Stability analysis of reference genes for RT-qPCR assays involving compatible and incompatible Ralstonia solanacearum-tomato 'Hawaii 7996' interactions.

Reverse transcription-quantitative PCR (RT-qPCR) is an analytical tool for gene expression quantification. Reference genes are not yet available for gene expression analysis during interactions of Ralstonia solanacearum with 'Hawaii 7996' (the most stable source of resistance in tomato). Here, we carried out a multi-algorithm stability analysis of eight candidate reference genes during interactions of 'Hawaii 7996' with one incompatible/avirulent and two compatible/virulent (= resistance-breaking) bacterial isolates. Samples were taken at 24- and 96-h post-inoculation (HPI). Analyses were performed using the ∆∆Ct method and expression stability was estimated using BestKeeper, NormFinder, and geNorm algorithms. TIP41 and EF1α (with geNorm), TIP41 and ACT (with NormFinder), and UBI3 and TIP41 (with BestKeeper), were the best combinations for mRNA normalization in incompatible interactions at 24 HPI and 96 HPI. The most stable genes in global compatible and incompatible interactions at 24 HPI and 96 HPI were PDS and TIP41 (with geNorm), TIP41 and ACT (with NormFinder), and UBI3 and PDS/EXP (with BestKeeper). Global analyses on the basis of the three algorithms across 20 R. solanacearum-tomato experimental conditions identified UBI3, TIP41 and ACT as the best choices as reference tomato genes in this important pathosystem.