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Beneficial associations between plants and microbes play an important role in both natural and agricultural ecosystems. For example, associations between fungi of the genus Epichloë, and cool-season grasses are known for their ability to increase resistance to insect pests, fungal pathogens and drought. However, little is known about the molecular changes induced by endophyte infection., To study the impact of endophyte infection, we compared the expression profiles, based on RNA sequencing, of perennial ryegrass infected with Epichloë festucae with noninfected plants., We show that infection causes dramatic changes in the expression of over one third of host genes. This is in stark contrast to mycorrhizal associations, where substantially fewer changes in host gene expression are observed, and is more similar to pathogenic interactions. We reveal that endophyte infection triggers reprogramming of host metabolism, favouring secondary metabolism at a cost to primary metabolism. Infection also induces changes in host development, particularly trichome formation and cell wall biogenesis., Importantly, this work sheds light on the mechanisms underlying enhanced resistance to drought and super-infection by fungal pathogens provided by fungal endophyte infection. Finally, our study reveals that not all beneficial plant-microbe associations behave the same in terms of their effects on the host. [ABSTRACT FROM AUTHOR]

• The aim of this work was to disentangle phosphorus status-dependent and -independent effects of arbuscular mycorrhizal fungus (AMF) on leaf morphology and carbon allocation in perennial ryegrass ( Lolium perenne). • To this end, we assessed the P-response function of morphological components in mycorrhizal and nonmycorrhizal plants of similar size. • AMF ( Glomus hoi) stimulated relative P-uptake rate, decreased leaf mass per area (LMA), and increased shoot mass ratio at low P supply. Lower LMA was caused by both decreased tissue density and thickness. Variation in tissue density was almost entirely caused by variations in soluble C, while that in thickness involved structural changes. • All effects of AMF were indistinguishable from those mediated by increases in relative P-uptake rate through higher P-supply rates. Thus the relationships between relative P-uptake rate, leaf morphology and C allocation were identical in mycorrhizal and nonmycorrhizal plants. No evidence was found for AMF effects not mediated by changes in plant P status. [ABSTRACT FROM AUTHOR]

The lateral spread in a steamed lateritic podsol of Glomus fasciculatum (Thaxter sensu Gerd.) Gerd. and Trappe from localized inoculum was examined in two pasture species: Trifoliumsubterraneum L. (subterranean clover) and Lolium rigidum Gaud. (Wimmera ryegrass). Mycorrhizal infection was estimated 21, 28, 38 and 59 d after sowing at points 2,4,6,8,10, 14, 20 and 26 cm from the inoculum. The proportion of root length infected by G. fasciculatum at increasing distances from the inoculum could be best described by a Gompertz curve in both plant species at all harvests. Thus the curve had an upper plateau of the maximum percentage of infection. It is suggested that the pattern of spread of G. fasciculatum through roots of subterranean clover and ryegrass is related to changes in the amount of inoculum with distance from the point of inoculation, as well as over time. The rate of spread of the infection front was not constant. Thus it may not be appropriate to calculate mean rates of spread of mycorrhizal fungi over long time periods. [ABSTRACT FROM AUTHOR]

Ryegrass plants were inoculated with Gigaspora margarita, Glomus tenuis or the indigenous mycorrhizal fungi and transplanted into pots containing four New Zealand hill country soils fertilized with finely ground superphosphate or one of five finely ground phosphate rocks. After seven harvests from Dunmore soil and four harvests from three other soils, Peru rock phosphate was the best fertilizer overall (an average of 24% of applied fertilizer phosphate was recovered by plants) followed by superphosphate, Chatham Rise rock, Nauru Is. rock, Christmas Is. rock and Queensland rock (23, 15, 4, 4 and 2% of the phosphate recovered respectively). The fertilizer value of superphosphate decreased rapidly over successive harvests in all soils, with slower decreases in the fertilizer value of Peru and Chatham rock phosphate. The values of Queensland, Nauru Is. and Christmas Is. rock phosphate were very low and largely unaffected by repeated harvesting. Mycorrhizal inoculation greatly influenced phosphate uptake from soil by plants. In 11 out of 28 soil-fertilizer treatments, phosphate uptake by G. tenuis-inoculated plants was increased significantly over plants inoculated with indigenous mycorrhizal fungi. The increased phosphate uptake following inoculation with efficient mycorrhizal fungi tended to decrease over successive harvests, as the available phosphate levels in soil were depleted. [ABSTRACT FROM AUTHOR]

One crop of clover followed by three crops of ryegrass were infected with several mycorrhizal fungi and grown in sterilized soil which had received soluble phosphate or Nauru rock phosphate. Plant growth responses to mycorrhizal infection were larger in later crops. Glomus tenuis was successfully introduced into soil already infested with the indigenous mycorrhizal fungi, and was the most efficient fungus used at stimulating phosphate uptake. In all four crops, Nauru rock phosphate was available to mycorrhizal plants but unavailable to non- mycorrhizal plants. Plants infected with G. tenuis and the indigenous mycorrhizal fungi recovered 10-27% of the phosphate fertilizer applied to the soil while non-mycorrhizal plants recovered only 0.4-13%. [ABSTRACT FROM AUTHOR]

The ability of ryegrass (Lolium perenne L.) to take up and utilize aspartic acid (Asp) and serine (Ser), and the effect of colonization of the roots by the arbuscular mycorrhizal (AM) fungus Glomus fasciculatum (Thax, sensu Gerd.) were studied. The seedlings were grown under controlled condition in a series of micro-lysimeters. All plants were fed with a nutrient solution containing either nitrate, Asp or Ser as the sole N source. After 49 d, they were supplied with 15N labelled nitrate, Asp or Ser for 1 h and harvested. Am colonization increased the growth and total N content of the plants in all cases. Similarly, the amount of Asp or Ser taken up was higher in AM than in control plants. However uptake rates were lower for Ser than for nitrate. Growth of the Asp-fed plants was significantly less than the other two treatments, and uptake of 15N=Asp was lower then uptake of 15N-Ser. Analysis of 15N incorporation into the amino acids extracted from the roots suggests the hydrolysis of Ser followed by re-assimilation of the resulting ammonia via the GS-GOGAT cycle. There were no differences in the patterns of accumulation of amino acids in the root-zone of control and AM-ryegrass. The implication of these results for the pathway of nitrogen transfer between plants is discussed. [ABSTRACT FROM AUTHOR]