Linkage between plant sugar and fungal phosphate ex-port in ectomycorrhizal symbiosis

植物根和某些土壤真菌之间的紧密结合形成了一个新的器官--外生菌根，这对北方和温带森林生态系统的成功至关重要。外生菌根共生的一个主要功能是真菌和植物之间营养物质(如磷酸盐)和碳水化合物的双向交换。然而，众所周知，优质的植物营养可以抑制外生菌根的形成。另一方面，某些真菌似乎在每“单位营养”中获得不同数量的碳水化合物。然而，除了互惠作用外，人们对调节磷酸盐和碳水化合物交换的分子机制知之甚少。虽然还没有真菌磷输出载体的特征，但最近发现了植物糖外排载体。由于这个甜味基因家族中的某些成员是以依赖于外生菌根的方式诱导的，它们将在这一应用中用于解决相互作用的磷酸盐和碳水化合物交换的分子机制。一个目标将是发现允许共生特异性基因调控的启动子元件和转录因子。此外，a)糖出口有缺陷或b)与真菌菌丝竞争葡萄糖吸收的转基因植物将被用来研究碳和磷营养之间的联系。在这里，将进行时间分辨的P/C成像和测定调制植物的菌根中的碳水化合物和磷酸盐通量。在杨树中观察到的机制是否可以推广，将在云杉外生菌根中进行研究。将鉴定甜味同系物，并将研究在单株树木和一些不同的外生菌根真菌之间形成的菌根对基因表达的诱导强度。结合相关真菌配对的测定，这将允许比较不同真菌种类对甜味诱导的影响。由于这种分析将对生长在不同磷素有效性土壤中的树木进行，这种方法将有助于将C/P比的变化与甜味基因诱导联系起来。因此，本实验将回答甜味基因表达的诱导强度是否可以作为外生菌根真菌碳水化合物支持的关键特征的问题。这将(在未来的研究中)允许快速检查不同外生菌根真菌在自然条件下的生态特性。

The tight association between plant roots and certain soil fungi forming a novel organ, the ectomycorrhiza, is essential for the success of boreal and temperate forest ecosystems. A major function of ectomycorrhizal symbiosis is the bidirectional exchange of nutrients (e.g. phosphate) and carbohydrates between fungi and plants. However, superior plant nutrition is known to inhibit ectomycorrhiza formation. On the other hand, certain fungi seem to gain different amounts of carbohydrates per "unit of nutrients" delivered to the plant. Nevertheless, apart from mutualism, little is known about the molecular mechanisms regulating phosphate and carbohydrate interchange. While no fungal phosphate exporter have yet been characterized, plant sugar efflux carrier have been recently discovered. As certain member of this SWEET called gene family are induced in an ectomycorrhiza-dependent manner they will be used in this application to address molecular mechanisms of mutualistic phosphate and carbohydrate exchange. One target will be the discovery of promoter elements and transcription factors that allow a symbiosis specific gene regulation. Furthermore, transgenic plants that are a) defective in sugar export or b) compete with fungal hyphae for glucose uptake will be used to investigate the link between carbon and phosphate nutrition. Here, time resolved P/C imaging and determination of carbohydrate and phosphate fluxes in mycorrhizas of modulated plants will be performed. Whether the observed mechanism in poplar can be generalized will be investigated in Picea abies ectomycorrhizas. SWEET homologs will be identified and mycorrhizas formed between single trees and a number of different ectomycorrhizal fungi will be investigated for induction strength of gene expression. In combination with determination of the associated fungal partner this will allow a comparison of the impact of different fungal species on SWEET induction. As this analysis will be performed for trees grown in soils with different phosphate availability, this approach will help to link the variance of C/P ratios to SWEET gene induction. This experiment will therefore answer the question whether the induction strength of SWEET gene expression can be a key feature ectomycorrhizal fungal carbohydrate support. This would (in future research) allow a quick inspection of the ecological properties of different ectomycorrhizal fungi under natural conditions.