The regulatory effect of abscisic acid on colonization and sporulation of arbuscular mycorrhizal fungus

Abstract:

[Objective] To reveal the effects of abscisic acid (ABA) on the colonization and sporulation of arbuscular mycorrhiza (AM) fungi, and to establish a highly efficient propagation methods by promoting spore production with exogenous ABA. [Methods] We established the dual culture system with tomato hairy roots and AM fungus Rhizophagus irregularis DAOM 197198, and the exogenous ABA and gibberellin (GA) were applied, or the deficient mutants of ABA and GA were employed. The mycorrhizal colonization was observed after staining, the expression of genes involved in the development of arbuscules and the synthesis and transfer of lipids were measured with qRCR, and the numbers of arbuscules and spores were counted, in order to reveal the effects of ABA on the colonization and sporulation of AM fungus. [Results] In the ABA-deficient mutant not, F% (mycorrhizal frequency), a% (arbuscular abundance), number of arbuscules, and the expression of arbuscule development-specific gene EXO70A1-like (LOC101253481) and the lipid synthesis and transfer related genes RAM2 and STR2 were significantly lower than those in the wild-type MT. Exogenous application of ABA significantly promoted F%, M% (mycorrhizal intensity), number of arbuscules, spore production, and the expression of RAM2 and STR2. The spore production applied with exogenous ABA was approximately 4.5 times of that without application. Exogenous GA significantly inhibited all parameters of mycorrhizal colonization and spore production. The spore production of GA-deficient mutant gib3 was significantly higher than that of the wild-type MM, although there was no significant difference in mycorrhizal colonization between gib3 and MM. [Conclusion] By promoting the lipid synthesis and transfer, ABA increases the colonization and arbuscular formation of AM fungi, and further enhances AM fungal sporulation.