"Adaptation of Frankia, alders, and their symbiosis to environmental stress. Adaptation au stress environnemental de Frankia, des aulnes et de leur symbiose."

法兰克属丝状放线菌普遍存在，并在全球固氮中发挥着重要作用。它们与寄主植物（放线根植物，其中包括桤木）建立了类似于豆科植物与根瘤菌的根瘤共生关系。在北美，桤木因其分布、健壮性和对各种恶劣环境条件的适应性而受到特别关注。尽管放线根桤木通常用于荒地的植被恢复，但很少有研究关注自然和人为胁迫（土壤养分缺乏、重金属）如何影响桤木放线根根系共生。考虑到franfranae在其腐生生命周期中直接暴露于这些压力，这些问题就更加重要了。具体来说，我将研究：1-生长中的法兰克属群体的细胞分化（即大量转化为异型菌丝），2-桤木，法兰克属和外生菌根共生体在金属污染土壤中的相互作用研究，3-根瘤中的细菌群体。我的研究项目主要集中在阐明放射线桤木和法兰克属植物如何适应环境压力（包括自然和人为）。通过这些知识，我们能够了解人类活动对这些在加拿大无处不在的生物的影响，并根据桤木物种和法兰克菌株组合的自然潜力定制根降解或植物提取技术。必须强调的是，对法兰克菌共生（放线根菌共生）的研究相对不足。这与它们在自然界中的重要性形成鲜明对比；据估计，全球固氮的15%至25%可归因于这些生物。不幸的是，对frankiae及其共生关系的研究存在许多技术上的困难。我正在用最先进的技术，以系统的方式解决这些困难，并以综合的方式进行这项重要的研究。其结果是培养了高素质的学生，并使工业合作伙伴参与其中，造福科学和社会。

Filamentous actinobacteria of the genus Frankia are ubiquitous and participate significantly in global nitrogen fixation. With their host plants (actinorhizal plants, amongst which alders), they establish a root nodule symbiosis analogous to that of legumes with rhizobia. In North America, alders are of particular interest for their distribution, robustness and adaptation to a wide range of harsh environmental conditions. Although actinorhizal alders are routinely used for the revegetation of derelict lands, little research has focussed on how natural and anthropogenic stress (soil nutrient deficiency, heavy metals) affect the alder actinorhizal symbiosis. These questions are even more important considering that frankiae, in their saprophytic life cycle, are directly exposed to these stresses. Specifically, I will study: 1- cellular differentiation of growing Frankia spp. populations (i.e. massive conversion to difformed hyphae), 2- the study of interactions between alder, frankiae and ectomycorrhizal symbionts in soils that are contaminated with metals, and 3- the bacterial populations in root nodules. My research program focusses mainly on elucidating how actinorhizal alders and Frankia sp. adapt to environmental stress (both natural and anthropogenic). Through this knowledge, we are able to understand the impact of human activity on these organisms which are ubiquitous in Canada, and tailor rhizodegradation or phytoextraction technologies according to the natural potential of combinations of alder species and Frankia strains. It must be emphasized that the Frankia symbiosis (actinorhizal symbiosis) is relatively understudied. This contrasts with their importance in Nature; it is estimated that 15% to 25% of global nitrogen fixation can be attributed to these organisms. Unfortunately, the study of frankiae and their symbiosis to comprise a number of technical difficulties. I am addressing these difficulties using state-of-the-art techniques, in a systematic fashion, and pursuing this important research in an integrated manner. This results in the training of highly competent students, and in the involvement of industrial partners for the benefit of science and society.