Endophytic fungus-suspension cell co-culture: A new strategy for more rapid and sustainable screening of plant beneficial microorganisms

Microbial fertilizers are increasingly used as alternatives to conventional fertilizers, while the screening process for beneficial microorganisms is inefficient and time-consuming, often taking months or years. This study aimed to evaluate whether the endophytic fungus-suspension cell co-culture strategy could be used for rapid screening of plant beneficial microorganisms. Therefore, we investigated the effects and molecular mechanisms of Fusarium oxysporum GU-7 and GU-60 on the growth and accumulation of secondary metabolites in Glycyrrhiza uralensis suspension cells and potted seedlings. GU-7 significantly promoted the growth of suspension cells and potted seedlings, which may be related to its strong phosphorus-solubilizing and indole-3-acetic acid production capacity. In contrast to GU-60, GU-7 promoted the accumulation of flavonoids and glycyrrhizin at different co-culture times and growth times. Both strains accelerated the accumulation of liquiritigenin, liquiritin, and glycyrrhizin in suspension cells after 24 h of co-culture. Meanwhile, they differentially altered the expression of critical genes. The defense response of suspension cells was enhanced at 72 h, the antioxidant enzyme activity and flavonoid aglycone content were increased and the flavonoid glycoside content was decreased. RNA-seq revealed that the two strains had five times as many glycoside hydrolases as glycosyltransferases and differed in biological processes and biosynthetic pathways involved. Conclusively, the effects of these two strains on suspension cells were consistent with those on potted seedlings, while different strains produced different effects. These results suggest that co-culture with suspension cells is a promising strategy for rapid screening of beneficial microorganisms, even for conspecific fungi. GU-7 has the potential to be further developed as a microbial fertilizer to improve the growth and secondary metabolite accumulation of cultivated licorice.