Differential Analysis Of Exocarp Structure And Component Of Suberin And Protein Between Exocarp Of ‘Xiangnanli’ Pear And Its Green Shine Mutant

The color of fruit skin is an important agronomic trait and economic trait in pear.‘Xiangnanli’ pear fruit has a russet skin while its mutant ‘Qingpixiangnanli’ pear has a green yellow fruit skin.To further study the formation mechanism of ‘Xiangnanli’russet skin,the exocarps of ‘Xiangnanli’ pear and its green yellow mutant‘Qingpixiangnanli’ at different stages were used and the fruit chromatism and hardness were measured.The fruit epidermal structure was also determined by microscope and electron microscope.The composition of phenolic compound and suberin of fruit exocarp were mensurated by the high performance liquid chromatography(HPLC)and the gas chromatography mass spectrum(GC-MS).The relative expressions of the key genes on pear skin colour by proteome were analyzed by using quantitative real-time PCR.The main results were as followed:(1)With the development of fruit,the chromatism between ‘Xiangnanli’ and‘Qingpixiangnanli’ increased,and the fruit hardness of ‘Xiangnanli’ were harder than that of ‘Qingpixiangnanli’;The cuticular wax layer of ‘Qingpixiangnanli’ was thicker than that of ‘Xiangnanli’.There were less suberized cells in the exocarp of‘Qingpixiangnanli’,while those of two pears fruit were found through the development of fruit.The thickness of ‘Xiangnanli’ and ‘Qingpixiangnanli’ fruits cuticle had the same changed,and increased at first and then decreased.(2)There were 12 kinds phenolic compounds in the exocarp of ‘Xiangnanli’ and‘Qingpixiangnanli’: arbutin,gallic acid,catechin,chlorogenic acid,caffeic acid,vanillin,L-epicatechin,coumalic acid,ferulic acid,naringin,phloridzin and cinnamic acid.The contents of arbutin and ferulic acid decreased with the development of fruit in two pears.The gallic acid,catechin,caffeic acid and phloridzin content increased at first and then decreased in two pears with the highest value at 75 days after full bloom(DAFB).(3)The results indicated that suberin in the exocarp of ‘Xiangnanli’ and‘Qingpixiangnanli’ was composed of fatty acid,α,ω-diacids,ω-hydroxy fatty acids,mainly ferulic acid and primary alcohols.During all the stage of fruit development,fatty acids were the main components of fruit suberin.But at the late stage of fruit development,the content of fatty acids decreased sharply.At the 25 DAFB,the content of fatty acids in the exocarp of ‘Xiangnanli’ was higher than that in‘Qingpixiangnanli’,while at the other two stages the content was inversed.Only at the early stage of fruit development,the content of ω-hydroxy fatty acid in‘Qingpixiangnanli’ was about two times higher than that in ‘Xiangnanli’.The primary alcohols appeared at 75 DAFB in two pears,and the content was very similarity.With the pear fruit development,the contents of α,ω-diacids and ferulic acid in the exocarp of ‘Xiangnanli’ were higher than that in ‘Qingpixiangnanli’ with about three times at75 DAFB.(4)We analyzed the protein expression profile by i TRAQ technology.There were181 variant proteins between ‘Xiangnanli’ and ‘Qingpixiangnanli’ fruit exocarp,while there were 98 up-regulated proteins,21 of them involved with suberin and 83down-regulated proteins,11 of them involved with suberin.The Fold change> 1.2and Q-value < 0.05 were used for the rule to sure which protein was the variant proteins.By GO and GOG Pathway annotation analysis,the proteins between‘Xiangnanli’ and ‘Qingpixiangnanli’ fruit exocarp were found to be involved 10 kinds cellular component,6 kinds of molecular function and 17 kinds of biological process,and involved in 137 metabolic pathways.For the differential expression proteins Pathway enrichment analysis,metabolic pathway and biosynthesis of secondary metabolites had the most variant proteins.Choosing 8 gene sequences for RT-PCR verification,which 4 up-regulated proteins and 4 down-regulated proteins,the result showed that expression of Pp ACC、PpβAS、Pp FAR and Pp SDR in the exocarp of ‘Xiangnanli’ was higher than that in‘Qingpixiangnanli’ at 75 DAFB.The expression of Pp ECR、Pp LTPs and Pp GDSL in‘Qingpixiangnanli’ was higher than that in ‘Xiangnanli’ at 75 DAFB.The protein expression spectrum data was real and reliable.