Chromosomal Characterization In Fortunella Hindsii And Expression Analysis Of RDNA In Citrus Somatic Hybrids

Fortunella hindsii,which originated from China,is one of the most important materials in citrus plants study.With the characteristics of small plant size,which is convenient for observation in lab;short juvenile,which can blossom within one year after seed germination;existing of poly and mono embryo materials in different regions.Based on the above botanical characteristics,it is possible to become a model citrus plant.Cytogenetical analysis is necessary in understanding the genetic background of model plant,while little cytogenetic study has been done in F.hindsii.So chromosomal karyotype analysis,Chromomycin A3(CMA)banding observation,45 S rDNA FISH,Genome in situ hybridization(GISH)and hierarchical cluster analysis based on CMA banding types were conducted in our research.At the same time,the expression of rDNA in three somatic hybrids were analyzed.Results were showed as below:1.All of these four Fortunella and two Poncirus accesions presented 18 chromosomes after stained by CMA/DAPI double staining,while their CMA banding types showed big variety,like 2A+2C+12D+2G in JG;1A+3B+1C+11D+1E+1G in PE1;2B+2C+12D+2E in PE2;4B+2C+10D+2E in ME1;4B+7D+7F in ZK;3B+9D+6F in ZSZ.2.Results of 45 S rDNA FISH showed that six 45 S rDNA sites were found both in polyembryo PE1 and monoembryo ME1.In PE1 four of these signals were located in near centromere of one A type and three B type chromosomes,another two signals were located in the terminal of one C type and one D type chromosome.In ME1 four of these signals were located in near centromere of four B type chromosomes,another two signals were located in two C type chromosomes.While there were five 45 S rDNA sites in ZK and ZSZ.In ZK,four signals were located in near centromere of four B type chromosomes and another one signal were located in the terminal of one D type chromosome.In ZSZ,three signals were located in near centromere of three B type and another two signals located in the terminal of two D type chromosomes.3.Tel-45 S rDNA two color FISH showed all the telomere signals lie in the end of 18 chromosomes,two 45 S rDNA sites were close to telomere signals,while another four 45 S rDNA sites located near centromere.4.GISH results showed that about 12 chromosomes with hybridization signals,which most of them were co-localized with CMA banding.5.Hierarchical clustering analysis based on CMA banding types of forty citrus accessions showed a close relationship between F.hindsii and Citrus genus plants.6.rDNA expression analysis in three citrus somatic hybrid and their parents showed that rDNA from two parents were expressed in BG,HR and PR..From these results,we had a preliminary understanding about the phylogenetic role of F.hindsii in Citrus family.Remarkably,one of the mono embryo materials ME1 is homozygous,it has the potential to become a model citrus plant in theory.