Affiliations
Review

Right time, right place: The dynamic role of hormones in rhizobial infection and nodulation of legumes

Karen Velandia et al. Plant Commun. .

Abstract

Many legume plants form beneficial associations with rhizobial bacteria that are hosted in new plant root organs, nodules, in which atmospheric nitrogen is fixed. This association requires the precise coordination of two separate programs, infection in the epidermis and nodule organogenesis in the cortex. There is extensive literature indicating key roles for plant hormones during nodulation, but a detailed analysis of the spatial and temporal roles of plant hormones during the different stages of nodulation is required. This review analyses the current literature on hormone regulation of infection and organogenesis to reveal the differential roles and interactions of auxin, cytokinin, brassinosteroids, ethylene, and gibberellins during epidermal infection and cortical nodule initiation, development, and function. With the exception of auxin, all of these hormones suppress infection events. By contrast, there is evidence that all of these hormones promote nodule organogenesis, except ethylene, which suppresses nodule initiation. This differential role for many of the hormones between the epidermal and cortical programs is striking. Future work is required to fully examine hormone interactions and create a robust model that integrates this knowledge into our understanding of nodulation pathways.

Keywords: auxin; brassinosteroids; cytokinin; ethylene; gibberellin; nodulation.

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Figures

Figure 1
Figure 1
Temporal and spatial sequence of events during nodulation in the cortex and epidermis. (A) Scheme of stages of infection (i–iii) and nodule development and maturation (iv–vi). The timing is based on data from studies in Medicago truncatula. Similar physical changes occur in species such as Lotus japonicus. Red indicates the presence of bacteria. Epi, epidermis. (B) Summary of the roles of plant hormones in stages of infection and nodule development across legume species. Plus sign (+) indicates a positive role, minus (−) indicates a negative role, n.a. indicates not assessed, and (−?) indicates that there is also some evidence for a negative role of the hormone.
See this image and copyright information in PMC

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