Temporal Expression of mRNAs after/during Fertilization in Eggplant (Solanum melongena L.) and Their Possible Involvement in Fruit Set

Abstract

Fertilization is an important event leading to fruit set. To determine when to isolate cDNAs for genes involved in fruit set in eggplant, pollen tube growth was observed under a fluorescence microscope. When tips of pollen tubes reached the ovules at the basal side of ovary within 48 hr after pollination, the cDNAs, preferentially expressed after/during fertilization, were isolated by suppression subtractive hybridization between cDNAs from pollinated and unpollinated fruits. Using cDNA macroarrays, 384 cDNA clones of the subtracted cDNA library were differentially screened by the probes of the cDNAs from pollinated or unpollinated fruit 2 days after anthesis. By Northern blot analyses, mRNAs corresponding to 11 cDNA clones were more concentrated in pollinated fruit than in unpollinated one. mRNAs corresponding to three cDNA clones, 1D05, 5D09 and 5E08 were specifically expressed in both pollinated and 4-chlorophenoxyacetic acid (4-CPA)-treated fruit 2 to 4 days after anthesis. The above 2 genes, except 1D05, were also expressed in N-(2-chloro-4-pyridyl)-N'-phenylurea (CPPU)-treated fruit 4 days after anthesis. These mRNAs were barely detected in the later stages of fruit development. 1D05 and 5D09 mRNAs were not found in leaves and stems, whereas 5E08 mRNA was detected at a very low level in young leaves and stems, but not in mature leaves. The deduced amino acid sequence of 1D05, 5D09 and 5E08 showed a similarity with cytochrome P450, hypothetical protein, and unknown protein, respectively. Expression patterns and putative function of genes corresponding to these cDNA clones, especially 1D05, lead us to speculate that they are possibly involved in the initiation of fruit set.