Regulation of the expression of lipoxygenase genes in Prunus persica fruit ripening

Three genes of the lipoxygenase (LOX) family in peach (Prunus persica var. compressa cv. Ruipan 4) were cloned, and their expression patterns during fruit ripening were analyzed using real-time quantitative PCR. All of the three peach LOX genes had been expressed during fruit ripening; however, their expression patterns were significantly different. During the normal ripening of peach fruits, the expression levels of PpLox1, PpLox2 and PpLox3 increased in varying degrees accompanying upsurge of ethylene evolution. After treated by methyl jasmonic acid (MeJA), the peak of ethylene releasing occurred in advance, and the declining rate of fruit hardness was accelerated, the expression level of the three peach LOX genes in fruits markedly enhanced at the early stage of storage, but significantly decreased at the late storage stage. So, it could be suggested that all three LOXs relate to fruit ripening; however, their functions might be different. PpLox1 expression increase along with the upsurge of ethylene evolution in both control and MeJA-treated peach fruits suggested that PpLox1 probably played a major role in the peach fruit ripening. Expression peak of PpLox2 appeared at the 1 DAH (days after harvest) in both control and MeJA-treated peach fruits, while obvious changes in ethylene evolution and fruit hardness was not observed, which suggested that the rise of PpLox2 expression can be induced by certain stimulation related to ripening, such as harvesting stress and MeJA treatment. The expression of PpLox3 kept a lower level in the natural ripening fruits, whereas raced up at the early stage of storage in the fruits treated with MeJA, which indicated that PpLox3 was expressed inductively and had minor roles during the normal ripening of peach fruits, but when encountered with external stimulation, its expression level would rapidly enhance and accelerate the ripening of peach fruit.