Fast track in vitro mycorrhization of potato plantlets allow studies on gene expression dynamics

Root colonization by arbuscular mycorrhizal (AM) fungi is a dynamic process involving major changes in plant gene expression. Here, the expression of a phosphate transporter gene (PT3) and several defense genes, already known to be involved in the various stages of AM establishment, were monitored in the mycelium donor plant (MDP) in vitro culture system associating potato plantlets with an AM fungus. This system allows fast and homogenous mycorrhization of seedlings at their early stage of development by growing the plantlets in active mycelial networks, but has never been validated for gene expression analysis. Here, QRT-PCR analyses were conducted in parallel to pre- (1 day), early (2 and 3 days), and late (6, 9, and 15 days) stages of root colonization. We observed the induction of a plant gene marker of AM root colonization (PT3) at the late stage and the induction of MAPK and PAL genes at the early and late stages of root colonization. We also demonstrated the induction of PR1 and PR2 genes at pre- and late stages and of GST1 and Lox genes at a late stage of root colonization. These results validated the MDP in vitro culture system as an optimal tool to study gene expression analysis during the AM fungi establishment. This system further opened the door to investigate gene networks associated with the plants–AM fungi symbiosis.     

水稻OsWRKY转录因子对非生物胁迫响应的重叠表达特性分析

WRKY转录因子是植物一类比较大的基因家族,在水稻中已鉴定出102个成员。研究表明WRKY转录因子在植物生长发育、抗病耐逆等方面都具有重要的作用。本研究利用基因芯片数据结合实时定量分析,对水稻Os WRKY转录因子基因在不同的非生物逆境下的表达进行了分析,发现至少有33个Os WRKY基因同时对任何两种非生物胁迫因子做出响应,且所选20个基因中,13个基因可被ABA所诱导。OsWRKY基因这种重叠表达的特性,预示着这些基因在非生物逆境中具有功能多效性,对于培育抗逆境水稻品种具有重要的理论与实践意义。     

Expression profiling of up-regulated plant and fungal genes in early and late stages of<Emphasis Type="Italic"> Medicago truncatula-Glomus mosseae</Emphasis> interactions

Suppression subtractive hybridization (SSH), expression profiling and EST sequencing identified 12 plant genes and six fungal genes that are expressed in the arbuscular mycorrhizal symbiosis between Medicago truncatula and Glomus mosseae. All the plant genes and three of the fungal genes were up-regulated in symbiotic tissues. Expression of 15 of the genes is described for the first time in mycorrhizal roots and two are novel sequences. Six M. truncatula genes were also activated during appressorium formation at the root surface, suggesting a role in this early stage of mycorrhiza establishment, whilst the other six plant genes were only induced in the late stages of mycorrhization and could be involved in the development or functioning of the symbiosis. Phosphate fertilization had no significant influence on expression of any of the plant genes. Expression profiling of G. mosseae genes indicated that two of them may be associated with appressorium development on roots and one with arbuscule formation or function. The other three fungal genes were expressed throughout the life-cycle of G. mosseae.     

Polyploidy in tomato roots as affected by arbuscular mycorrhizal colonization

Nuclear changes in roots of tomato (Lycopersicon esculentum), a plant with a small genome, during the establishment of arbuscular mycorrhizal (AM) colonization were studied using light and electron microscopy, as well as flow and static cytometry. Nuclei of mycorrhizal root cortex cells were larger and had more decondensed chromatin than those of controls. Significant ploidy distribution differences were observed between nuclei of AM colonized and control roots, and a strong correlation between nuclear polyploidization and AM colonization was found. Polyploidization and decondensation are usually associated with high metabolic activity. The metabolic activity of mycorrhizal root cells, evaluated in this work as respiratory activity by using a cytochemical assay for succinate dehydrogenase combined with image analysis, increased in comparison to controls. The meaning of polyploidization is discussed in relation to the structural and metabolic modifications induced by mycorrhization.     

AM真菌摩西管柄囊霉对干旱胁迫下枳抗氧化酶基因表达的影响

测定分析了接种丛枝菌根（AM）真菌摩西管柄囊霉Funneliformis mosseae对正常供水与干旱处理的盆栽枳Poncirus trifoliata实生苗生长、活性氧代谢及抗氧化酶基因表达量的影响。结果表明,7周干旱处理显著降低了根系菌根侵染率。接种摩西管柄囊霉显著促进了干旱处理的枳植株生长,增加了根系体积和叶片相对含水量,显著降低了叶片脯氨酸含量,同时也上调了干旱处理的枳叶片精氨酸脱羧酶基因（PtADC1和PtADC2）和超氧化物歧化酶基因（PtFe-SOD和PtMn-SOD）、过氧化物酶基因（PtPOD）和过氧化氢酶基因（PtCAT1）的表达,因而维持了一个相对更低的活性氧水平（如过氧化氢）,有利于增强植株的抗旱性。     

Root colonization and spore abundance of arbuscular mycorrhizal fungi in distinct successional stages from an Atlantic rainforest biome in southern Brazil

The influence of plant functional groups and moderate seasonality on arbuscular mycorrhizal (AM) fungal status (root colonization and spore density) was investigated during 13 consecutive months in a chronosequence of succession in southern Brazil, consisting of grassland field, scrub vegetation, secondary forest and mature forest, in a region of transition from tropical to subtropical zones. AM root colonization and spore density decreased with advancing succession and were highest in early successional sites with grassland and scrub vegetation, intermediary in the secondary forest and lowest in the mature forest. They were little influenced by soil properties, but were sufficiently influenced by the fine root nutrient status and fine root traits among different functional plant groups. AM root colonization and spore density were higher during the favourable plant growth season (spring and summer) than during the less favourable plant growth season (autumn and winter). Spore density displayed significant seasonal variation at all sites, whilst root colonization displayed significant seasonal variation in grassland, scrub and secondary forest, but not in mature forest. The data suggest that (1) different plant functional groups display different relationships with AM fungi, influencing their abundance differentially; (2) plant species from early successional phases are more susceptible to AM root colonization and maintain higher AM sporulation than late successional species; (3) fine root traits and nutrient status influence these AM fungal attributes; and (4) higher AM spore production and root colonization is associated with the season of higher light incidence and temperature, abundant water in soil and higher plant metabolic activity.     

The arbuscular mycorrhizal symbiosis attenuates symptom severity and reduces virus concentration in tomato infected by Tomato yellow leaf curl Sardinia virus (TYLCSV)

The arbuscular mycorrhizal (AM) symbiosis is considered a natural instrument to improve plant health and productivity since mycorrhizal plants often show higher tolerance to abiotic and biotic stresses. However, the impact of the AM symbiosis on infection by viral pathogens is still largely uncertain and little explored. In the present study, tomato plants were grown under controlled conditions and inoculated with the AM fungus Funneliformis mosseae. Once the mycorrhizal colonization had developed, plants were inoculated with the Tomato yellow leaf curl Sardinia virus (TYLCSV), a geminivirus causing one of the most serious viral diseases of tomatoes in Mediterranean areas. Biological conditions consisted of control plants (C), TYLCSV-infected plants (V), mycorrhizal plants (M), and TYLCSV-infected mycorrhizal plants (MV). At the time of analysis, the level of mycorrhiza development and the expression profiles of mycorrhiza-responsive selected genes were not significantly modified by virus infection, thus indicating that the AM symbiosis was unaffected by the presence and spread of the virus. Viral symptoms were milder, and both shoot and root concentrations of viral DNA were lower in MV plants than in V plants. Overall F. mosseae colonization appears to exert a beneficial effect on tomato plants in attenuating the disease caused by TYLCSV.