Triploid Induction And Analysis Of MiRNA Expression Pattern In Hybrids Of Sect.Aigeiros

Tree species in Sect.Aigeiros play an important role in genetic improvement of poplar and are excellent resources of tree species all over the world.Many hybrid clones of sect.Aigeiros have widely generalized in North of China because of their outstanding characters.Some triploids in Sect.Aigeiros have significant practical value because they have a higher growth rate and stronger stress resistance which make them adapt to environment better.Besides,polyploidization as a crucial approach in plant evolution and speciation makes artificial induction of polyploids gains new value in theoretical research.In conclusion,artificial induction of polyploids in Sect.Aigeiros and researches on their heredity and variation have important ptactical and theoretical significance.In this research,technology system of colchicine induction on 2n pollen and high temperature induction on embryo sac in Sect.Aigeiros were optimized.And material system of polyploid group in hybrids of Sect.Aigeiros was obtained?including two parents,polyploidy offspring and diploidy offspring?.Variation of sRNA between triploid group and diploid group in Sect.Aigeiros was detected.The results provide genetic improvement in Sect.Aigeiros material and theoretical basis,and enrich the evolutional and speciational theories in xylophyta.The main results were as follows:?1?Correlation between meiotic process of pollen mother cell and external form of catkin in Poplus nigra L.and its varietas was studied which provided cytological basis for determination of treatment stage in subsequent colchicine induction of 2n pollen.The results indicated that meiotic process in poplus nigra and its varietas occured early which was completed before external form of catkin changed obviously.Because of this condition,determination of meiotic process in Poplus nigraL.and its varietas was not able to connect with external form of catkin.Besides,meiotic process of pollen mother cell was asynchronous which made peak removing and extension of colchicine action time necessary to avoid negative influence to yield of 2n pollen.?2?It was the first time to obtain high rate of 2n pollen?87.11%?which can use to cross breeding in protospecies of Sect.Aigeiros.This rate of 2n pollen beyond the previous research on protospecies approximated some induction results in hybrids of poplus which demonstrated that protospecies of Sect.Aigeiros can obtain high rate of 2n pollen used to cross breeding by colchicine The result showed that the ultimate best treatment combination was obtained as using 0.6%colchicine to inject peak-removed floral buds in pachytene 5 times every 3 hours?3?Meiosis and embryo sac development processes after pollination in P.simonii Carr x P.nigra var.Italica?Moench.?Koehne were observed via conventional paraffin method which provided cytological basis to determination of induction period in subsequent embryo sac induction with high temperature after pollination.The results showed that asynchronism also existed in meiosis and embryo sac development of oogametes after pollination which made polyploid induction possible.Statistical data of development stages of megaspore mother cells or embryo sacs at different times after pollination indicated that megaspore mother cells completed meiosis at 60h after pollination and three mitosises during embryo sac development at 120h after pollination.?4?11 triploids and 1 tetraploid in P.simonii Carr x P.nigra var.Italica?Moench.?Koehne were sucessfully obtained using embryo sac treated by high temperature.The best treatment combination was 41 ? exposure for 2 hours at 66 hours after pollination.?5?sRNA libraries in hybrids of Sect.Aigeiros were analyzed and differences between triploids and diploids were compared.The results indicated that fuction and regulation towards targets of sRNAs in Sect.Aigeiros showed diversity.Novel miRNAs in 4 triploid libraries and male parent library were bound with AG04 and probably participated in DNA methylation regulation of transposons and repeats.A novel miRNA named novel₁24 was found to probably relate with regulation of transposons and repeats methylation expression quantities of which were down regulated more than one order of magnitude that meaned this regulatory pathway may be activated.Differential target genes between triploid and diploid libraries were enriched at ADP binding in molecular function category which indicated that variation of miRNA regulation net after genome duplication mainly affected the molecular fuction of target genes.Enrichment pathway of differential target genes was plant-pathogen interaction which showed that polyploidization may affect disease resistance of polyploidy offsprings.