Decoding the chitin signatures generated by Xylella fastidiosa

降解甲壳素的能力对于真菌和细菌病原体的生存和定植成功至关重要，其中许多病原体是重要农学疾病的病原体。对于缺乏甲壳素的细菌病原体来说，如果通过昆虫传播，甲壳素的降解在对抗寄主定植真菌和在其媒介中生存方面发挥了主要作用。在欧洲的“优先有害生物名单”中列出的病原体之一是顶端木霉。这种昆虫传播的细菌是橄榄快速衰退综合症(OQDS)的原因，对过去十年的疫情非常重要。从缺乏疾病控制的角度来看，了解尖端X线虫如何定植宿主的迫切性是显而易见的。以前有报道说，几丁质酶CHIA是由几丁质菌分泌的，i)利用几丁质作为碳源，可能来自其昆虫载体和木质部真菌，ii)促进昆虫媒介的传播，iii)植物系统感染所必需的，可能是反对植物定植真菌。我们的关注点是CHIA，因为这种细菌几丁质酶在其模拟的3D结构中携带一个不寻常的环，可以决定底物特异性，并且v)可能释放几丁质低聚体，可以调节X.Fastidiosa宿主的免疫反应。尽管对几丁质酶的研究已经有几十年了，但我们对底物-结构-产物-生物活性的关系知之甚少，这些关系是理解其作为毒力因子的作用的关键。在这里，我们的目标是回答两个关键问题：1.顶端X菌是如何降解甲壳素的？使用一系列定义的甲壳素底物和不同的生物来源分析CHIA的活性和特异性将揭示降解产物，然后进行生物活性分析。结构-功能关系将在硅胶、体外和体内进行探索。2.由尖吻假单胞菌产生的甲壳素低聚体的免疫调节潜力是什么？比较模型宿主和作物宿主对CHIA产物的不同免疫反应，以及评估模式识别受体介导的免疫，可能会为这个问题提供见解。作为一个重要的毒力因子，我们的总体目标是更好地了解Chia功能的分子细节，并阐明其在植物系统性侵染中的作用。我们设想，这些知识可能对生物技术用途有用。

The ability to degrade chitin is essential for the survival and colonization success of fungal and bacterial pathogens, many of which are causal agents of agronomically-important diseases. For bacterial pathogens, which lack chitin, the degradation of chitin plays a major role in opposing host-colonizing fungi and surviving in its vector, if transmitted by insects. One of the pathogens ranked in the “list of priority pests” for Europe is Xylella fastidiosa. This insect-transmitted bacterium is the cause of the OLIVE QUICK DECLINE SYNDROME (OQDS) and important for outbreaks over the past ten years. The urgency to develop an understanding how X. fastidiosa colonizes its hosts is apparent from the lack of disease control. Previously it has been reported that a proposed chitinase, chiA, is secreted by X. fastidiosa and i) confers utilization of chitin as a carbon source, potentially from its insect vectors and xylem-colonizing fungi, ii) promotes transmission by insect vectors, and iii) is required for systemic infection in plants, maybe opposing plant-colonizing fungi. Our focus is chiA, because this bacterial chitinase iv) carries an unusual loop in its modelled 3D structure that could determine substrate specificity, and v) likely releases chitin oligomers that could modulate immune responses in hosts of X. fastidiosa. Although chitinases have been studied since decades, we have little knowledge on substrate-structure-product-bioactivity relationships, which are key to understanding its role as virulence factors. Here, our goal is to answer two key questions: 1. How does X. fastidiosa degrade chitin? Profiling chiA activity and specificity using a series of defined chitin substrates and different organismal sources will reveal degradation products then subjected to bioactivity analysis. Structure-function relationships will be explored in silico, in vitro and in vivo. 2. What is the immunomodulatory potential of chitin oligomers produced by X. fastidiosa? Comparing different immune responses to chiA products in model and crop hosts, together with assessing pattern recognition receptor-mediated immunity are likely to provide insights into this question. Being an important virulence factor, our overall aim is to better understand the molecular details of chiA function and clarify its role in systemic plant infection. We envisage that this knowledge could be useful for biotechnological purposes.