高粱属分子系统学及栽培高粱和约翰逊草基因组起源的研究

Natural hybridization and polyploidization are important modes of plant speciation and evolution. About 2/3 of grass species (Poaceae) are estimated to have arisen as a result of polyploidization events, the polyploid origin researches of few cereal crops have made progress at the molecular level to date, while the conclusion from one research system can't be extented to the related groups. In the project, the representative species of Sorghum group and all species of Sorghum Moench will be investigated to explore the interspecific phylogeny of Sorghum and the genome origins of cultivated sorghum [S. bicolor (L.) Moench] and Johnsongrass [S. halepense (L.) Pers.] in the phylogenetic and cytogenetical contexts. The project aims to: (1) reconstruct phylogeny of Sorghum based on six low copy nuclear gene and six chloroplastid gene sequences, identify the sister lineages to cultivated sorghum and Johnsongrass; (2) identify the genome constitutions and the distribution of homoeologous repeat sequences of related species on the metaphase chromosomes of cultivated sorghum and Johnsongrass by genomic in situ hybridization (GISH) method, design probes based on the biparental inheritance phylogeny and maternal inheritance phylogeny of Sorghum, and develope genome origin hypotheses for cultivated sorghum and Johnsongrass, respectively; and (3) estimate the origin time of northeast African sorghum by employing the molecular clock method, reveal the influence of paleoclimatic changes on genealogy differentiation of Sorghum. The research objective is to address the complex interspecific phylogeny of Sorghum and enhance our understanding of the exact genome donors for cultivated sorghum and Johnsongrass at the gene and genome repeat sequence levels. The highly integrative findings will update the traditional recognitions of polyploid origins in Sorghum.

自然杂交和多倍化是植物物种形成和演化的重要途径。自然界大约2/3禾本科植物属于多倍体，仅少数谷类作物的多倍体起源研究在分子水平取得进展,个别体系得到的结论不能推广到相关类群。本项目针对禾本科高粱属群代表种和高粱属全部物种，结合分子系统学和细胞遗传学证据，开展如下研究：(1)筛选六个低拷贝核基因和六个叶绿体基因序列，重建高粱属谱系发育关系，鉴别栽培高粱和约翰逊草姐妹谱系；(2)采用基因组原位杂交方法，根据双亲遗传和母系遗传系统发育树设计探针，鉴定栽培高粱和约翰逊草基因组组成，研究近缘物种同源重复序列的空间分布，提出栽培高粱和约翰逊草的基因组起源假说；(3)采用分子钟方法，估测非洲东北部栽培高粱的起源时间，揭示古气候变迁对高粱属谱系分化的影响。本研究将在基因和基因组重复序列水平，解决高粱属复杂的种间关系，深化理解栽培高粱和约翰逊草独特的亲本来源。研究结果将更新高粱属多倍体起源的传统认识。

我们针对禾本科高粱属群代表种和高粱属全部物种，开展分子系统学和细胞遗传学研究。低拷贝核基因系统发育研究显示高粱属的分子系统学范畴扩大，高粱属包括3个遗传谱系(即高粱谱系、多毛高粱-异高粱谱系、有柄高粱谱系)，我们将有柄小穗完全退化的单型属(Cleistachne Benth.)转隶至高粱属内—Sorghum sorghoides (Benth.) Q. Liu & P.M. Peterson，首次发现四倍体物种S. sorghoides杂交起源的核基因证据。采用双色GISH方法研究栽培高粱和约翰逊草与近缘物种基因组关系，发现栽培高粱与近缘物种基因组分化程度依次为：S. bicolor-S. × drummondii<S. bicolor-S. × almum<S. bicolor-S. arundinaceum<S. bicolor-S. propinquum，其中栽培高粱与S. × almum及S. × drummondii基因组分化程度较小，暗示这两个物种相对年轻，S. arundinaceum探针呈点状或带状杂交信号，支持栽培高粱在相对古老时间起源于S. arundinaceum，约翰逊草与近缘物种基因组分化程度依次为：S. halepense-S. bicolor<S. halepense-S. arundinaceum<S. halepense–S. propinquum，推测三者可能是石茅基因组供体。采用分子钟方法估测高粱属谱系分化大约发生在12.7百万年前，推测中新世中期至上新世时期，东非裂谷持续隆升产生的片段化生境促进高粱属在热带东非分化。本项目研究结果更新高粱属多倍体起源的传统认识，研究结果为谷类作物多倍体基因组起源研究提供理论参考。