The PAM1 gene of petunia,required for intracellular accommodation and morphogenesis of arbuscular mycorrhizal fungi,encodes a homologue of VAPYRIN

Most terrestrial plants engage into arbuscular mycorrhizal (AM) symbiosis with fungi of the phylum Glomeromycota. The initial recognition of the fungal symbiont results in the activation of a symbiosis signalling pathway that is shared with the root nodule symbiosis (common SYM pathway). The subsequent intracellular accommodation of the fungus, and the elaboration of its characteristic feeding structures, the arbuscules, depends on a genetic programme in the plant that has recently been shown to involve the VAPYRIN gene in Medicaco truncatula. We have previously identified a mutant in Petunia hybrida, penetration and arbuscule morphogenesis 1 (pam1), that is defective in the intracellular stages of AM development. Here, we report on the cloning of PAM1, which encodes a VAPYRIN homologue. PAM1 protein localizes to the cytosol and the nucleus, with a prominent affinity to mobile spherical structures that are associated with the tonoplast, and are therefore referred to as tonospheres. In mycorrhizal roots, tonospheres were observed in the vicinity of intracellular hyphae, where they may play an essential role in the accommodation and morphogenesis of the fungal endosymbiont.     

缺铁和过量重碳酸盐胁迫下丛枝菌根真菌对枳活性氧代谢的影响

采用盆栽沙培试验,研究了缺铁处理及重碳酸盐胁迫下丛枝菌根真菌地表球囊霉对枳实生苗抗活性氧系统的影响。试验结果表明,在缺铁以及重碳酸盐胁迫处理下,丛枝菌根真菌显著提高了枳叶片和根系中可溶性蛋白含量、超氧化物岐化酶活性、过氧化物酶活性和过氧化氢酶活性,明显增强了叶片类胡萝卜素含量,显著降低了枳叶片和根系中的丙二醛含量,增强了枳自身防御能力,减少了胁迫对枳细胞膜的伤害。     

Molecular trait indicators: moving beyond phylogeny in arbuscular mycorrhizal ecology

Arbuscular mycorrhizal (AM) fungi form symbiotic associations with the roots of most plants, thereby mediating nutrient and carbon fluxes, plant performance, and ecosystem dynamics. Although considerable effort has been expended to understand the keystone ecological position of AM symbioses, most studies have been limited in scope to recording organism occurrences and identities, as determined from morphological characters and (mainly) ribosomal sequence markers. In order to overcome these restrictions and circumvent the shortcomings of culture- and phylogeny-based approaches, we propose a shift toward plant and fungal protein-encoding genes as more immediate indicators of mycorrhizal contributions to ecological processes. A number of candidate target genes, involved in the uptake of phosphorus and nitrogen, carbon cycling, and overall metabolic activity, are proposed. We discuss the advantages and disadvantages of future protein-encoding gene marker and current (phylo-) taxonomic approaches for studying the impact of AM fungi on plant growth and ecosystem functioning. Approaches based on protein-encoding genes are expected to open opportunities to advance the mechanistic understanding of ecological roles of mycorrhizas in natural and managed ecosystems.     

海南霸王岭热带雨林常见植物丛枝菌根真菌调查

对海南霸王岭热带雨林的12科16种常见植物的丛枝菌根状况进行了调查,用碱解离-酸性品红染色法进行了真菌鉴定。结果表明,13种植物形成典型的丛枝菌根,占所调查植物的81%;3种植物没有形成丛枝菌根,占所调查植物的19%。用湿筛沉淀法从这些植物根际土壤中共分离鉴定出了3属11种丛枝菌根真菌(AMF),即无梗囊霉属(Acaulos-pora)3种,球囊霉属(Glomus)7种,巨孢囊霉属(Gigaspora)1种;其中,球囊霉属是样地的优势属。在AMF中,孔窝无梗囊霉(A.foveata)分离频率最高,在14种植物的根际土中都有发现;此外,大果球囊霉(G.macrocarpum)的相对多度最大,为59%,具有最强的产孢能力。同时,在11种植物的根中发现了深色有隔内生真菌(DSE),占调查植物的69%;其中,11种植物同时被DSE和AMF感染。     

Phylogenetic relatedness explains highly interconnected and nested symbiotic networks of woody plants and arbuscular mycorrhizal fungi in a Chinese subtropical forest

Elucidating symbiotic relationships between arbuscular mycorrhizal fungi (AMF) and plants contributes to a better understanding of their reciprocally dependent coexistence and community assembly. However, the main drivers of plant and AMF community assembly remain unclear. In this study, we examined AMF communities from 166 root samples of 17 woody plant species from 10 quadrats in a Chinese subtropical forest using 454 pyrosequencing of 18S rRNA gene to describe symbiotic AMF–plant association. Our results show the woody plant–AMF networks to be highly interconnected and nested, but in antimodular and antispecialized manners. The nonrandom pattern in the woody plant–AMF network was explained by plant and AMF phylogenies, with a tendency for a stronger phylogenetic signal by plant than AMF phylogeny. This study suggests that the phylogenetic niche conservatism in woody plants and their AMF symbionts could contribute to interdependent AMF and plant community assembly in this subtropical forest ecosystem.     

丛枝菌根网络对不同喀斯特适生植物生长及氮摄取的影响

丛枝菌根真菌(arbuscular mycorrhizal fungi,AMF)能够通过菌丝体在不同的植物个体间形成公用菌根网(Common mycorrhizal networks,CMN)。针对喀斯特生境中不同植物个体间通过CMN调控营养分配和生物性状的问题,本研究选择了喀斯特生境3种不同的适生植物作为研究对象,模拟自然环境构建微生态系。试验设置同位素供体室和受体室,供体隔室种植香樟并进行同位素~(15)N标记,受体隔室种植不同生长型植物香樟、构树和鬼针草;利用20μm(M~+)和0.45μm尼龙网(M~-)对受体隔室进行处理,同位素~(15)N标记供体植物香樟根系,测定受体植物幼苗叶片δ~(15)N值、植株氮摄取量、生物量以及生长性状指标。试验结果表明:(1)M~+处理的3种受体植物叶片δ~(15)N值分别显著高于M~-处理;同时M~+处理显著提高了香樟幼苗地上、地下部分及植株总氮摄取量,构树和鬼针草的氮摄取量在不同处理间差异未达到显著水平。(2)M~+处理显著提高了香樟地上、地下和总生物量,但对构树没有显著影响;M~+处理下香樟幼苗株高、地径及叶面积和鬼针草幼苗株高、地径分别显著高于M~-处理,但构树在M~+和M~-处理间没有显著差异。(3)M~+处理的香樟幼苗根系平均直径、根长,根表面积和根体积分别显著高于M~-处理,但M~+处理的构树幼苗则显著降低。研究表明,微生态系中丛枝菌根网CMN非平衡性地影响了不同植物个体的氮摄取及植物生长性状,CMN更有利于提高与供体植株为同一物种的受体香樟叶片δ~(15)N、植株N摄取量以及促进其生物量积累和苗木根系生长。     

不同施氮水平下丛枝菌根真菌对藜麦生长和根系生理特征的影响

采用盆栽实验,以藜麦品种‘亿隆1号’为实验材料,探究在不同施氮量(纯氮用分别为0、0.2、0.4和0.6g/kg)接种2种丛枝菌根真菌(AM)即摩西球囊霉(Gm)和扭形球囊霉(Gt)对藜麦及其根系生长指标以及生理指标的影响,为提高氮肥利用率提供理论依据。结果表明:(1)在0.4g/kg施氮量下,接种Gm藜麦根系侵染率和菌根依赖性最大。(2)同一接种处理下,藜麦株高、基径、叶面积、地上部生物量、总根长等根系生长指标,以及根系抗氧化酶活性均随施氮量的增加呈先增加后减小的趋势;与未接种处理相比,接种AM真菌后上述各指标均显著增加,均在0.4g/kg施氮量下达到最大值,且接种Gm的增幅大于接种Gt。(3)同一接种处理下,藜麦根系MDA含量、可溶性糖含量和脯氨酸含量随施氮量的增加均呈先减小后增加的趋势;与未接种处理相比,接种AM真菌后藜麦根系MDA含量显著减小,而其根系可溶性糖含量和脯氨酸含量增加,且接种Gm根系MDA含量降幅以及可溶性糖含量和脯氨酸含量的增幅显著大于接种Gt。研究表明,适量施氮可显著增加藜麦根系摩西球囊霉和扭形球囊霉的侵染率及其菌根依赖性指数,促进藜麦地上部及根系的生长,同时增加其根系抗氧化酶活性和渗透调节物质的积累,减少了体内有害物质的积累,并以摩西球囊霉配合施氮0.4g/kg效果最佳。     

Differential effects of fenpropimorph and fenhexamid, two sterol biosynthesis inhibitor fungicides, on arbuscular mycorrhizal development and sterol metabolism in carrot roots

Sterols composition of transformed carrot roots incubated in presence of increasing concentrations of fenpropimorph (0.02; 0.2; 2 mg l⁻¹) and fenhexamid (0.02; 0.2; 2; 20 mg l⁻¹), colonized or not by Glomus intraradices was determined. In mycorrhizal roots treated with fenpropimorph, normal Δ⁵-sterols were replaced by unusual compounds such as 9β,19-cyclopropylsterols (24-methylpollinastanol), Δ^8,14-sterols (ergosta-8,14-dienol, stigmasta-8,14-dienol), Δ⁸-sterols (Δ⁸ sitosterol) and Δ⁷-sterols (ergosta-7,22-dienol). After application of fenpropimorph, a drastic reduction of the mycorrhizal root growth, root colonization and extraradical fungal development was observed. Application of fenhexamid did not modify sterol profiles and the total colonization of roots. But the arbuscule frequency of the fungal partner was significantly affected.Comparison of the effects caused by the tested fungicides indicates that the usual phytosterols may be involved in symbiosis development. Indeed, observed modifications of root sterols composition could explain the high fenpropimorph toxicity to the AM symbiosis. However, the absence of sterolic modifications in the roots treated with fenhexamid could account for its more limited impact on mycorrhization.