The Actinorhizal Symbiosis

  title={The Actinorhizal Symbiosis},
  author={Luis Gabriel Wall},
  journal={Journal of Plant Growth Regulation},
  • L. Wall
  • Published 1 June 2000
  • Biology
  • Journal of Plant Growth Regulation
A bstractThe term ``actinorhiza'' refers both to the filamentous bacteria Frankia, an actinomycete, and to the root location of nitrogen-fixing nodules. Actinorhizal plants are classified into four subclasses, eight families, and 25 genera comprising more than 220 species. Although ontogenically related to lateral roots, actinorhizal nodules are characterized by differentially expressed genes, supporting the idea of the uniqueness of this new organ. Two pathways for root infection have been… 

Actinorhizal symbioses : diversity and biogeography

The actinobacterial genus Frankia encompasses sporulating filamentous bacteria (actinomycetes) that fix N2; they are defined by their ability to induce N2-fixing root nodules on a broad range of

CHAPTER 7 – Actinorhizal symbioses

Molecular Methods for Research on Actinorhiza

An inventory of the main recent molecular tools and techniques developed for studying actinorhizae is reported, mainly linked to the woody nature of the plant species and the lack of genetic tools for their bacterial symbionts.

Induction of Actinorhizal Nodules by Frankia

An overview of infection mechanisms and nodule structure is given; comparisons with the corresponding mechanisms in legume–rhizobia symbioses are presented.

Establishment of Actinorhizal Symbioses

This chapter summarises the current knowledge of the signalling mechanisms and cellular events that occur during the establishment of actinorhizal symbioses, and describes what is known about the signal exchanges occurring prior to infection.

Actinorhizal nitrogen fixing nodules: infection process, molecular biology and genomics

With progress in plant genome sequencing, comparative genomics in legumes and actinorhizal plants should contribute to the understanding of the evolutionary history of nitrogen-fixing symbioses.

Composite Actinorhizal Plants with Transgenic Roots for the Study of Symbiotic Associations with Frankia

A gene transfer system based on Agrobacterium rhizogenes that opens the possibility to rapidly analyze the function of candidate symbiotic genes is reviewed and the potential of this technique to advancing the understanding of the molecular mechanisms underlying infection by Frankia is demonstrated by functional analyses of symbiosis genes.

Biology of the Frankia-Alnus maritima subsp. maritima symbiosis

If nitrogen fixation is sustained under unfavorable conditions, woody plants that associate with nitrogenfixing organisms may show enhanced tolerance of environmental stress; species of plants capable of nitrogen-fixing symbioses are known to have comparatively strong resistance to invasion by pathogens.

Transformed Hairy Roots of the actinorhizal shrub Discaria trinervis: a valuable tool for studying actinorhizal symbiosis in the context of intercellular infection

To decipher the molecular mechanisms underlying intercellular infection with Frankia, this work set up an efficient genetic transformation protocol for D. trinervis based on A. rhizogenes, an actinorhizal shrub belonging to the Rosales order.

Signalling in actinorhizal root nodule symbioses

This review provides an outline on signalling molecules involved at different stages of actinorhizal nodule formation and the corresponding signalling pathways and gene networks.



Biology of Frankia strains, actinomycete symbionts of actinorhizal plants.

Sufficient information about the relationship of Frankia strains to other bacteria, and to each other, is now available to warrant the creation of some species based on phenotypic and genetic criteria.

Actinorhizal Symbioses : Recent Advances in Plant Molecular and Genetic Transformation Studies

The amino acid sequence derived from the nucleotide sequence of the cDNAs showed that gene products are involved in nitrogen, carbon, and oxygen metabolism and some transcripts represented encoded gene products that might be part of infection and senescence mechanisms in actinorhiza.

Rhizobial and Actinorhizal Symbioses: What Are the Shared Features?

This review discusses the recent progress in research on endophytic symbioses involving plant roots, special attention is given to nitrogen-fixing symbiotic interactions, and the current knowledge of nodule formation and function is summarized.

Natural Diversity of Frankia Strains in Actinorhizal Root Nodules from Promiscuous Hosts in the Family Myricaceae

Actinorhizal plants invade nitrogen-poor soils because of their ability to form root nodule symbioses with N2-fixing actinomycetes known as Frankia, and it is found that strain evenness varies greatly between the plant species so that estimating total strain richness of Frankia within myricaceous nodules with the sample size used was problematical.

Differential gene expression in an actinorhizal symbiosis: evidence for a nodule-specific cysteine proteinase.

Northern hybridization results indicate that this gene may have been recruited for a role specific to this symbiosis, and complexity of hybridization patterns revealed by Southern blot analysis suggests that the gene for AgNOD-CP1 is a member of a multigene family.

Mycorrhizae of actinorhizal plants

To establish an efficient triple symbiosis consideration must be given to endophyte specificity and genetic variability, inoculation regimes and environmental factors, and the importance of a mycorrhizal association in relation to the resistance of certain actinorhizal plants to water stress and to pathogens will be discussed.

Characterization of an ineffective actinorhizal microsymbiont, Frankia sp. EuI1 (Actinomycetales).

Cross-inoculation studies indicated that the host range of this symbiont is narrow and probably restricted to the Elaeagnaceae, and the morphogenetic block is apparently restricted to vesicle formation.

Phylogenetic relationships among actinorhizal plants. The impact of molecular systematics and implications for the evolution of actinorhizal symbioses

By comparing host phylogenies and recently published bacterial phylogenies, the coevolution of bacterial symbionts with their actinorhizal hosts is considered and it is indicated that symbioses have probably arisen more than once.

Casuarina glauca prenodule cells display the same differentiation as the corresponding nodule cells.

The findings indicate that prenodules represent primitive symbiotic organs whose cell types display the same characteristics as their nodule counterparts, and are discussed in the context of the evolution of root nodule symbioses.