Development of molecular markers linked to quantitative and qualitative assessment of bitterness in lettuce

莴苣（莴苣属）是一种重要的叶菜作物，是大多数沙拉的主要成分。新鲜沙拉的消费量增加，以响应公共卫生运动，吃“5一天”，但增加是小相比，看到水果作物，因为消费者发现蔬菜的味道不如水果的吸引力。生菜种植者和零售商面临的问题之一是，许多消费者不愿意消费生菜，因为他们认为生菜的味道是苦的和不好吃的。导致莴苣苦味的主要成分是类异戊二烯，例如高度浓缩在莴苣中的倍半萜内酯（SL）。这些次级代谢产物是由植物合成的，作为对病原体的防御，SL被认为具有镇痛、止咳和镇静的特性。以前的工作表明，一些SL是共同的两个L。sativa和L. serriola，8-硫酸盐衍生物被鉴定为新的和主要的稳定的SL缀合物，其是多种和组织特异性的。此外，几个不稳定的SL的酸酯被确定，也可能有助于苦的感官品质的莴苣胶乳。最近的代谢组学分析和酶测定确认（狄克逊等人，准备中）乳sativa和L. Serriola已经表明葡萄糖、果糖和蔗糖的水平在驯化的栽培品种中高3-7倍。叶子中糖含量的升高也与甜味有关，因此我们有多个目标来减少生菜叶子的苦味和增加甜味。该项目将使用分子遗传学和代谢相结合的方法来解决以下目标：1确定莴苣基因组中调节SL缀合物和糖生物合成的性状位点。2将分子标记与苦味和甜味性状的QTL进行关联。3鉴定候选基因内的多态性，所述候选基因与可以在作图群体和商业栽培品种中评分的QTL相关并且潜在地支持QTL。4在8-硫酸盐缀合物和糖中定量改变的线中消费者对苦味的感知的评估。5货架期内发生的代谢组学和感官变化的定量。该项目将利用学术和工业合作伙伴的专业知识，并与英国和海外的其他合作伙伴建立合作关系。工业主管是AL Tozer有限公司的植物育种主任，该公司是一家中小型企业，被认为是世界上领先的蔬菜种子育种者之一。AL Tozer有限公司有一个广泛的生菜育种计划，并已生产了80多个品种。该公司寻求开发针对作物苦味等品质性状的育种计划，并利用标记辅助育种的内部专业知识，为这些性状开发分子标记。首席学术主管可以访问生菜RILs（L。sativa x L. serriola），并且之前已经绘制了该种群的质量性状。进一步的人口适合精细映射可与教授戴夫平克在沃里克HRI。这些群体将成为代谢物性状QTL研究的基础。代谢物分析可以在阅读大学的生物中心进行，尽管该项目也能够利用罗森斯特德研究中心的MetRo工作人员（Mike Beale教授和Jane Ward博士）的专业知识，他们进行了L. sativa和L.除了这些物种中的SL特征之外，还可以发现serriola。阅读大学的监督工作将得到丽莎·梅斯文博士的支持，她在食品生物科学公司内经营着一个感官研究小组，在设计和分析感官试验方面具有专业知识。因此，学生将接受一些分子遗传学，生物化学和感官技术的最先进的培训。

Lettuce (Lactuca spp) is an important leafy vegetable crop from the Asteraceae that is the principal component of most salads. Consumption of fresh salads has increased in response to the public health campaign to eat '5-a-day' but the increase is small compared to that seen for fruit crops as consumers find the taste of vegetables less attractive than fruit. One of the problems facing lettuce growers and retailers is that many consumers are reluctant to consume lettuce as they perceive the taste to be bitter and unpalatable. Major components contributing towards the bitter taste of lettuce are isoprenoids such as sesquiterpenoid lactones (SLs) which are highly concentrated within lettuce. These secondary metabolites are synthesised by the plant as a defence against pathogens and the SLs are thought to have analgesic, antitussive and sedative properties. Previous work has shown that a number of SLs are common to both L. sativa and L. serriola, with 8-sulphate derivatives identified as novel and major stable SL conjugates that are variety and tissue specific. Additionally, several unstable SL oxalates were identified that may also contribute to the bitter sensory qualities of Lactuca latex. Recent metabolomics analysis and confirmation by enzyme assays (Dixon et al, in prep.) of L. sativa and L. serriola has shown that the levels of glucose, fructose and sucrose are 3-7 fold higher in the domesticated cultivar. Elevated levels of sugars in the leaf are also linked to a sweet flavour and thus we have multiple targets for reducing bitterness and increasing sweetness of lettuce leaves. The project will use a combined molecular genetic and metabolic approach to address the following aims: 1 Identification of trait loci in the lettuce genome that regulate SL conjugates and sugar biosynthesis. 2 Associate molecular markers with the QTL identified for bitterness and sweetness traits. 3 Identification of polymorphisms within candidate genes that are associated with, and potentially underpin, the QTL which can be scored in the mapping population and commercial cultivars. 4 Assessment of the consumer perception of bitterness in lines that are quantitatively altered in 8-sulfate conjugates and sugars. 5 Quantification of metabolomic and sensory changes that occur during shelf life. The project will draw on the expertise of both the academic and industrial partners, and will establish collaborations with other partners in the UK and overseas. The industrial supervisor is the Director of Plant Breeding at AL Tozer Ltd, an SME regarded as one of the leading breeders of vegetable seeds in the world. AL Tozer Ltd has an extensive lettuce breeding programme and has produced over 80 cultivars. The company seeks to develop a breeding programme targeted at quality traits, such as bitterness, in the crop and to build on in-house expertise in marker assisted breeding to develop molecular markers for these traits. The lead academic supervisor has access to the lettuce RILs (L. sativa x L. serriola) from Prof. Richard Michelmore's lab and has previously mapped quality traits in this population. Further populations suitable for fine mapping are available in collaboration with Prof. Dave Pink at Warwick HRI. The populations will be the basis of QTL studies of metabolite traits. Metabolite analysis can be performed in the BioCentre at the University of Reading, although the project is also able to draw on the expertise of MetRo staff (Prof. Mike Beale and Dr Jane Ward) at Rothamsted Research who performed the initial metabolite analysis of L. sativa and L. serriola in addition to characterising SLs in these species. Supervision at the University of Reading will be supported by Dr Lisa Methven who runs a sensory research group within Food Biosciences and has expertise in designing and analysing sensory trials. Thus the student will receive state-of-the-art training in a number of molecular genetic, biochemical and sensory techniques.