References genes for qRT-PCR in guaraná (Paullina cupana var. sorbilis)

Gene expression has been extensively studied in plant science research, mainly for the assessment of plant stress responses. Real-time-quantitative polymerase chain reaction (RT-qPCR) is an important tool for obtaining this information because it is a quick and easy technique to acquire a large amount of molecular data for both model and non-model plants. For a successful RT-qPCR analysis, gene expression should be carefully normalised. Genes involved in essential biological processes that exhibit constitutive expression are commonly selected as internal standards to normalise RT-qPCR experiments. In this study, the transcription profiles of 13 candidate reference genes for RT-qPCR were evaluated in three guarana cultivars (BRS-Amazonas, BRS-Maués and BRS-Luzéia) using different tissues (vegetative and fruit) in varying developmental stages. Two different algorithms, NormFinder and GeNorm, were utilised to assess gene stability. In general, the two algorithms did not select the same pairs of genes for all analysed conditions. For the largest group (the fruits of all cultivars), NormFinder selected the pair EF1A/UBQ, whereas GeNorm chose ACT/GAPDH as the best normalising genes. Thus, we recommend the use of at least four reference genes for the normalisation of gene expression in guarana plant studies.