SOD1-Targeted Gene Disruption in the Ericoid Mycorrhizal Fungus Oidiodendron maius Reduces Conidiation and the Capacity for Mycorrhization

Abstract

The genome sequences of mycorrhizal fungi will provide new opportunities for studying the biology and the evolution underlying this symbiotic lifestyle. The generation of null mutants at the wild-type loci is one of the best methods for gene-function assignment in the post-genomic era. To our knowledge, the generation of superoxide dismutase 1 (SOD1)-null mutants in the ericoid mycorrhizal fungus Oidiodendron maius is the first example of a gene-targeted disruption via homologous recombination in a mycorrhizal fungus. The disruption of OmSOD1 by Agrobacterium-mediated transformation resulted in the presence of oxidative stress markers, even in the absence of external superimposed stresses, and an increased sensitivity to reactive oxygen species (ROS)-generating substances, especially to menadione. A reduction in conidiation and in the percentage of mycorrhization of Vaccinium myrtillus roots was also observed. The latter findings establish the pivotal role of SOD1 as an important factor in the relationship between O. maius and its symbiotic partner. The lack of this ROS-scavenger may cause an imbalance in the redox homeostasis during host colonization and an alteration in the delicate dialogue between the fungus and its host plant.

Characterization of a CuZn superoxide dismutase gene in the arbuscular mycorrhizal fungus Glomus intraradices

“…Involvement of SOD1 in the control of morphogenetic processes has been demonstrated in other fungi, such as Neurospora crassa (Munkres 1992; Belozerskaya and Gessler 2006), S. cerevisiae (Liu et al 1992) and, more recently, in the ericoid mycorrhizal fungus O. maius (Abbà et al 2009). A significant decrease in conidiation was in fact observed in the O. maiusSOD1-null mutant.…”

“…Overall these data indicate that SOD1 expression is strongly induced in the intraradical phase of the fungus, irrespective of the plant species and fungus involved in the association. Although the precise role of this enzyme in the symbiosis remains to be ascertained, it is likely that it plays a pivotal role in the relationship of the fungus with its host plant, as it has been recently described in the ericoid mycorrhizal fungus O. maius (Abbà et al 2009). A significant decrease in the percentage of mycorrhization was in fact observed in roots colonized by the O. maiusSOD1-null mutant.…”

Symbiosis with an endobacterium increases the fitness of a mycorrhizal fungus, raising its bioenergetic potential

“…This result demonstrates that the bacterium itself does not cooperate with the fungus in ROS detoxification after H 2 O 2 /GR24 treatment, but its presence and its constitutively expressed ROS-related genes contribute to the ROS homeostasis of G. margarita. A regulated synthesis of ROS has a role not only in plant communication (Gilroy et al, 2014), but also in fungal morphogenesis, growth and development, as suggested for fungi interacting with plants or animals (Abbà et al, 2009;Ryder et al, 2013;Mu et al, 2014).…”

Reactive oxygen species metabolism and plant-fungal interactions

“…Although antioxidation activity in plants has been measured during these symbiotic relationships, less attention has been placed on understanding the roles of antioxidation enzymes and genes in the fungal partners. In the ericoid mycorrhizal fungus Oidiodendron maius loss of SOD1 activity in the fungus increased ROS sensitivity and, importantly, reduced the capacity for the fungus to colonize host roots, suggesting redox homeostasis is important for mycorrhization (Abbà et al, 2009). It is thus important to continue to tease apart the arsenal of genes required to successfully colonize plants through molecular analysis.…”