The Role Of β-hex In Peach(Prunus Persica)Fruit Softening

β-N-Acetylhexosaminidase(β-hexosaminidase, β-hex; EC3.2.1.52)is an N-glycan processing enzyme, which acts at the late stage of the protein N-glycosylation pathway. This enzyme was recently reported to play a crucial role in the ripening-associated softening of climacteric fruit, and non-climacteric fruit. In the present study, we chose ‘Shahong’ as experimental material, cloned β-hex genes family members through the ways of RT-PCR, RACE and normal PCR. Bioinformatics analysis of β-hex genes online. And examined their expression and enzyme activity during peach fruit developmental stage and ripening and softening process. Furthermore, we also investigated the influence of cell wall degrading enzymes such as endo-PG, exo-PG, PME, and β-Gal, ethylene production and its biosynthetic gene PpACS and PpACO to understand the possible role of β-hex in the development and ripening of peach fruits. The followings are our main results:1、Two peach β-hex genes, Pphex1 and Pphex2 were cloned in the present study. Homology comparison showed that Pphex1 and Pphex2 shared very low identity both in their gene sequences and deduced amino acids. They belong to two different categories A and B in the phylogenetic analysis, and showed high identity in their relative categories, both over 60% identity. However, the similarity is very low, lower than 60% between A and B branches.2、During fruit development, the trend of β-hex activity is very similar to the expression of Pphex1, but very different with Pphex2. Both of β-hex activity and expression of Pphex1 showed high quantity in the beginning and at the end of fruit development, and relatively low quantity in the middle stage. However, the expression of Pphex2 is lower than Pphex1 in all the stage of fruit development, and only slightly increased at the late stage of fruit development.3、During fruit ripening and softening period, the activity of β-hex and the expression of Pphex1 and Pphex2 both increased according to fruit softening. After the treatment of β-hex inhibitor: 2-ADN, the expression of Pphex1 and Pphex2 were down-regulated, and this was also with the ethylene production, expression of ethylene biosynthetic genes PpACS and PpACO, and the activities of endo-PG, exo-PG and PME related to cell wall degradation, as a result, the ripening and softening process of peach fruit was declined.We suggest that β-hex is significant in peach fruit ripening and softening, and it can regulate ethylene production and the activities of cell wall degrading enzymes endo-PG, exo-PG, β-Gal and PME activities.