Identification of pollination-induced genes from the ovary of apple (Malusdomestica)

A set of fifteen cDNA clones from apple (Malus domestica Borkh) correspondi ng to fruit genes induced or enhanced by pollination have been identified b y differential hybridization. Expression of corresponding mRNAs was induced in apple flowers by pollination, and in six clones mRNA levels also showed induction by gibberellin treatment of flowers. Sequence analysis and datab ase searches showed that these cDNAs correspond to genes involved in defenc e responses, transport, protein and flavonoid synthesis, as well as cell di vision. One of the pollination-enhanced cDNAs was found to be similar to pl ant and animal genes encoding histone H2B. This mRNA was very highly expres sed in flower buds and in fruit at early stages of development, but transcr ipt levels were relatively low in young leaves and shoot tips. RNA in situ hybridization showed histone H2B mRNA detectable at high levels in the nuce llus tissue of ovules in unopened flower buds. Five days after pollination, transcript levels decreased in the nucellus; however, weak signals were ob served in the fleshy cortex tissue.