Evaluation of control transcripts in real-time RT-PCR expression analysis during maritime pine embryogenesis

In order to determine the suitability of reference or housekeeping genes as internal controls in real-time reverse transcriptase PCR (RT-PCR) assays for quanti. cation of target mRNAs, we studied the levels of expression of four candidate reference genes in maritime pine by real-time RT-PCR. The expression levels obtained for glyceraldehyde-3-phosphate-dehydrogenase, 18S ribosomal RNA, eukaryotic translation initiation factor eIF4AII and ubiquitin in nine stages of embryo development revealed that none of the genes tested proved to be suitable as an internal control. Copy number quanti. cation of the four transcripts showed an average relative variation of seven fold. We propose that the combination of a precise method for RNA quanti. cation, internal controls for monitoring RT reaction and PCR efficiency and a robust external standard curve can guarantee a reliable absolute quanti. cation of mRNA transcripts in real time RT-PCR. This approach may avoid the controversy in the use of housekeeping genes and may assume special significance in tissues undergoing developmental changes.