Table1_Screening method and metabolic analysis of plant anti-aging microorganisms via ammonia-induced senescence in the duckweed Wolffia microscopica.docx

Ammonium is the preferred N nutrition over nitrate for some plant species, but it is toxic to many other plant species and induces senescence at high concentrations. The duckweed Wolffia microscopica (Griff.) Kurz is the smallest and fast-growing angiosperm. It is highly sensitive to ammonium and has a short lifespan on media containing 0.5 mM or higher ammonia. This feature makes it a potential model plant to screen for anti-aging microorganisms. By co-culturing W. microscopica with endophytic microorgainisms isolated from rubber tree, we screened out an Aspergillus sclerotiorum strain ITBB2-31 that significantly increased the lifespan and the biomass of W. microscopica. Interestingly, both filter-sterilized and autoclaved exudates of ITBB2-31 increased the lifespan of W. microscopica cultures from 1 month to at least 7 months. Meanwhile, the exudates also showed strong anti-aging effects on cassava and the rubber tree leaves and increased chlorophyll contents by 50% - 350%. However, high contents of filter-sterilized exudates inhibited the growth of W. microscopica while extending its lifespan, indicating that there were heat-sensitive growth-inhibiting agents in the exudates as well. Comparative metabolome analysis of the filter-sterilized and autoclaved exudates revealed multiple heat-stable anti-aging and heat-sensitive growth-inhibiting compounds. Our results suggest that W. microscopica can be served as a rapid and efficient model plant to screen for plant anti-aging microorganisms.

部分植物物种更偏好铵态氮（ammonium）而非硝态氮（nitrate）作为氮营养，但铵态氮对诸多其他植物物种具有毒性，且在高浓度下会诱导植株衰老。显微无根萍（Wolffia microscopica (Griff.) Kurz）是体型最小、生长最快的被子植物，对铵态氮极为敏感，在含0.5 mM及更高浓度氨的培养基中存活周期极短。这一特性使其成为筛选抗衰微生物的潜在模式植物。本研究将显微无根萍与从橡胶树中分离得到的内生微生物共培养，筛选得到一株棘孢曲霉（Aspergillus sclerotiorum）菌株ITBB2-31，该菌株可显著延长显微无根萍的存活周期并提升其生物量。有趣的是，ITBB2-31的滤除菌滤液与高压灭菌胞外分泌物均可将显微无根萍培养物的存活周期从1个月延长至至少7个月。与此同时，该胞外分泌物对木薯及橡胶树叶片同样表现出显著的抗衰效果，可使叶片叶绿素含量提升50%~350%。但高浓度的滤除菌滤液会在延长显微无根萍存活周期的同时抑制其生长，这表明该胞外分泌物中同时存在热敏感型生长抑制物质。对滤除菌滤液与高压灭菌胞外分泌物的比较代谢组学分析显示，其中存在多种热稳定型抗衰物质与热敏感型生长抑制化合物。本研究结果表明，显微无根萍可作为快速高效的模式植物，用于筛选植物抗衰相关微生物。