Analysis On Genetic Variation And DNA Methylation Of Different Loquat Ploidies

The polyploidy phenomenon play a significant function in higher plant evolution. After polyploidization plant will derived a large number of repeat sequences, which are favorable resources of gene selection, evolution and mutation, and numerous sequences loss and insertion also provide more choices for plant evolution. The reason for widespread polyploidy is that polyploid species compared to its diploid ancestors have a wider range of adaptation and survival potential for living environment and unstable weather conditions, that makes polyploidy has the selective advantage as an important species formation process. The experiment applied amplified fragment length polymorphism (AFLP) technique to analysis the genetic differences, and used methylation sensitive amplified polymorphism (MSAP) technique to anaysis DNA methylation level and heredity patterns of three loquat cultivars (Luzhou No.6, Longquan No.1 and Zaohong No.3) between different ploidy polyploids. The test provides a theoretical basis for different ploidy loquats on exploitation and ploidy breeding. It has an important reference value for the research of loquat and even plant on polyploidy process and genetic variation discipline. The primary results were as follows:AFLP analysis showed, compared with the diploid, the genome of different ploidy Luzhou No.6 loquat polyploids occurred significant changes. The total variance rate between 6% to 6.5%, band increased rate between 2.8% to 3.3% and band missing rate between 3% to 3.3%. Longquan No.1 triploid and tetraploid loquats genome total variance rate are 11% and 10.9%, band increased rate are 7.2% and 5.7%, respectively, band missing rate are 3.8% and 5.2% respectively, compared with their diploid. The total variance rate of Zaohong No.3 triploid and tetraploid loquats genome are 12.1% and 11%, band increased rate respectively are 6.9% and 6.2%, band missing rate are 5.1% and 4.8%. The results indicate all the three loquat cultivars polyploid occurred genomic variation after polyploidy.The consequences of MSAP suggested that the total methylation ratio of Luzhou No.6 triploid loquat genome are 12.8%, which higher than its diploid. However, the total methylation ratio of Luzhou No.6 tetraploid and pentaploid loquat are 11% and 12%, respectively, both lower than their diploid loquat. Both triploid and tetraploid full methylation ratio (8.5% and 8.1%, respectively) are lower than diploid(9.1%), while pentaploid full methylation ratio (9.2%) are higher than diploid. Longquan No.1 triploid total methlation ratio are 16.2%, which higher than tetraploid(14.4%) and diploid(11.4%). Longquan No.l triploid full methylation ratio(10.3%) are also higher than tetraploid(10.3%) and diploid(9.5%) full methylation ratio. Zaohong No.3 triploid loquat total methylation ratio are 15.3%, more than Zaohong No.3 tetraploid and diploid, they are 13.1% and 12.2%, respectively. The triploid has the highest full methylation ratio(11.6%), the secondary is diploid, which are 8.5%, the last one is tetraploid, the full methylation ratio are 7.9%. The three loquat cultivars, Luzhou No.6, Longquan No.1 and Zaohong No.3, when compared the methylation level of different polyploids we found triploids of all three loquat cultivars have the highest methylation level than other ploids in the same cultivar. But the total methylation level of tetraploid or pentaploid or above or below the diploid, there is no ploidy effect which displays a increase or decrease in methylation level with the polyploidy process.Comprehensive results of this study, we believed there occurred to some extent the genome DNA sequence variation and changes in methylation level and genetic pattern during the polyploidy process, but there also exist sequence difference between different ploid polyploidy. We speculated that the formation of loquat triploid heterosis related to genomic variation and re-adjustment of DNA methylation pattern, especially related to hypermethylation variation. However, chromosome doubling and the extent of DNA methylation pattern re-adjustment have some influences for the change of polyploid characters and phenotype.