Lansiumamide B induced the degradation of polysaccharides and oligosaccharides showing antifungal activity against Rhizoctonia solani

Lansiumamide B (LB) is a cinnamamide alkaloid isolated from Clausena lansium seeds. The compound is the main antifungal ingredient found in C. lansium. In this paper, the antifungal activity of LB against 10 plant pathogenic fungi was evaluated and found that it was the most effective to Rhizoctonia solani (EC50 = 2.99 μg/mL). The compound also exhibits certain protective (53.06%) and curative (71.01%) activities against R. solani at 800 μg/mL. The mechanism of action of LB was further elucidated through physiological and biochemical experiments, mycelial morphology and ultrastructure observations, and transcriptomics studies with R. solani as the experimental strain. SEM and TEM observation showed that it caused abnormal mycelium growth, extravasation of contents and cell wall degradation. Physiological and biochemical tests showed that LB treatment had no significant effect on the cellular respiration of mycelium, but it could increase the membrane permeability, cause the leakage of intracellular electrolyte, reduce the content of extracellular polysaccharide and chitin in cell wall and increased the contents of intracellular reducing sugar. The results of transcriptome sequencing analysis showed that LB had significant effects on polysaccharide and oligosaccharide related metabolic pathways, such as starch and sucrose metabolic pathways, galactose metabolic pathways, and amino sugar metabolic pathways. Furthermore, LB treatment increased the specific enzyme activity of α-1, 4-glucanase, α-1,6-glucanase, cellulase and maltase of R. solani in vivo. Comprehensive analysis of the above experimental results shows that LB induces and regulates the degradation of polysaccharides and oligosaccharides of R. solani at the transcriptional level, thereby destroying the cell wall structure and ultimately leading to the death of fungi.