Cloning of cDNAs encoding senescence-associated genes, ACC synthase and ACC oxidase from stored snow pea pods (Pisum sativum L. var saccharatum) and their expression during pod storage

Snow pea pods (Pisum sativum L. var saccharatum), an immature-harvested commodity, undergo several detrimental changes during storage. In order to understand this postharvest-induced process, we isolated 13 snow pea pod senescence-associated (ssa) cDNAs from a 5-day stored pod cDNA library using differential screening. Sequence comparison indicated that these cDNA clones encoded proteins related to cell membrane and nutrient remobilization, to disease response-related and ribosomal proteins, and to ubiquitin-conjugating enzyme. Two clones encoded unknown and hypothetical proteins, and four clones remain without significant homologs in the translated DNA database. In addition, we also isolated 1-aminocyclopropane-1-carboxylate (ACC) synthase and ACC oxidase cDNAs (referred to as pKPAGS-2 and pKPAGO-3, respectively) from the pod cDNA library, using their corresponding reverse transcriptase-polymerase chain reaction fragments as probes. Northern blot analysis revealed that transcript levels of all ssa-cDNA underwent differential expression in pods. Five of these cDNAs were expressed solely in pod tissue. Similarly, pKPAGS-2 and pKPAGO-3 were differentially expressed in pods, increasing in parallel with those of ssa cDNAs throughout the whole period of storage, indicating that they are likely to be involved in premature senescence of stored pods at 20°C.