Genome-wide isolation and expression analysis of vacuolar processing enzyme (VPE) gene family in four apple cultivars with different storability

This research was undertaken to determine expression patterns of vacuolar processing enzyme (VPE) genes in four apple (Malus domestica (Suckow) Borkh) cultivars 'Royal Gala (RG)', 'Golden Delicious (GD)', 'Ralls Janet (RJ)' and 'Fuji (FJ)' during ripening. The results showed that GD and RG had higher respiration rate, ethylene production, content of malondialdehyde (MDA), relative electrical conductivity (REC) and VPE activity than RJ and FJ during ripening. A total of 17 MdVPEs were found to be expressed in four cultivars. These MdVPEs exhibited different expression patterns during ripening of four cultivars. Generally, MdVPE beta 1, MdVPE gamma 2, MdVPE gamma 4 and MdVPE delta 7 might be closely associated with ripening of all cultivars. MdVPE alpha 6 might have a role in the early period of ripening of ACS1-2/-2 (1-Aminocyclopropane-1-carboxylate synthase) homozygous cultivars (RG, RJ and FJ). Our data here would be helpful in understanding the associations between MdVPEs and storage properties of different apple cultivars.