甜高粱茎秆含汁量调控基因JRG的图位克隆与功能分析

Sweet sorghum (Sorghum bicolour) has a juicy and sugar-rich stem, which makes it a remarkable crop for animal feed, paper fibre, liquor brewery and bioethanol. However, the knowledge on the genetic control of stem juice volume is limited. We took advantage of the juice-void trait of Chinese sorghum kaoliang and constructed 12 mapping populations by crossing it with sweet sorghum lines. Initial segregation analysis showed that the trait is controlled by single genetic locus named Juice Retention Gene (JRG), the juice-rich stem being the recessive trait. Our mapping framed the JRG locus into a 350kb region containing 22 candidate genes. The aim of this study is to clone and characterise the JRG gene. For this, we will enlarge the mapping populations to narrow down the mapped region and refine the locus, re-sequence sorghum accessions with rich diversity in stem juice content for association analysis of genome polymorphisms of candidate genes and the juice volume variation, and eventually perform the complementation test using the established sweet sorghum transformation platform. Once the candidate gene(s) cloned and confirmed, a range of molecular and physiological characterisation of the JRG gene and its products will be conducted to dissect its molecular and cellular mode of action. The project is an essential step forward to define important targets for molecular manipulation for sweet sorghum genetic improvement. Fundamentally, the regulation of juice (water) retention in stem/shoot, or the functional role of internal water storage is rarely explored. The outcome of this project will help not only address the long-standing dispute whether the stem juice volume is controlled by single major-effect locus or multiple minor-effect QTLs, but also understand the functional roles of stem/shoot internal water storage in the nutrient and water transportation, the communication between 'source-sink' organs as well as the responses to stresses in a plant.

甜高粱茎杆富含汁液和糖分，我们利用中国地方品种茎秆无汁的特点，同甜高粱品种构建了12个杂交群体，初步分析表明含汁量受单个基因控制，命名为JRG，并将其定位在350kb的区间,包括22个候选基因。本研究旨在克隆JRG基因并系统解析其功能。为此开展三方面的研究：扩大图位克隆群体，缩小定位区间；利用含汁量变异丰富的高粱自然品系资源，开展基因组定向重测序及候选基因序列变异的关联分析，确认候选基因；最后利用遗传转化平台开展基因功能互补克隆JRG基因。将安排相应的分子生物学、生理生化分析阐述其功能。本研究将促进甜高粱定向改良，发挥其青储饲料、造纸纤维、酿酒和生物乙醇产业的作用。同时，茎秆含汁量或器官内部储水的机理与调控鲜有研究。本研究的成果不仅能对学界长期存在的甜高粱含汁量受主效单基因或多个微效QTL控制的争议提供答案，也将帮助诠释作物/植物茎秆储水在水分与养分转运、"源-库"信号交换方面的作用。

茎秆水分的储存和运输是保证陆生植物正常生长发育的重要前提。维管组织的进化和产生在茎秆水分储存转运方面，具有革命性的意义。深入解析茎秆水分的储存和运输的作用机理和调控网络，为作物的遗传改良提供重要的理论基础。高粱分为普通籽实高粱（Grain sorghum）与甜高粱（Sweet sorghum），二者显著的差异之一是籽实高粱秸秆通常汁液含量低，而甜高粱茎秆则富含水分。我们开展分子遗传学与基因组学研究，克隆与鉴定高粱秸秆水分（汁液）的调控基因Dry，发现该基因通过调节木质部和次生细胞壁的细胞分化和发育，影响茎秆水分储运能力，遗传进化发现Dry基因在有汁高粱中受到正选择，有汁亚群和无汁亚群的多态性具有明显差异，而无汁栽培高粱和野生高粱中多态性没有明显差异，说明Dry在甜高粱进化过程受到正向选择，是一个重要的甜高粱起源与进化的关键基因。