Casuarina glauca: A model tree for basic research in actinorhizal symbiosis

Abstract

Casuarina glauca is a fast-growing multipurpose tree belonging to the Casuarinaceae family and native to Australia. It requires limited use of chemical fertilizers due to the symbiotic association with the nitrogen-fixing actinomycete Frankia and with mycorrhizal fungi, which help improve phosphorous and water uptake by the root system. C. glauca can grow in difficult sites, colonize eroded lands and improve their fertility, thereby enabling the subsequent growth of more demanding plant species. As a result, this tree is increasingly used for reforestation and reclamation of degraded lands in tropical and subtropical areas such as China and Egypt. Many tools have been developed in recent years to explore the molecular basis of the interaction between Frankia and C. glauca. These tools include in vitro culture of the host and genetic transformation with Agrobacterium, genome sequencing of Frankia and related studies, isolation of plant symbiotic genes combined with functional analyses (including knock-down expression based on RNA interference), and transcriptome analyses of roots inoculated with Frankia or Rhizophagus irregularis. These efforts have been fruitful since recent results established that many common molecular mechanisms regulate the nodulation process in actinorhizal plants and legumes, thus providing new insights into the evolution of nitrogen-fixing symbioses.

Influence of salt stress on inoculated Casuarina glauca seedlings

“…Actinorhizal plants, which form nitrogen-fixing nodules as a result of symbiotic relation with Frankia, can grow and resist harsh conditions and have been used as pioneer plants for soil rehabilitation (Zhong et al 2013;Bogusz et al 2015).…”

Is salt stress tolerance in Casuarina glauca Sieb. ex Spreng. associated with its nitrogen-fixing root-nodule symbiosis? An analysis at the photosynthetic level

“…Ex Spreng. (family Casuarinaceae) originated in the southeastern coastal regions of Australia and is considered an actinorhizal model plant for several reasons (Zhong et al, 2013). First, the availability of a genetic transformation system and the fact that it has a small genome make C. glauca very well suited for basic research.…”

Optimization of the conditions for Casuarina cunninghamiana Miq. genetic transformation mediated by Agrobacterium tumefaciens

“…Developing gene transfer techniques in casuarina trees therefore can contribute to improved tolerance to biotic and abiotic stress of these tree species. Besides, it is an important tool for the basic molecular knowledge of the symbiosis established between Frankia and casuarinas (Svistoonoff et al 2010;Zhong et al 2013).…”