Isolation of cDNAs for genes expressed after/during fertilization and fruit set of melon (Cucumis melo L.)

Abstract

Fertilization is an important event leading to fruit set. Tips of pollen tubes reached the ovules at the base of the ovary within 24 hr after pollination. Therefore, cDNAs for genes 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 1 day after anthesis. By Northern blot analyses, mRNAs, corresponding to 14 cDNA clones, were more concentrated in pollinated fruit than in the unpollinated ones. The deduced amino acid sequence of genes corresponding to these cDNA clones showed a similarity with ascorbate oxidase, hydroxymethyltransferase, phosphoethanolamine N-methyltransferase, short chain alcohol dehydrogenase, histone H2A, auxin binding protein, 14-3-3 protein, extensin-like protein, nucleoid DNA-binding-like protein, type IIIa membrane protein (reversibly glycosylated polypeptide), and hypothetical proteins. In melon, N-(2-chloro-4-pyridyl)- N′-phenylurea (CPPU) induced parthenocarpy without pollination, whereas 4-chlorophenoxyacetic acid (4-CPA) was less effective on producing parthenocarpic fruit. mRNAs corresponding to 14 cDNA clones were expressed in both pollinated and CPPU-treated fruit. Expressions of mRNAs corresponding to all cDNA clones in pollinated and CPPU-treated fruit were higher than those in 4-CPA-treated fruit. These mRNAs were barely detectable in the later stages of fruit development and were expressed preferentially in fruit except for 6E04 and 6H01. Especially, expression patterns of 8A07 (nucleoid DNA-binding-like protein) and 8D10 (short chain alcohol dehydrogenase) lead us to speculate that they play important roles in fruit set because they are expressed at a higher level in the early stages of both pollinated and CPPU-treated fruit than that of 4-CPA-treated fruit.