The Difference Of Ethylene Biosynthesis And Expression Of Softening-related Genes Between ‘shahong’ And ‘qinwang’

The peach cultivar ‘Qinwang’(Prunus persica cv.Qinwang) has a good storage property. But, it is very different from the never-ripe peach mutant ‘stony hard’, ‘Qinwnag’ softens gradually with juice increasing, then becomes palatable and meets consumers’ demand after 20 d. So, ‘Qinwnag’is a ideal material for studying fruit ripening and softening and breeding long shelf-life peach cultivar. However, the mechanism of long shelf-life of Qinwang is not clear. 1-aminocyclopropane-1-carboxylic acid synthase(ACS) plays a key role in regulating ethylene production and fruit ripening, however, there are very few researches about how ACS gene family members work in regulating ethylene biosynthesis during fruit development. In order to make it clear that why ‘Qinwang’could keep a good quality for a long time, and how ACS gene family control ethylene production during fruit development and ripening periods, we analysed ethylene production and softening-related genes expressions between two peach cultivars ‘Qinwang’ with good storage property and ‘Shahong’(Prunus persica cv.Shahong) with poor storage property fruits harvested at commercial maturity. Whats more, we investigated the ACS gene family expressions in ‘Jingchun’(Prunus persica cv.Jingchun). Results are as follows:1.‘Shahong’softened quikly along with lots of ethylene production. ‘Qingwang’ remained high firmness during storage accompanied by a quite low ethylene production rate. PpACS1 increased significantly during ‘Shahong’softening, however, it was inhibited in ‘Qinwnag’. 1-aminocyclopropane-1-carboxylic acid oxidase gene(PpACO1) also increased in ‘Shahong’ but did not in ‘Qinwnag’. Results indicated that the delay of ‘Qinwang’ fruit softening was due to the lack of enough ethylene eproduction by limiting expression of PpACS1.2. The expression of expansion(EXP) gene PpEXP increased at first and then decreased in two peach cultivars, but it was very low in ‘Qinwang’ compared with ‘Shahong’. The expression pattern of pectin methylesterase gene(PpPME) and polygalacturonase gene(PpPG) were extremely similar. Both of them increased accompanied with ‘Shahong’ softening especially in the late storage. Whats more, they were extremely low in ‘Qinwang’. Results indicated that EXP may play a role in early ripening then PME and PG influence fruit ripening later. In ‘Qinwnag’, the inhibition of PpEXP and PpPG expressions causes the declay of pectins can not degrading, in return, peach fruits can not soft.3. N-glycan processing enzymes α-mannosidase gene(Ppα-Man) and β-hexosaminidase gene(PpHex1 and PpHex2) expression levels were low in ‘Shahong’ than ‘Qinwnag’. α-Man and β- Hex may not be key factors acting on ‘Qinwang’ softening.4. We compared nectarine genome sequences with ACS proteins from other species using BLASTp, 4 ACS gene were selected, respectively were Pp022214m、Pp015636m、Pp016458m、Pp004987m. All the PpACS isozymes contained seven conserved boxes found in ACS. Eleven amino acid residues conserved in ACS proteins, and the glutamate(E) residue in box 1 responsible for substrate specificity present in all of the ACS sequences.5. The expression parterns of the 5 ACS genes including PpACS1 were different. We did not detected Pp022214 m and Pp015636 m expressions during ‘Jingchun’ development and ripening; Pp016458 m increased in S2, decreased fast in S3 then stoped with very low expression; Pp004987 m showed no expression in S2, increased after S3 and reached a peak in the second day during storage; PpACS1 showed no expression in S2, then inceased significantly after S3 with two peak respectively in the second day and sixth day during storage. The expression of Pp004987 m and PpACS1 were ripening specific, whats more, PpACS1 expression level was significantly higher than Pp004987 m. Pp016458 m may responsible for system Ⅰof ethylene synthesis, Pp004987 m and PpACS1 maybe in charge of system Ⅱethylene. And PpACS1 is the main factor in ethylene synthesis.6. We also investigated the expression of ACS gene family in ‘Shahong’ and ‘Qinwang’ during storage. The expressions Pp022214m、Pp015636m and Pp016458 m were not detected in ripe fruits. PpACS1 expression level kept increasing in ‘Shahong’ and was much higher than that of ‘Qinwnag’. In ‘Qinwang’, it increased slowly before 21 d, later, rapidly increased. The expression of Pp004987 m was not detected in the two peach cultivars. Results further suggested the inhibition of PpACS1 expresion lead to ethylene deficiency.