Phylogeography Study Of Siraitia Grosvenorii

Siraitia grosvenorii is an important economic species peculiar to southern China.It has long been widely used as food and beverage raw materials and traditional Chinese medicine.Its fruit contains non-caloric sweetener mogroside,which are about 300 times sweeter than sucrose,and can be used as sucrose substitutes for diabetics and obese patients.S.grosvenorii has been cultivated in Guilin,Guangxi,China for more than 200years.Wild S.grosvenorii is widely distributed in subtropics forests and mountain valleys in China.A total of 130 samples,13 wild S.grosvenorii populations distributed in Guangxi,Guangdong,Hunan and Jiangxi were collected in this study.In addition,21samples of 12 cultivated varieties from Yongfu,Lingui and Longsheng County in Guangxi were collected.In this paper,the phylogenetic distribution pattern,genetic diversity,genetic structure and evolutionary history of S.grosvenorii population and the origin center of cultivated S.grosvenorii species were discussed by molecular markers of three spacer sequence fragments?trnR-atpA,trnH-psbA and trnL-trnF?and two single copy nuclear genes?CHS,EDL2?of S.grosvenorii.The results showed that:1)S.grosvenorii had high genetic diversity?cpDNA,h=0.735,n=6;CHS,h=0.914,n=45;EDL2,h=0.834,n=15?.Chloroplast markers showed high genetic differentiation among wild S.grosvenorii populations(G_ST=0.922).Based on the clear haplotype network map and haplotype geographic distribution map of chloroplasts and the division of flora hotspots,we speculate that S.grosvenorii may have four refuge during the Quaternary glacial period,namely,the western part of the Nanling Mountains,that is,the northeastern part of Guangxi.?MES,SJ,BL,JT and JX populations?defined by Yuechengling in the west of Nanling Mountain and Dayao Mountain in Jinxiu,Represented by haplotypes C1 and C4 of cpDNA.Mengzhuling Mountain?DX,HZ and ZQ populations?in the middle of Nanling Mountain,the haplotype C2 is concentrated in this assumed refuge.Dayu Mountain and Wugong Mountain in the east of Nanling Mountain?SG,JLS,RY and WGS populations?,represented by haplotypes C3 and C6.and Yunkai Mountain?PB populations?,represented by haplotype C5.2)The haplotype network map and geographic distribution map of nuclear genes show a homogeneous distribution model.We speculate that this is due to the limited expansion of S.grosvenorii population during the ice age and the transmission of nuclear genes through pollen as important factors for the secondary contact between populations in post-glacial refuges.3)Based on chloroplast DNA and nuclear DNA data,haplotype variation?H_S?of all wild S.grosvenorii populations were?cpDNA,H_S=0.062;CHS,H_S=0.559;EDL2,H_S=0.589?.Permut test showed that neither cpDNA nor nuclear DNA had pedigree geographic structure.Consistent with haplotype distribution,SAMOVA analysis of cpDNA and nDNA showed that K value increased from 2 to 12,and F_CTT continued to increase with the increase of K value.Therefore,SAMOVA failed to reveal any meaningful geographical population grouping.Mantel test results showed that the correlation between genetic distance and geographic distance between cpDNA and nuclear DNA population was not significant?P>0.05?,indicating rejection of variation caused by distance isolation.4)The chloroplast DNA and nuclear DNA?CHS?markers indicate that MES,BL,JX,JT and SJ population in northeastern Guangxi are the origin centers of cultivated S.grosvenorii varieties in Guilin,Guangxi.We compared the diversity of S.grosvenorii population between cultivated S.grosvenorii and its origin.It was found that the diversity of S.grosvenorii population from the northeast of Guangxi was higher than that of cultivated S.grosvenorii.Nuclear gene data show that Nanling region has high genetic diversity.Therefore,this region should be considered as the diversity protection center of S.grosvenorii and another treasure trove for future development of S.grosvenorii germplasm resources.We observed that most of the variation was distributed in the population.?CHS,50.95%;EDL2,37.86%?.Therefore,germplasm collection should be sampled from a wide range of geographic origins.We observed that most of the variation was distributed within the population?EDL2,62.14%;CHS,49.05%?,which is indicative of the collection of more individuals within the population.5)In addition,we further sequenced and assembled the complete chloroplast genome sequence of S.grosvenorii.In this study,Illumina sequencing method was used to establish its complete chloroplast?cp?genome.The complete cp genome is 157,132bp in length,with a large single copy region?LSC?of 92,442bp and a small single copy region?SSC?of 21,232 bp,which were separated by a pair of inverted repeats?IR?regions of21,729 bp.The complete cp genome consists of 85 coding sequences?CDS?,39 tRNA and 8 rRNA genes.and the maximum likelihood?ML?phylogenetic tree of 20 complete chloroplast genomes of S.grosvenorii and related species,which roughly knows the phylogenetic position of S.grosvenorii in Cucurbitaceae.The complete chloroplast genome sequence information reported here will provide important genetic information for the protection of S.grosvenorii germplasm resources in the future.