Identification of differentially expressed genes in a natural fruit-abscission apple, akane

Abstract

Akane is an apple cultivar which has a characteristic that lateral flowers are naturally abscised after the central flower is pollinated. However, the lateral flowers of many apple cultivars, for example Fuji cultivar, are not abscised naturally, and they are pollinated and ripe to mature fruits. So, in an orchard the lateral fruits are abscised by treatment of abscission-inducing chemical, such as sevin. I performed suppression subtractive hybridization (SSH) and dot blotting to investigate the molecular mechanism of natural abscission in cv. Akane and compare the natural abscission with chemical-inducing one in cv. Fuji. From the dot blotting, some up- or down-regulated clones were partially sequenced and homologies were searched from GenBank. In Akane lateral flowers, putative ser/thr kinase (ASK), phosphate transporter (APT), chitinase, cellulase, ribonuclease PR-10 like protein, and unknown genes were up-regulated, and cytochrome P-450 monooxygenase, hemolysin, sorbitol dehydrogenase, glycerol kinase (AGK), and unknown genes were down-regulated. In the sevin-treated Fuji flowers, putative senescence-associated protein, ribosomal protein L19, chloroplast ribosomal protein, and unknown genes were up-regulated, and elongation factor 1-α, fructose 1,6-bisphosphate aldolase, RING zinc finger protein, and unknown genes were down-regulated. From the genes searched in Akane lateral flowers and sevin-treated Fuji flowers, natural abscission and chemical-inducing one seemed to occur in different mechanism since they didn`t share any up- or down-regulated genes each other. Cellulase, chitinase and ribonuclease PR-10 were known as related in cell wall loosening and defense process at the abscission zone. Sevin treatment seemed to influence the genes related in cell survival. The expression patterns of ASK, APT, and AGK were characterized by RT-PCR. ASK and APT were up-regulated, and AGK was down-regulated specifically in Akane lateral flowers. Each gene was cloned fro...