Identification of 1-aminocyclopropane-1-carboxylc acid synthase genes controlling the ethylene level of ripening fruit in Japanese pear (Pyrus pyrifolia Nakai)

The shelf life of Japanese pear fruit is determined by its level of ethylen e production. Relatively high levels of ethylene reduce storage potential a nd fruit quality. We have identified RFLP markers tightly linked to the loc us that determines the rate of ethylene evolution in ripening fruit of the Japanese pear. The study was carried out using sequences of two types of 2- aminocyclopropane- 1-carboxylic acid (ACC) synthase genes (PPACS1 and pPPAC S2) and a ACC oxidase gene (PPAOX1) as probes on 35 Japanese pear cultivars expressing different levels of ethylene (0.0 similar to 300 mu l/kg fresh weight/h) in ripening fruit. When total DNA was digested with HindIII and p robed with pPPACS1, we identified a band of 2.8 kb which was specific to cu ltivars having very high ethylene levels (greater than or equal to 10 mu l/ kg f.w./h), during fruit ripening. The probe pPPACS2 identified a band of 0 .8 kb specific to cultivars with moderate ethylene levels (0.5 mu l/kg f.w. /h-10 mu l/kg f.w./h) during fruit ripening. The cultivars that produce hig h levels of ethylene possess at least one additional copy of pPPACS1 and th ose producing moderate levels of ethylene have at least one additional copy of pPPACS2. These results suggest that RFLP analysis with different ACC sy nthase genes could be useful for predicting the maximum ethylene level duri ng fruit ripening in Japanese pear.