Improved observation of colonized roots reveals the regulation of arbuscule development and senescence by drought stress in the arbuscular mycorrhizae of citrus

Citrus is the typical mycorrhizal fruit tree species establishing symbiosis with arbuscular mycorrhizal (AM) fungi. However, arbuscule development and senescence in colonized citrus roots, especially in response to drought stress, remain unclear, which is mainly due to the difficulty in clearing and staining lignified roots with the conventional method. Here, we improved the observation of colonized roots of citrus plants with the sectioning method, which enabled the clear observation of AM fungal structures. Furthermore, we investigated the effects of one week of drought stress on arbuscule development and senescence with the sectioning method. Microscopy observations indicated that drought stress significantly decreased mycorrhizal colonization (F%and M%) although it did not affect plant growth performance. Fluorescence probes (WGA 488 and/or Nile red) revealed that drought stress inhibited arbuscule development by increasing the percentage of arbuscules at the early stage and decreasing the percentages of arbuscules at the midterm and mature stages. Meanwhile, drought stress accelerated arbuscule senescence, which was characterized by the increased accumulation of neutral lipids. Overall, the sectioning method developed in this study enables the in-depth investigation of arbuscule status, and drought stress can inhibit arbuscule development but accelerate arbuscule senescence in the colonized roots of citrus plants. This study paves the way to elaborately dissecting the arbuscule dynamics in the roots of fruit tree species in response to diverse abiotic stresses.

Quantum Dot Nanobeads-Labelled Lateral Flow Immunoassay Strip for Rapid and Sensitive Detection of Salmonella Typhimurium Based on Strand Displacement Loop-Mediated Isothermal Amplification

Rapid,sensitive,point-of-care detection of pathogenic bacteria is important for food safety.In this study,we developed a novel quantum dot nanobeads-labelled lateral flow immunoassay strip(QBs-labelled LFIAS)combined with strand displacement loop-mediated isothermal amplification(SD-LAMP)for quantitative Salmonella Typhimurium(ST)detection.Quantum dot nanobeads(QBs)served as fluorescence reporters,providing good detection efficiency.The customizable strand displacement(SD)probe was used in LAMP to improve the specificity of the method and prevent by-product capture.Detection was based on a sandwich immunoassay.A fluorescence strip reader measured the fluorescence intensity(FI)of the test(T)line and control(C)line.The linear detection range of the strip was 10^(2)–10^(8) colony forming units(CFU)·mL^(-1).The visual limit of detection was 10^(3) CFU·mL^(-1),indicating that the system was ten-fold more sensitive than AuNPs-labelled test strips.ST specificity was analyzed in accordance with agarose gel outputs of polymerase chain reaction(PCR)and SD-LAMP.We detected ST in foods with an acceptable recovery of 85%–110%.The method is rapid,simple,almost equipment-free,and suitable for bacterial detection in foods and for clinical diagnosis.

Structure,variation and assembly processes of bacterial communities in different root-associated niches of tomato under periodic drought and nitrogen addition

Root-associated bacteria play a vital role in the growth and adaptation of host plants to drought stress.These bacteria can be classified as rhizoplane and rhizosphere bacteria based on their distance from the root surface.Tomato plants are often exposed to periodic drought and nitrogen(N)addition throughout their life cycle,but the impacts of these factors on the plant and root-associated bacteria are not well understood.To gain insight into this relationship,we conducted an experiment to monitor the effects of periodic drought and N addition on rhizoplane and rhizosphere bacteria of tomato plants.Drought and N addition had interactive effects on plant and soil properties,which varied with the timing of drought.There were clear divergences in community traits such as alpha diversity,beta diversity,and network topological features between the two types of bacteria.The rhizoplane bacteria showed lower alpha diversity but higher beta diversity and were more sensitive to drought and N addition than the rhizosphere bacteria.Nitrogen addition could downsize the effects of drought on rhizoplane bacterial community compositions.The higher proximity to the root might induce a community to develop more cooperation between different members to cope with plant metabolites,as revealed by the more connected and modularized community network of the rhizoplane bacteria.Drought at the seedling stage had great legacy effects on plant and soil properties.It may enhance selection,cause the dominance of deterministic processes in the assembly of rhizoplane bacteria,and reduce bacterial community network complexity.In conclusion,N addition could interact with drought in affecting tomato plants and their root-associated bacteria,depending on the timing of drought and the fineness of root niches.The higher sensitivity of rhizoplane bacteria to drought and N addition calls for more research due to their higher proximity and importance to plants in future environmental changes.

未/难培养微生物:风正扬帆再起航,共辉煌

“未/难培养微生物”通常是指在环境中存在、但尚未在实验室条件下获得纯培养的微生物统称。微生物是地球上进化历史最长、生物量最大、多样性最丰富的生命形式。这种简单而古老的生命决定了地球演化的方向和进程,参与了生物圈的物质和能量循环,并深刻影响着人类社会发展的历史,在近现代生命科技不断进步的过程中发挥了基础性和关键性作用。

脱落酸对丛枝菌根真菌侵染和产孢的调控效应研究

【目的】揭示脱落酸(ABA)对丛枝菌根(AM)真菌侵染和产孢的影响,建立利用外源ABA促进孢子产量的高效菌剂扩繁方法。【方法】利用番茄毛状根和AM真菌Rhizophagus irregularis DAOM 197198建立双重培养体系,通过外源施用ABA、赤霉素(GA)或者使用ABA、GA的缺陷突变体,染色观察菌根侵染,荧光定量PCR测定丛枝发育和脂质合成运输相关基因的表达,统计丛枝和孢子的数量,从而揭示ABA对AM真菌侵染和产孢的影响。【结果】ABA缺陷突变体not中的F%(侵染频率)、a%(丛枝丰度)、丛枝数量,以及丛枝发育特异性相关基因EXO70A1-like(LOC101253481)、脂质合成运输相关基因RAM2和STR2的表达均显著低于其野生型MT;外源施用ABA显著促进了F%、M%(侵染强度)、丛枝数量、孢子产量,以及脂质合成运输相关基因RAM2和STR2的表达,外源添加ABA处理的孢子产量约为不添加处理的4.5倍;外源GA处理极显著抑制了菌根侵染的所有指标和孢子产量;GA缺陷突变体gib3与其野生型MM的AM真菌侵染之间没有显著差异,但gib3的孢子产量显著高于MM。【结论】ABA通过促进脂质的合成和运输,提高AM真菌的侵染和丛枝形成,进而增加AM真菌的孢子产量。