Studies On Characteristics And Genetic Components Of Interspecific Somatic Hybrids Between Sweetpotato(Ipomoea Batatas(L.)Lam.) And Its Wild Relatives

Sweetpotato(Ipomoea batatas(L.)Lam.)is an important root crop and planted widely in more than 100 countries,most of which locate in the tropics and subtropics.Its wild relatives contain many useful and desirable genes lacking in the cultivated sweetpotato.However,gene transfer from these wild species to sweetpotato through sexual hybridization is usually difficult due to the cross-incompatibility between sweetpotato and its wild relatives.It is shown that somatic hybridization can be used to overcome the cross-incompatibility and transfer desired characteristics from wild relatives to cultivated plants.In the present study,characteristics and genetic components of somatic hybrids,XT1(Xushu18+I.triloba),KT1(Kokei No.14+I.triloba)and XL1(Xushu 18+I.lacunosa),between sweetpotato and its wild relatives were systematically studied for the development and application of useful genes from the wild relatives.The main results are as follows:1.The somatic hybrid XT1 was characterized through RAPD,cytological and morphological analyses.XT1 exhibited significantly higher drought tolerance compared to Xushuls.Proline content and superoxide dismutase(SOD),catalase(CAT)and photosynthesis activities were significantly increased,while malonaldehyde(MDA)content was significantly decreased in XT1 compared to Xushu 18 under drought stress.It was also showed that the soluble sugar and protein content were significantly higher in XT1 than in Xushu 18.Simple sequence repeats(SSR)and amplified fragment length polymorphism(AFLP)analyses indicated that XT1 had genomic DNA band patterns consisting of both parent specific bands and changed bands.Methylation-sensitive amplified polymorphism(MSAP)analysis showed that XT1 had DNA methylation site patterns consisting of both parent specific sites and changed sites.Further analysis demonstrated that XT1 had the much higher proportions of Xushu 18 specific genomic DNA bands and methylation sites in comparison with those of I.triloba.Transcriptome analysis indicated that XT1 retained similar gene expression patterns to Xushu 18.Cytoplasmic genome analysis revealed that XT1 had the same chloroplast and mitochondrial genomes as Xushu 18.RNA-seq and real-time quantitative PCR(qRT-PCR)analyses showed that the well-known drought stress-responsive genes in XT1 and I.triloba were significantly up-regulated under drought stress.2.The somatic hybrid KT1 exhibited significantly higher drought tolerance compared to Kokei No.14.Proline content and SOD,CAT and photosynthesis activities were significantly increased,while MDA content was significantly decreased in KT1 compared to Kokei No.14 under drought stress.SSR and AFLP analyses showed that KT1 had genomic DNA band patterns consisting of both parent specific bands and changed bands.MSAP analysis indicated that KT1 had DNA methylation site patterns consisting of both parent specific sites and changed sites.Further analysis demonstrated that KT1 had the much higher proportions of Kokei No.14 specific genomic DNA bands and methylation sites compared to those of I.triloba.Transcriptome analysis indicated that KT1 retained similar gene expression patterns to Kokei No.14.Cytoplasmic genome analysis revealed that KT1 had the same chloroplast and mitochondrial genomes as Kokei No.14.RNA-seq and qRT-PCR analyses showed that the well-known drought stress-responsive genes in KT1 and I.triloba were up-regulated under drought stress.3.The somatic hybrid XL1 exhibited significantly higher tolerance to heavy metal aluminum(Al3+)and chromium(Cr6+)toxicity stresses compared to Xushu 18.Proline content and SOD and CAT activities were significantly increased,while MDA content was significantly decreased compared to Xushu 18 after exposure to various concentrations of Al3+ and Cr6+.SSR and AFLP analyses showed that XL1 had genomic DNA band patterns consisting of both parent specific bands and changed bands.MSAP analysis indicated that XL1 had DNA methylation site patterns consisting of both parent specific sites and changed sites.Further analysis demonstrated that XL1 had the much higher proportions of Xushu 18 specific genomic DNA bands and methylation sites compared to those of I.lacunosa.Cytoplasmic genome analysis revealed that XL1 had the same chloroplast and mitochondrial genomes as Xushu 18.These results unequivocally demonstrate the significance of somatic hybridization techniques in the genetic improvement of sweetpotato,and will aid in exploring the useful genes of I.triloba and I.lacunosa and understanding the evolution and phylogeny of the cultivated sweetpotato.