Microbial biodiversity and structure in soil affects the composition of pyrrolizidine alkaloids in Jacobaea vulgaris. dilution experiment

Secondary metabolites like pyrrolizidine alkaloids (PAs) act as defense compounds against aboveground and belowground attackers. We studied to get a better understanding of relevance of microbial diversity in the rhizosphere for plant growth and behavior, specifically related to secondary metabolites production. We made soil dilution to compare the composition of soil microbial communities of soil suspension, incubation and rhizosphere soil by 16s rRNA high throughput pyrosequencing, as a consequence, to determine the effects on plant behaviors. The dilution procedure leads to reduction of the diversity of bacteria at the phylum level. After regrown, the structure of microbial community in the rhizosphere changed significantly as compared to the composition in the incubated soil. Jacobeae vulgaris as model plants growing in the soil where microbial diversity were decreased, had a higher biomass and higher amount of free base form of PAs’ production, which indicates the reduction of soil microbial community in the rhizosphere shows significant feedback. Our study adds evidence that soil microbes may play a role in the evolution of plant secondary metabolites in plants.

吡咯里西啶生物碱（pyrrolizidine alkaloids, PAs）等次生代谢物可作为防御化合物，抵御植物地上与地下的生物侵害。本研究旨在深入解析根际微生物多样性对植物生长及性状表现的关联作用，特别是与次生代谢物合成相关的调控机制。我们通过土壤稀释梯度实验，结合16S核糖体RNA（16S rRNA）高通量焦磷酸测序技术，对比分析土壤悬浮液、培养土壤与根际土壤的微生物群落组成，进而明确其对植物性状表现的影响。该土壤稀释操作会导致细菌在门水平上的多样性降低。待供试植物定植生长后，根际微生物群落结构相较于培养土壤的群落组成发生了显著改变。以普通千里光（Jacobeae vulgaris）为模式植物，在微生物多样性降低的土壤中生长时，其生物量更高，游离碱型吡咯里西啶生物碱的合成量也显著提升，这表明根际土壤微生物群落的减少会产生显著的反馈效应。本研究为土壤微生物可能参与植物次生代谢物的演化过程提供了新的实验证据。