Reference gene selection for real-time quantitative polymerase chain reaction normalization in "Swingle" citrumelo under drought stress.

We describe the first systematic evaluation of reference genes for use in real-time quantitative polymerase chain reaction (qPCR) for water deficit stress studies in the citrus rootstock "Swingle" citrumelo. The expression levels of seven reference genes-cyclophilin (CYP), cathepsin (CtP), actin (ACT), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), elongation factor 1alpha (EF1alpha), beta-tubulin (TUB), and ADP ribosylation factor (ADP)-during drought stress were tested using geNorm and NormFinder programs. Results from four experimental conditions indicated that EF1alpha and ADP were the most stable reference genes. Relative expression levels of Delta1-pyrroline-5-carboxylate synthetase (P5CS) was used for reference gene validation.