The regulation of arbuscular mycorrhizal symbiosis by phosphate in pea involves early and systemic signalling events

Most plants form root symbioses with arbuscular mycorrhizal (AM) fungi, which provide them with phosphate and other nutrients. High soil phosphate levels are known to affect AM symbiosis negatively, but the underlying mechanisms are not understood. This report describes experimental conditions which triggered a novel mycorrhizal phenotype under high phosphate supply: the interaction between pea and two different AM fungi was almost completely abolished at a very early stage, prior to the formation of hyphopodia. As demonstrated by split-root experiments, down-regulation of AM symbiosis occurred at least partly in response to plant-derived signals. Early signalling events were examined with a focus on strigolactones, compounds which stimulate pre-symbiotic fungal growth and metabolism. Strigolactones were also recently identified as novel plant hormones contributing to the control of shoot branching. Root exudates of plants grown under high phosphate lost their ability to stimulate AM fungi and lacked strigolactones. In addition, a systemic down-regulation of strigolactone release by high phosphate supply was demonstrated using split-root systems. Nevertheless, supplementation with exogenous strigolactones failed to restore root colonization under high phosphate. This observation does not exclude a contribution of strigolactones to the regulation of AM symbiosis by phosphate, but indicates that they are not the only factor involved. Together, the results suggest the existence of additional early signals that may control the differentiation of hyphopodia

International genome-wide meta-analysis identifies new primary biliary cirrhosis risk loci and targetable pathogenic pathways.

Primary biliary cirrhosis (PBC) is a classical autoimmune liver disease for which effective immunomodulatory therapy is lacking. Here we perform meta-analyses of discovery data sets from genome-wide association studies of European subjects (n=2,764 cases and 10,475 controls) followed by validation genotyping in an independent cohort (n=3,716 cases and 4,261 controls). We discover and validate six previously unknown risk loci for PBC (Pcombined<5 × 10(-8)) and used pathway analysis to identify JAK-STAT/IL12/IL27 signalling and cytokine-cytokine pathways, for which relevant therapies exist

SEASONAL PATTERNS OF HOST GROWTH, FUNGAL MORPHOLOGY, AND ROOT CARBOHYDRATE AND PHOSPHORUS CONTENT IN A GREEN ASH MYCORRHIZA

Two long-term experiments with vesicular-arbuscular {VA} mycorrhizal green ash seedlings (Fraxinus pennsylvanica Marsh.) were conducted to determine seasonal changes in mycorrhizal morphology, spore production, host plant growth, and root carbohydrate and phosphorus levels. Seedlings, with or without the VA mycorrhizal fungus Glomus macrocarpum var. macrocarpum Tul. & Tul., were grown in a greenhouse under natural photoperiods and low and high nutrient regimes. The seedlings were moved to a lathhouse to overwinter and were returned to the greenhouse in the spring. Inoculation with G. macrocarpum significantly increased the growth and P content of green ash seedlings receiving a low nutrient addition over similarly treated noninoculated seedlings. At the end of their first growing season, mycorrhizal plants were 25cm tall, weighed 4.2g, and contained 50 nmoles P mg(\u27-1) root. The non-mycorrhizal plants were 14.5cm tall, weighed 0.9g, and contained 25 nmoles P mg(\u27-1) root. Non-mycorrhizal seedlings receiving a high nutrient solution at frequent intervals grew as well and contained similar amounts of P as mycorrhizal seedlings. Concentration of nutrient solution had little effect on the growth of mycorrhizal seedlings. Content of soluble sugars and starch in roots of green ash followed predictable seasonal and phenological patterns, but showed little clear, consistent trend with respect to mycorrhizal or nutrient treatments. Patterns of growth and development of the host and morphology of the VA fungus in the first growing season suggest a yearly cycle with three phases. Phase I (late spring) is a period of fast shoot growth, slow root growth, rapid colonization of the root system by the fungus, and greater numbers of fungal arbuscules than vesicles. Phase II (summer) is a period of fast root growth and decline in percentage root length infected. Phase III (late summer and fall) is characterized by senescing leaves, infection percentages increasing to a static level, greater numbers of fungal vesicles than arbuscules, and increased numbers of mycorrhizal spores in the rhizosphere. This cycle continued in the second growing season except that the percentage root length infected by the fungus remained fairly constant

Organic and Conventional Farming Systems: Environmental and Economic Issues.

Heavy agricultural reliance on synthetic-chemical fertilizers and pesticides is having serious impacts on public health and the environment. The estimated environmental and health care costs of the recommended use of pesticides in the U.S. are about $10 billion per year (Pimentel 2005). In the United States over 90 % of corn farmer

Increased Sporulation of Vesicular-Arbuscular Mycorrhizal Fungi by Manipulation of Nutrient Regimens

Adjustment of pot culture nutrient solutions increased root colonization and sporulation of vesicular-arbuscular mycorrhizal (VAM) fungi. Paspalum notatum Flugge and VAM fungi were grown in a sandy soil low in N and available P. Hoagland nutrient solution without P enhanced sporulation in soil and root colonization of Acaulospora longula, Scutellospora heterogama, Gigaspora margarita, and a wide range of other VAM fungi over levels produced by a tap water control or nutrient solutions containing P. However, Glomus intraradices produced significantly more spores in plant roots in the tap water control treatment. The effect of the nutrient solutions was not due solely to N nutrition, because the addition of NH(4)NO(3) decreased both colonization and sporulation by G. margarita relative to levels produced by Hoagland solution without P