Selection of Differentially Expressed Genes Responding to High Temperatures in 'Fuji' Apple Tree Leaves by a Transcriptome Analysis

A transcriptome analysis was conducted to select differentially expressed genes (DEGs) from 'Fuji' apple tree leaves exposed to high temperatures (35 degrees C) for 24 hours. A total of 34,158,132 and 41,475,948 paired-end reads for 25 degrees C and 35 degrees C samples of 'Fuji' apple tree leaves were obtained, respectively. The average read-length ranged from 90.0 to 90.2 bp and the analyzed reads were found to cover 82.8-83.1% of the raw data. DEGs were divided into 15, 11, and 30 main functional categories of molecular functions, cellular components, and biological processes with different degrees at level 3, respectively. The major up-regulated genes included a GDSL-like lipase/acylhydrolase superfamily protein, a cell wall protein precursor, MLP-like protein 423, heat shock protein 18.2, a HSP20-like chaperones superfamily protein, phytosulfokine receptor 1, a protein phosphatase 2C family protein, and microsomal glutathione s-transferase, while the major down-regulated genes included 3-ketoacyl-CoA synthase 19, a cysteine proteinase superfamily protein, the plant invertase/ pectin methylesterase inhibitor heat shock protein 70, ferretin 1, nitrate transporter 1.7, and heat shock protein 81-2 in apple leaves exposed to high temperatures. The selected DEGs were confirmed to be differentially expressed by high temperatures in a quantitative real time-PCR analysis with gene-specific primers. Transcriptome data can provide meaningful information about the discovery of specific gene and can elucidate the mechanism in apple trees responding to high temperatures, and selected DEGs can be used as genetic resources in the molecular breeding of apples tolerant to foreign stress sources such as high temperatures in the future.