| Sweet potato [Ipomoea batatas(L.)Lam.] germplasm resources presented abundant color polymorphisms due to anthocyanin accumulation,and its anthocyanin components are the most stable similar natural extracts among plants.This color polymorphisms provided great industrial development value,such as the application of purple-fleshed sweet potato resources has brought great economic benefits to the development of the sweet potato industry.Anthocyanin accumulation was regulated by genetic and environmental factors,both varietal differences and cultivation environment affected the color presentation of plants.To analyze the main reasons for the formation of purple germplasm resources,the morphological polymorphism and genetic polymorphism related to anthocyanin synthesis were analyzed in this research.The following results were obtained1.The accumulation of anthocyanin in purple germplasm resources of sweet potato is mostly determined by genetic factors.Morphological correlation analysis revealed that the similarity of purple traits between tuber skin and absorber root,or leaf veins and vein base in sweet potato germplasm resources were more than 86%,which were developed from similar vascular tissues.The purple color of tissues(organs)such as flesh,tuber skin,stem and leaf vein were relatively independent traits that could be used as a basis for germplasm resource classification.The physiological and biochemical indicators of the anthocyanin in sweet potato purple germplasm resources were significantly different from those of non-purple germplasm resources.The purple shade was significantly positive correlated with the anthocyanin content,as the purple color of leaves is determined by the rate of accumulation of anthocyanin.The anthocyanin content in fresh of purple leaves was up to 91.5mg per 100 g.Cultivation environmental alter the content of anthocyanin in sweet potato,but it did not directly determine the formation of purple trait.The monomeric components of anthocyanins in sweet potato were cyanidin,delphinidin,pelargonidin,petunidin and peonidin,and malvidin is missing.The content of anthocyanin monomers of purple leaves was significantly higher than that of green leaves or purple flesh,with cyanidin,delphinidin and peonidin being the most abundant.The purple flesh of "Zhezi No.1" were mainly contained delphinidin and peonidin,while the tuber skin also contained a certain amount of petunidin.In addition,the content of rutin both exceeded 24.03 μg in the per 1 g fresh leaves of "Xiangcaishu No.2" and "Purple Leaf".2.Multimembers of the anthocyanin synthesis-related gene were the genetic basis for the generation of anthocyanin accumulation polymorphisms in sweet potato.The developed TRAP molecular markers were applied to the analysis of the number of gene family members,and genetic polymorphism of TRAP molecular markers were mainly appeared in upstream flanking sequences of these gene coding regions.The The copy number of upstream enzyme genes of anthocyanin synthesis pathway exceeded six,and the number of downstream enzyme genes was 1-3.A total of 13 Ib PALs,3 Ib C4 Hs,1 Ib4 CL,2 Ib CHSs,2 Ib CHIs,1 Ib F3 H,2Ib F3’Hs,3 Ib DFRs,1 Ib ANS,1 Ib ANR,15 UFGTs,and two transcripts each of IbMYB2 s and Ibb HLH2 were identified from the transcriptomic.A class of SCAR molecular markers was developed based on gene coding regions,and multiple genotypes were detected in IbMYB1,IbMYB2 s and Ibb HLH2.In addition to the IbMYB1-2a/b molecular markers that have been reported to be specific to the purple flesh,we provided a set of new molecular markers based on the IbMYB1-3 sequence which are specific to purple stems and leaves in germplasm resources.3.IbMYB1 are the key regulatory genes for the specific accumulation of anthocyanins in purple germplasm resources.Transcriptomic analysis revealed that the correlation factor between the expression of anthocyanin synthesis-related enzyme genes and anthocyanin content in sweet potato were over 90%.A large spatiotemporal expression differences exist between different members of the same gene family in the different tissues of sweet potato.The co-expression of multiple enzyme genes determined the differential accumulation of anthocyanins.156 MYBs,546 b HLHs and 354 WDRs were identified from transcriptomic by KIPEs method,the correlation factor between gene expression of IbMYB1,or Ibb HLH2,and anthocyanin content were over 90%,means IbMYB1 and Ibb HLH2 are key regulators of anthocyanin synthesis in purple germplasm resources.IbMYB2 s only expressed in leaves at low level,and not expressed in all flesh of sweet potato.Expression trends of the enzyme genes Ib CHS,Ib DFRA and Ib ANS were found to be consistent with those of the regulatory genes IbMYB1 and Ibb HLH2 by RT-q PCR analysis.Spatiotemporal expression pattern of IbMYB1 is more stringent than that of Ibb HLH2,as its expression changes occurred at the earliest stage of the regulation of anthocyanin synthesis.It means IbMYB1 is a determinant of regulation of anthocyanin-specific accumulation in purple germplasm resources.4.Functional differences in the members of IbMYB1 gene family are the underlying cause of anthocyanin-specific accumulation in purple germplasm resources.It was found that IbMYB1 was encoded by multiple members of the gene family,which reasonably explains the non-linkage of IbMYB1 gene expression in purple leaves with known members of the IbMYB1 gene family in purple germplasm resources.IbMYB1 and IbMYB2 s belong to different gene families,with the IbMYB1 family being the determinant of the regulation of anthocyanin synthesis.A new member of the IbMYB1 gene family,which named IbMYB1-3,was cloned by FNPI-PCR from purple germplasm resources.IbMYB1-3 gene is tightly linked with the purple trait of stem and leaf in the genetic segregation population.Although the IbMYB1-3gene remains a sufficient non-essential condition for the purple color of stem and leaves in natural genetic population.This research clarified the objective fact that IbMYB1 multi-gene family regulates the specific accumulation of anthocyanin in purple germplasm resources.It confirmed the inference that the accumulation of anthocyanin in purple germplasm resources is mostly a qualitative genetic trait. |
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