Screening and Validation of Reference Genes for Real-Time Fluorescence Quantitative PCR during Coloring Period in Apple (Malus domestica)
The change of gene expression level during coloring period is crucial for the formation of apple fruit quality. The selection of a suitable reference gene is an important factor for accurate gene expression analysis by real-time lfuorescence quantitative PCR (qRT-PCR). In this study, peels of apple (Malus domestica cv.‘Fuji’) were taken as materials sampled at different time during coloring stage. The expression level of four commonly used housekeeping genesβ-actin, EF-1α, GAPDH and 18S rRNA were studied by qRT-PCR, and reliable refer-ence gene were screened to use for gene expression during coloring stage of fruit by geNorm and NormFinder software. The results showed that the expression level of EF-1αwas highest and most stable, followed by 18S rRNA. However, the expression level ofβ-actin and GAPDH were relatively low. Meanwhile, the expression of lfavonoid-4-reductase gene (MdDFR) in the pathway of apple anthocyanin biosynthesis was analyzed, and the results indicated that the variation tendency of MdDFR was exactly consistent and presented normal distribu-tion using EF-1αand 18S rRNA as reference gene. Therefore, EF-1αand 18S rRNA are suitable reference genes and could be used to normalize mRNA levels in peel tissues of apple during coloring period.