Phylogenetic Relationships Of Avena Species Based On Nuclear Rpb2 Gene And Genetic Diversity In Chinese Naked Oats By Using Genotyping By Sequencing

The genus Avena belongs to the grass family(Poaceae),is composed of approximate 30 species with the basic chromosome number of seven.There are four main genome groups,A,B,C and D,which form all the Avena species in three ploidy levels.Since many Avena species are similar morphologically and overlapping in geographic distribution,it is difficult to identify them with gross-morphological characters.In addition,the high homologies among the Avena genomes constrained the progress of unraveling the relationships of Avena species.In particular,due to the absence of the diploids with the B and D genome,the genome donor of the B and D genome in polyploids becomes the most complicated problem in genus Avena.Cultivated hexaploid oat(referred to as oat)is one of the most important cereal crops in the world and occupies an important role in our agricultural system.Oat is generally divided into naked oat and covered oat.Compared with covered oat,naked oat is higher in nutritional value but inferior in yield,therefore,breeding new naked varieties with high yield is the key to the development of naked oat.It has been widely acknowledged that genetic diversity plays an important role in crop improvement since it provides opportunities for breeders to develop new cultivars with desirable traits.China is the origin center of naked oat,and keeps the largest collection of naked oat germplasm,However,there are few studies have been reported on the genetic diversity of naked oat.In this study,we utilized cloning technology to obtain the sequences of oat nuclear gene Rpb2,and to investigate the relationships among Avena species.And we also used GBS to sequence a naked oat collection from 12 provinces of China to investigate their genetic diversity and population structure.The remain results are summarized as follows:1.The Rpb2 sequences from A genome diploids were aligned and carried out the phylogenetic analysis.The NJ three showed that the diploids with the same genomic constitution had the tendency to cluster together.The As genome diploids were more diverse than other A genome diploids.We combined all Rpb2 sequences from the A genome diploids with the AB genome tetraploids to construct a NJ phylogenetic tree.The results revealed the structure differences between the AB genome tetraploid species A.agadiriana with the other three AB genome tetraploids,and indicated the allotetraploid origin of the AB genome tetraploids.The As genome diploids might be the A genome donor of the AB genome tetraploids A.barbata?A.abyssinica and A.vaviloviana,while the B genome donor of these AB genome tetraploids need to further study.The genome donor for A.agadiriana might be the As genome diploid A.lusitanica and(or)A1 genome diploid A.longiglumis.2.Phylogenetic analysis by combining the Rpb2 sequences from the A and C genome diploids with sequences from the AC genome tetraploids showed AC genome tetraploids A.murphyi is closer to A.insularis than A.maroccana,and indicated that the Ac genome diploid A.canriensis and As genome diploid A.hirtula might be served as the genome donor of A.murphyi and A.insularis.The genome donor of A.maroccana might be the As genome diploids.Both types of C genome diploids showed close relationship with the AC genome tetraploids.3.The Rpb2 sequences obtain from the hexaploid species were divided into three groups,part of them were clustered with Rpb2 sequences from the C genome diploids,therefore referred to as the C genome,some of them fell into the cluster including the As genome diploids,hence referred to as the A genome,while the remaining clustered with the Ac genome diploid A.canariensis and the As genome diploid A.hirtula and the AC genome tetraploid species A.insularis.Considering the genomic constitution of the hexaploid species,this cluster might represent the D genome,if that is true,the D genome donor of the hexaploid might be Ac genome diploid A.canariensis and(or)As genome diploid A.hirtula,and the genome consistution of the AC genome tetraploid species A.insularis should be the CD genome.4.In this study,we sequenced a core collection of naked oat germplasm from 12 provinces of China by using GBS.The results revealed that the oat lines from Shianxi,Inner Mongolia,Hebei and Sichuan have higher genetic diversity that those oat lines from other provinces.5.PCA results showed the first five PCs can explain 55.3%of the variation,of which the first PC explain 33.7%,this indicated strong population structure existed in naked oats.STRUCTRE analysis divided most naked oat germplasm into two subpopulations.