ABSTRACT: Purpose: Tomato (Solanum lycopersicum) serves as a research model for fruit development; however, while it is an important dietary source of antioxidant nutrients, the transcriptional regulation of genes that determine nutrient levels remains poorly understood. The goals of this study are to investigate dynamic changes of tomato genes during fruit development at transcription level and provides insight into the regulatory mechanism of fruit development and presents candidate transcription factors involved in secondary metabolism. Methods: The transcriptomes of fruit at seven developmental stages (7, 14, 21, 28, 35, 42 and 49 days after flowering) from two tomato cultivars (Ailsa Craig and HG6-61) were evaluated using the Illumina sequencing platform. Raw sequences were filtered and the resulting sets of clean reads were used for the following analysis by tophat and edgeR software. qRT–PCR validation was performed using SYBR Green assays Results: The average number of reads produced for each sample was 9.5 million, with the number of clean reads per sample ranging from 3.3 to 10.9 million. The number of reads that were mapped to the S. lycopersicum genome ranged from 1,786,380 to 6,780,667. A total of 26,397 genes, which were expressed in at least one developmental stage, were detected in the two cultivars, and the expression patterns of those genes could be divided into 20 groups using a K-mean cluster analysis. Gene Ontology term enrichment analysis indicated that genes involved in RNA regulation, secondary metabolism, hormone metabolism and cell wall metabolism were the most highly differentially expressed genes during fruit development and ripening. A co-expression analysis revealed several transcription factors whose expression patterns correlated with those of genes associated with ascorbic acid, carotenoid and flavonoid biosynthesis and 15 of these were validated with qRT–PCR. Correlation analysis revealed a high degree of consistency between transcript abundance determined by qRT-PCR or RNA-seq. Conclusions: Using RNA-seq analysis, the transcript abundance of a total of 26,397 genes was revealed. A total of 823 transcription factors were identified and their expression levels were compared to those of genes encoding enzymes involved in flavonoid, ascorbic acid and carotenoid biosynthesis. This revealed 20, 34 and 37 transcription factors putatively involved in the biosynthesis of flavonoids, ascorbic acid and carotenoids, respectively. This transcriptome study provides insight into the regulatory mechanism of fruit development and presents candidate transcription factors involved in secondary metabolism.
