Selection of Appropriate Reference Genes for Gene Expression Analysis under Abiotic Stresses in .

is a fast growing willow species with potential as a plant used for biomass feedstock or for phytoremediation. However, few reference genes (RGs) for quantitative real-time polymerase chain reaction (qPCR) are available in , thereby limiting gene expression studies. Here, we investigated the expression stability of 14 candidate reference genes (RGs) across various organs exposed to five abiotic stresses (cold, heat, drought, salt, and poly-metals). Four RGs ranking algorithms, namely geNorm, BestKeeper, NormFinder, and GrayNorm were applied to analyze the qPCR data and the outputs were merged into consensus lists with RankAggreg, a rank aggregation algorithm. In addition, the optimal RG combinations were determined with geNorm and GrayNorm. The genes that were the most stable in the roots were and . In the leaves, was the most stable, followed by and , depending on the condition tested. Conversely, and , two genes commonly used for qPCR data normalization were the least stable across all organs. Nevertheless, both geNorm and GrayNorm recommended the use of a combination of genes rather than a single one. These results are valuable for research of transcriptomic responses in different organs.