Effects Of Dwarfing Interstock On Fruit Polyphenol And Transcription Expression Of Phloem Genes In Apple

Objective: China is a major producer of apples,and dwarfing and high-density cultivation is the current mainstream apple planting model,which can promote early flowering,increase yield,and improve fruit quality.There are two main types of stocks: dwarfing interstock and dwarfing rootstocks.Due to the intolerance of foreign imported dwarfing rootstocks to cold weather in the northern regions of China,dwarfing interstock are the main way to achieve dwarfing and high-density cultivation of apples.It is necessary to study the effect of dwarfing interstock on the polyphenol components and content of apple fruits,reveal the mechanism of interaction between rootstocks and scions of fruit trees,and investigate the effect of dwarfing interstock on the transcriptional expression of polyphenols and bark genes in apple fruits for a clearer understanding.Method: The ‘CG24’,‘SH38’,‘SH3’,‘MD001’,‘Mac9’,and ‘CX5’ were grafted on the Malus baccata(L.)Borkh.and ‘Huahong’ was grafted on six interstocks mentioned above,the self-root grafting Malus baccata(L.)Borkh.was as a control(CK).The components and contents of polyphenol in peel and flesh were analyzed at seven periods during ‘Huahong’ apple growth by using High Efficiency Liquid Chromatography and Mass Spectrometry,and the content of total phenols was determined by Folin-Ciocalteu method.The dynamic effects of six different dwarfing interstocks on the total phenols and compounds of polyphenol in ‘Huahong’ apple were studied,and it will provide basis for selection and application of apple dwarf interstocks and fruit production with high quality.High-throughput sequencing was used to investigate differentially expressed genes in the phloem tissues of two different xenograft systems,M(’Gala’/’Mac 9’/Malus baccata(L.)Borkh.)and B(’Gala’/ Malus baccata(L.)Borkh.).The molecular mechanism of dwarfing interstock on the modification of agronomic traits such as growth and development of the grafted fruit tree,early flowering and fruiting,and improvement of fruit quality is studied.Result: The main results were as follows:1.The total phenol content in the "Huahong" apple peel is much higher than that in the flesh,and both decrease gradually as the fruit develops.Different interstocks have different effects on the total phenol content of the fruit.At maturity stage,the content of total phenols in peel of ’Huahong’ from high to low was SH38 > CG24 > SH3 > CK > MD001 > CX5 > MAC9,and the flesh was MD001 > SH38 > CK >CX5 > CG24 > MAC9 > SH3.The combination of Mac9 and SH38 significantly increased fruit coloration,SH38 and MD001 could improve peel and flash polyphenol content.In conclusion,SH38 could be considered as suitable interstocks for functional cultivation of ’Huahong’ apple.2.The tree height,scion diameter,and crown width of dwarfing interstock grafted apple trees are significantly lower than those of standard rootstock trees.The RNA-seq technique was used to evaluate the impact of dwarf interstocks on the scion and rootstock in apple trees.The results showed interstocks caused apple tree dwarfing mainly by affecting the expression of genes related to GA and IAA(GH3.9,PIN1,CKI1,ARP1,GA2ox1,and GA20ox1),and they also can regulate tree photosynthesis(MADH-ME4,and GAPC were down regulated)in the scion and promote the expression of C-metabolism-related genes(AATP1,GDH,and PFK3),N-metabolism-related genes(NRT2.7,NADH,and GDH)in rootstocks.Moreover,the interstock may promote early flowering by promoting the expression of genes related to this trait(MOF1,FTIP7,AGL12,and AGL24).The interstock can also improve the expression of secondary metabolism-related genes(DX5,FPS1,TPS21,and SRG1)related to fruit polyphenols,aroma,and quality characteristics.3.After grafting with interstock,there will be differential expression of mi RNA in the tree body,with a decrease in the expression of mi R156 in the scion and mi R172 in the rootstock.Through combined analysis of mi RNA and m RNA,it is suggested that dwarfing interstock may affect the expression of genes related to starch and sucrose metabolism in the rootstock and hormone signaling pathways in the scion.This in turn affects plant growth and development,leading to stunted plant growth.Conclusion:The total phenol and polyphenol content in the apple peel is much higher than that in the flesh.The interstock SH38 significantly increases the polyphenol content in both the peel and flesh of the "Huahong" apple,while the interstock Mac9 significantly increases the anthocyanin content in the "Huahong" apple.In the multi-omics analysis,compared with the standard rootstock,the interstock Mac9 affects the expression of genes related to hormone signaling,nitrogen metabolism,carbon metabolism,and secondary metabolism in the scion and rootstock.Meanwhile,it reduces the expression levels of mi R156 in the scion and mi R172 in the rootstock.