Lang Julien, Vigouroux Armelle, El Sahili Abbas, Kwasiborski Anthony, Aumont-Nicaise Magali, Dessaux Yves, Shykoff Jacqui Anne, Moréra Solange, Faure Denis
Institute for Integrative Biology of the Cell (I2BC), CNRS CEA Université Paris-Sud, Université Paris-Saclay, Gif-sur-Yvette, France.
Ecologie Systématique Evolution, CNRS, Université Paris-Sud, AgroParisTech, Université Paris-Saclay, Orsay, France.
ISME J. 2017 Feb;11(2):374-385. doi: 10.1038/ismej.2016.137. Epub 2016 Nov 1.
We investigated the molecular and ecological mechanisms involved in niche expansion, or generalism, versus specialization in sympatric plant pathogens. Nopaline-type and octopine-type Agrobacterium tumefaciens engineer distinct niches in their plant hosts that provide different nutrients: nopaline or octopine, respectively. Previous studies revealed that nopaline-type pathogens may expand their niche to also assimilate octopine in the presence of nopaline, but consequences of this phenomenon on pathogen dynamics in planta were not known. Here, we provided molecular insight into how the transport protein NocT can bind octopine as well as nopaline, contributing to niche expansion. We further showed that despite the ability for niche expansion, nopaline-type pathogens had no competitive advantage over octopine-type pathogens in co-infected plants. We also demonstrated that a single nucleotide polymorphism in the nocR gene was sufficient to allow octopine assimilation by nopaline-type strains even in absence of nopaline. The evolved nocR bacteria had higher fitness than their ancestor in octopine-rich transgenic plants but lower fitness in tumors induced by octopine-type pathogens. Overall, this work elucidates the specialization of A. tumefaciens to particular opine niches and explains why generalists do not always spread despite the advantage associated with broader nutritional niches.
我们研究了同域植物病原体在生态位扩展（即泛化）与特化过程中涉及的分子和生态机制。胭脂碱型和章鱼碱型根癌土壤杆菌在其植物宿主中构建了不同的生态位，分别提供不同的营养物质：胭脂碱或章鱼碱。先前的研究表明，在存在胭脂碱的情况下，胭脂碱型病原体可能会扩展其生态位以同化章鱼碱，但这种现象对植物体内病原体动态的影响尚不清楚。在这里，我们从分子层面深入了解了转运蛋白NocT如何既能结合章鱼碱又能结合胭脂碱，从而促进生态位扩展。我们进一步表明，尽管有生态位扩展的能力，但在共同感染的植物中，胭脂碱型病原体相对于章鱼碱型病原体并没有竞争优势。我们还证明，即使在没有胭脂碱的情况下，nocR基因中的一个单核苷酸多态性也足以使胭脂碱型菌株同化章鱼碱。进化后的nocR细菌在富含章鱼碱的转基因植物中比其祖先具有更高的适应性，但在由章鱼碱型病原体诱导的肿瘤中适应性较低。总体而言，这项工作阐明了根癌土壤杆菌对特定冠瘿碱生态位的特化，并解释了为什么泛化病原体尽管具有更广泛营养生态位相关的优势却并不总是能够传播开来。
