AM真菌提高烟草钾含量机制的初步研究

以烟草和AM真菌菌株摩西球囊霉（Glomous mosseae,G.m）为材料,研究了不同外界K＋浓度条件下AM真菌对烟草生长、K＋含量以及根中K＋-通道基因NtKT1、NtKT2和转运体基因NtHAK1、NtHA1相对表达量的影响。结果表明,在低钾和常钾条件下,接种G.m均可提高烟草的株高,增加根系长度,提高烟草根部和叶片中的K＋含量,在低钾条件下接种G.m使烟草根部和叶片的K＋含量分别提高了50.5%和24.5%。在常钾条件下,接种G.m 50 d后烟草根系中NtKT1和NtKT2的相对表达量显著提高;而低钾条件下,钾转运体基因NtHAK和NtHA1的相对表达量显著升高。由此推测,AM真菌能够调控烟草根中K＋-通道基因和钾转运体基因的表达进而促进其对K＋的吸收。     

The expression of GintPT, the phosphate transporter of Rhizophagus irregularis, depends on the symbiotic status and phosphate availability

The development of mutualistic interactions with arbuscular mycorrhizal (AM) fungi is one of the most important adaptation of terrestrial plants to face mineral nutrition requirements. As an essential plant nutrient, phosphorus uptake is acknowledged as a major benefit of the AM symbiosis, but the molecular mechanisms of its transport as inorganic phosphate (Pi) from the soil to root cells via AM fungi remain poorly known. Here we monitored the expression profile of the high-affinity phosphate transporter (PT) gene (GintPT) of Rhizophagus irregularis (DAOM 197198) in fungal structures (spores, extraradical mycelium and arbuscules), under different Pi availability, and in respect to plant connection. GintPT resulted constitutively expressed along the major steps of the fungal life cycle and the connection with the host plant was crucial to warrant GintPT high expression levels in the extraradical mycelium. The influence of Pi availability on gene expression of the fungal GintPT and the Medicago truncatula symbiosis-specific Pi transporter (MtPT4) was examined by qRT-PCR assay on microdissected arbusculated cells. The expression profiles of both genes revealed that these transporters are sensitive to changing Pi conditions: we observed that MtPT4 mRNA abundance is higher at 320 than at 32 μM suggesting that the flow towards the plant requires high concentrations. Taken on the whole, the findings highlight novel traits for the functioning of the GintPT gene and offer a molecular scenario to the models describing nutrient transfers as a cooperation between the mycorrhizal partners.     

A constitutive expressed phosphate transporter, OsPht1;1, modulates phosphate uptake and translocation in phosphate-replete rice

A number of phosphate (Pi) starvation- or mycorrhiza-regulated Pi transporters belonging to the Pht1 family have been functionally characterized in several plant species, whereas functions of the Pi transporters that are not regulated by changes in Pi supply are lacking. In this study, we show that rice (Oryza sativa) Pht1;1 (OsPT1), one of the 13 Pht1 Pi transporters in rice, was expressed abundantly and constitutively in various cell types of both roots and shoots. OsPT1 was able to complement the proton-coupled Pi transporter activities in a yeast mutant defective in Pi uptake. Transgenic plants of OsPT1 overexpression lines and RNA interference knockdown lines contained significantly higher and lower phosphorus concentrations, respectively, compared with the wild-type control in Pi-sufficient shoots. These responses of the transgenic plants to Pi supply were further confirmed by the changes in depolarization of root cell membrane potential, root hair occurrence, (33)P uptake rate and transportation, as well as phosphorus accumulation in young leaves at Pi-sufficient levels. Furthermore, OsPT1 expression was strongly enhanced by the mutation of Phosphate Overaccumulator2 (OsPHO2) but not by Phosphate Starvation Response2, indicating that OsPT1 is involved in the OsPHO2-regulated Pi pathway. These results indicate that OsPT1 is a key member of the Pht1 family involved in Pi uptake and translocation in rice under Pi-replete conditions.     

磷有效性对大豆菌根侵染的调控及其与根构型、磷效率的关系

以30个不同根构型的大豆基因型为材料,通过盆栽试验,研究了生长介质磷有效性对大豆接种摩西球囊霉属丛枝菌根真菌的影响及其与根构型、磷效率的关系.结果表明：生长介质磷有效性显著地影响大豆菌根真菌的接种效果.低磷条件下接种菌根真菌效果明显,菌根侵染率较高,菌根对大豆磷吸收的贡献率较大;高磷条件下接种菌根真菌效果不显著,菌根侵染率较低,菌根对大豆磷吸收的贡献率较低.磷有效性和大豆根构型对菌根真菌接种的影响具有交互作用.低磷条件下,中间型和深根型大豆的菌根侵染率最高,浅根型最小.高磷条件下,根构型与菌根侵染率间的关系不明显.根构型和菌根侵染状况对大豆磷效率的贡献存在互利互补关系,磷效率高的大豆基因型一般具有较好的根构型或较高的菌根侵染率.     

Characterization of the phosphate starvation-induced glycerol-3-phosphate permease gene family in Arabidopsis

Phosphate (Pi) deficiency is one of the leading causes of loss in crop productivity. Plants respond to Pi deficiency by increasing Pi acquisition and remobilization involving organic and inorganic Pi transporters. Here, we report the functional characterization of a putative organic Pi transporter, Glycerol-3-phosphate permease (G3Pp) family, comprising five members (AtG3Pp1 to -5) in Arabidopsis (Arabidopsis thaliana). AtG3Pp1 and AtG3Pp2 showed 24-and 3-fold induction, respectively, in the roots of Pi-deprived seedlings, whereas Pi deficiency-mediated induction of AtG3Pp3 and -4 was evident in both roots and shoots. Furthermore, promoter-β-glucuronidase (GUS) fusion transgenics were generated for AtG3Pp2 to -5 for elucidation of their in planta role in Pi homeostasis. During Pi starvation, there was a strong expression of the reporter gene driven by AtG3Pp4 promoter in the roots, shoots, anthers, and siliques, whereas GUS expression was specific either to the roots (AtG3Pp3) or to stamens and siliques (AtG3Pp5) in other promoter-GUS fusion transgenics. Quantification of reporter gene activities further substantiated differential responses of AtG3Pp family members to Pi deprivation. A distinct pattern of reporter gene expression exhibited by AtG3Pp3 and AtG3Pp5 during early stages of germination also substantiated their potential roles during seedling ontogeny. Furthermore, an AtG3Pp4 knockdown mutant exhibited accentuated total lateral root lengths under +phosphorus and -phosphorus conditions compared with the wild type. Several Pi starvation-induced genes involved in root development and/or Pi homeostasis were up-regulated in the mutant. A 9-fold induction of AtG3Pp3 in the mutant provided some evidence for a lack of functional redundancy in the gene family. These results thus reflect differential roles of members of the G3Pp family in the maintenance of Pi homeostasis.     

Arsenic tolerance in a Chlamydomonas photosynthetic mutant is due to reduced arsenic uptake even in light conditions

Arsenate resistance has been used for screening for photosynthetic mutants of Chlamydomonas, since photosynthetic mutants, such as CC981 defective in phosphoribulokinase, were shown to have arsenate resistance. Also, another type of arsenate-resistant mutants, including AR3 that lacks a homolog of a phosphate (Pi) transporter, PTB1, has been isolated. We investigated the uptake of Pi and arsenate, and the gene expression of Pi transporters, which are involved in both Pi and arsenate transport, in mutants CC981 and AR3. In the wild type, both Pi and arsenate uptake were initially high, but were inactivated in the presence of arsenate with time, especially in the dark. In contrast, both mutants were shown to exhibit higher Pi uptake, but lower arsenate uptake than the wild type, regardless of the presence or absence of light. Then, the gene expression of Pi transporters in the cells used for the uptake measurements was investigated and compared between the mutants and the wild type. In CC981, the mRNA levels of PTA2 and PTA4 were higher, while those of PTB3 and PTB5 were lower, as compared with in the wild type. In AR3, those of PTA2 and PTB2 were higher, but that of PTB5 was lower than in the wild type. These findings suggest that the arsenate resistance shown by the mutants in light is due to reduction of arsenate uptake probably through the down-regulation of some Pi transporter expression, while the Pi uptake maintained even in the dark is possibly related to higher expression of other Pi transporter(s) than in the wild type.     

Contribution of six arbuscular mycorrhizal fungal isolates to water uptake by Lactuca sativa plants under drought stress

It is currently accepted that, along with nutrients, arbuscular mycorrhizal (AM) fungi also transport water to their host plant. However, the quantity of water supplied and its significance for plant water relations remain controversial. The objective of this work was to evaluate and compare the ability of six AM fungi to alter rates of root water uptake under drought stress conditions. Soil drying rates of uninoculated control plants of comparable size and nutritional status and mycorrhizal plants were recorded daily. Lactuca sativa plants colonized by Glomus coronatum , G. intraradices , G. claroideum and G. mosseae depleted soil water to a higher extent than comparably sized uninoculated control plants or plants colonized by G. constrictum or G. geosporum . The differences ranged from 0.6% volumetric soil moisture for G. mosseae -colonized plants to 0.95% volumetric soil moisture for G. intraradices -colonized plants. These differences in soil moisture were equivalent to 3–4.75 ml plant⁻¹ day⁻¹, respectively, and could not be ascribed to differences in plant size, but to the activity of AM fungi. The AM fungi tested in this study differed in their effectiveness to enhance plant water uptake from soil. This ability seems to be related to the amount of external mycelium produced by each AM fungus and to the frequency of root colonization in terms of live and active fungal structures.     

Cereal phosphate transporters associated with the mycorrhizal pathway of phosphate uptake into roots

A very large number of plant species are capable of forming symbiotic associations with arbuscular mycorrhizal (AM) fungi. The roots of these plants are potentially capable of absorbing P from the soil solution both directly through root epidermis and root hairs, and via the AM fungal pathway that delivers P to the root cortex. A large number of phosphate (P) transporters have been identified in plants; tissue expression patterns and kinetic information supports the roles of some of these in the direct root uptake pathways. Recent work has identified additional P transporters in several unrelated species that are strongly induced, sometimes specifically, in AM roots. The primary aim of the work described in this paper was to determine how mycorrhizal colonisation by different species of AM fungi influenced the expression of members of the Pht1 gene families in the cereals Hordeum vulgare (barley), Triticum aestivum (wheat) and Zea mays (maize). RT-PCR and in-situ hybridisation, showed that the transporters HORvu;Pht1;8 (AY187023), TRIae;Pht1;myc (AJ830009) and ZEAma;Pht1;6 (AJ830010), had increased expression in roots colonised by the AM fungi Glomus intraradices,Glomus sp. WFVAM23 and Scutellospora calospora. These findings add to the increasing body of evidence indicating that plants that form AM associations with members of the Glomeromycota have evolved phosphate transporters that are either specifically or preferentially involved in scavenging phosphate from the apoplast between intracellular AM structures and root cortical cells. Operation of mycorrhiza-inducible P transporters in the AM P uptake pathway appears, at least partially, to replace uptake via different P transporters located in root epidermis and root hairs. Electronic Supplementary Material Supplementary material is available for this article at     

Genetic diversity for mycorrhizal symbiosis and phosphate transporters in rice

Phosphorus(P) is a major plant nutrient and developing crops with higher P-use efficiency is an important breeding goal.In this context we have conducted a comparative study of irrigated and rainfed rice varieties to assess genotypic differences in colonization with arbuscular mycorrhizal(AM) fungi and expression of different P transporter genes.Plants were grown in three different soil samples from a rice farm in the Philippines.The data show that AM symbiosis in all varieties was established after 4 weeks of growth under aerobic conditions and that,in soil derived from a rice paddy,natural AM populations recovered within6 weeks.The analysis of AM marker genes(AM1,AM3,AM14) and P transporter genes for the direct Pi uptake(PT2,PT6) and AM-mediated pathway(PT11,PT13) were largely in agreement with the observed root AM colonization providing a useful tool for diversity studies.Interestingly,delayed AM colonization was observed in the aus-type rice varieties which might be due to their different root structure and might confer an advantage for weed competition in the field.The data further showed that P-starvation induced root growth and expression of the high-affinity P transporter PT6 was highest in the irrigated variety IR66 which also maintained grain yield under P-deficient field conditions.     

丛枝菌根真菌对滨梅扦插苗生根、生长和抗病相关酶活性的影响

研究Glomus mosseae,G.diaphanum和G.etunicatum对滨梅插条生根、生长和抗病相关酶活性的影响.结果表明:G.mosseae侵染导致最高生根百分率(47.6%),最多次生细根(20.4条),最高的根干重(0.26 g),最高的地上部分干重(3.55 g),最高的幼苗高度(51.3 cm)及...