Gene Expression is Highly Regulated in Early Developing Fruit of Apple

An oligonucleotide-based microarray for apple was developed consisting of ~40,000 sequences, along with positive and negative controls, obtained from 34 cDNA libraries constructed from both vegetative and reproductive tissues at different stages of development, varying genotypes, and under different biotic and abiotic stresses. This apple microarray was used to investigate global gene expression profiles in early developing fruit of three apple genotypes, including "Golden Delicious", "Gala", and "Fuji". A set of 3,348 genes, exhibiting significant differential expression profiles among the three different genotypes, was identified. This set primarily included genes encoding enzymes involved in metabolism and genes related to cell cycle. Differentially expressed genes were grouped into 17 functional categories. Quantitative real-time reverse-transcription polymerase chain reaction (qRT-PCR) confirmed differential expression for most genes detected in the microarray analysis, particularly those involved in cell division, cell expansion, and cell enlargement. Among those genes investigated, EF-1 alpha and PRP exhibited differential expression in different apple genotypes and demonstrated a regulatory role during early fruit development. Moreover, a total of 12 differentially expressed genes were identified during early fruit development in three genotypes of apple. These included genes encoding for aminotransferase family protein, DnaJ heat shock, histone, rubisco activase, and tetratricopeptide (TPR) repeat containing protein. This genome-wide analysis suggested that genes engaged in early fruit development among different genotypes of apple are highly regulated.