Study On The Mechanism Of Coloration Difference Between ’Piqiutao’ And Its Yellow-flesh Mutant

In this study,the quality-related indicators were determined,and the differences in fruit quality and nutritional value between the two flesh color peaches were compared using the mature fruits as the test materials.Then,using the spring young leaves of ‘Piqiutao’(white-flesh)and its mutant(yellow-flesh)as DNA extraction materials,the molecular identification and analysis was carried out by ISSR and SRAP molecular markers to reveal the genetic difference between ‘Piqiutao’ and its mutant from the genome level.Meanwhile,the pulp and midveins at different developmental stages were used for experimental materials,the composition and content accumulation of carotenoids were determined by HPLC method,and the transcriptional levels of key carotenogenic and metabolic genes were analysised by Real-time quantitative PCR.Combining physiology and molecular,the major determinant for the color variation between ‘Piqiutao’ and its mutant was the differential expression of CCD4.Finally,the coding region and promoter sequence of CCD4 from the two materials were cloned and analyzed,and whether the retrotransposon insertion in the intron of CCD4 was verified.The results of the study were as follows:(1)The results of mature fruit quality comparison results indicated that the mutant had better commercial traits,higher nutritional value and health care function than ‘Piqiutao’,and it was worthy of commercial extensionan.(2)Using ISSR and SRAP molecular markers,only UBC827,UBC848 and Me4-Em1 stably amplified specific bands,indicating that there were indeed differences at the level of genomic DNA between ‘Piqiutao’ and its mutant,and the genetic background and relationship were very close,therefore,the yellow-flesh mutant was the bud variant of‘Piqiutao’.(3)HPLC analysis showed that the accumulation difference of β-cryptoxanthin,α-carotene and β-carotene promoted the total content of carotenoids in the mutant to be significantly higher than that of ‘Piqiutao’,causing the flesh and midveins of the mutant to appear yellow.(4)The results of qRT-PCR showed that CCD4 strongly expressed in the flesh and vein of ‘Piqiutao’ and was always lowly expressed in the sport,which was consistent with the accumulation pattern of carotenoids.Thus,the differential expression of CCD4 was likely to be the essential reason for the significant difference in carotenoid content between the two cultivars.(5)In order to confirm the variation mechanism of CCD4 expression difference,this study cloned the coding region and promoter sequences of ‘Piqiutao’ and mutant,and verified whether there is a retrotransposon insertion in its intron.The results showed that there was no difference between ‘Piqiutao’ and its mutant.This indicated that the differential expression of CCD4 in the two peaches was not caused by the mutation of the coding region and promoter region of CCD4 and the retrotransposon insertion.