Elucidation of origin of citrus based on information from chromosome analysis

柑桔属芸香科（Rutaceae）七亚科之一的枳壳亚科（Aurantioideae），是世界上最重要的水果作物之一，但其起源及各亚科种间的亲缘关系一直不清楚。染色体数目分析表明，几乎所有的枳壳亚科植物都具有二倍体（2n=2x=18）染色体。只有两个种是四倍体（2n=4x=36）。五叶小橘（Glycosmispentaphylla）是一种二倍体和六倍体（2n=6x=54）的混倍体，采用色霉素A3（CMA）荧光染色法，对枳壳亚科16属21种植物的染色体CMA带型进行了研究和比较。根据CMA阳性带的数目和位置将这些染色体分为六种类型：A：2条端粒带和1条近端带，B：1条端粒带和1条近端带，C：2条端粒带B ...更多信息 ands，D：一条端粒带，E：无带，Dst：具有随体染色体的D型。每个种都具有1 ~ 4种染色体类型和独特的CMA带型。各族和亚族中的高级属如Merrillia和Feroniella均显示异染色质（CMA阳性带）。染色体构型丰富。Swinglea sporsosa是一个不含异染色质的染色体组，被认为是最原始的染色体构型，是研究Citrus族进化的关键属，利用核糖体RNA基因（rDNA）进行荧光原位杂交（FISH）是研究Citrus族染色体组发生的有力工具。因此，对从原始到高级的七个属进行了5S rDNA的荧光原位杂交。在7个属中的6个属中检测到2个5SrDNA位点。枳属有6个5SrDNA位点。从这些结果来看，2可能是枳壳亚科的5SrDNA位点的一个碱基数。5SrDNA位点数的多样性发生在真柑橘树分化后。少

Although citrus, belong to Aurantioideae which is one of the seven subfamilies of Rutaceae, is the one of the most important fruit crop in the world, its origin and phylogenic relationships among species in Aurantioideae has been unclarified. Therefore in this study, we conducted chromosome analysis to elucidate the phylogenic relationships and evolution within Aurantioideae.The chromosome number analysis revealed that almost all Aurantioideae species had diploid (2n=2x=18) chromosomes. Only two species were tetraploid (2n=4x=36). Glycosmis pentaphylla was a mixoploid having diploid and hexaploid (2n=6x=54) cells.Fluorochrome staining with chromomycin A3 (CMA) was used to characterize and compare the CMA banding patterns of chromosomes of 21 species from 16 genera of Aurantioideae. These chromosomes were classified into six types based on the number and position of CMA-positive bands ; A : two telomeric and one proximal band, B : one telomeric and one proximal band, C : two telomeric b … More ands, D : one telomeric band, E : without bands, and Dst : type D with a satellite chromosome. Each species possessed one to four types of chromosomes and unique CMA banding patterns. The advanced genera in each tribe and subtribe such as Merrillia and Feroniella showed heterochromatin (CMA-positive bands). rich chromosome configuration in general. Swinglea glutinosa without heterochromatin rich chromosome, which is considered to be the most primitive chromosome configuration, seems to be the key genus for clarifying the evolution of the tribe Citreae.Fluorescent in situ hybridization (FISH) using ribosomal RNA genes (rDNA) is a powerful tool for phylogenic studies. Thus FISH of 5S rDNA was carried out in seven genera from primitive to advanced one. Two 5S rDNA sites were detected in six out of seven genera. Poncirus had six 5S rDNA sites. From these results, two seem to be a base number of 5S rDNA sites in Aurantioideae. Diversity of number of 5S rDNA sites occurred after the true citrus fruit trees were differentiated. Less