Selection of appropriate reference genes for gene expression studies by quantitative real-time polymerase chain reaction in cucumber.

Quantitative real-time polymerase chain reaction (QRT-PCR) has become one of the most widely used methods for gene expression analysis. However, the expression profile of a target gene may be misinterpreted due to unstable expression of the reference genes under different experimental conditions. Thus, a systematic evaluation of these reference genes is necessary before experiments are performed. In this study, 10 putative reference genes were chosen for identifying expression stability using geNorm, NormFinder, and BestKeeper statistical algorithms in 12 different cucumber sample pools, including those from different plant tissues and from plants treated with hormones and abiotic stresses. EF1alpha and UBI-ep exhibited the most stable expression across all of the tested cucumber samples. In different tissues, in addition to expression of EF1alpha and UBI-ep, the expression of TUA was also stable and was considered as an appropriate reference gene. Evaluation of samples treated with different hormones revealed that TUA and UBI-ep were the most stably expressed genes. However, for abiotic stress treatments, only EF1alpha showed a relatively stable expression level. In conclusion, TUA, UBI-ep, and EF1alpha will be particularly helpful for reliable QRT-PCR data normalization in these types of samples. This study also provides guidelines for selecting different reference genes under different conditions.