A spiking strategy facilitates housekeeping selection for RT-qPCR analysis under different biotic stresses in eggplant.

Endogenous housekeeping genes are traditionally employed to normalize the expression of target genes in RT-qPCR studies. Assuming that a perfect housekeeping suitable for every condition does not exist, expression stability of the chosen reference gene should be evaluated at every new experiment. The housekeeping selection process reveals furthermore complicated and time-consuming when different conditions have to be compared in the same experimental dataset. As an alternative strategy, we spiked an external reference transcript (ERT) into all RNA samples of our dataset (eggplant roots subjected to different biotic stresses), and used it to normalize the expression levels of native candidate housekeeping. ERT expression resulted highly stable across all samples and enabled to indicate glyceraldehyde 3-phosphate dehydrogenase (GAPDH) as the most stable endogenous housekeeping. This result was confirmed by the use of GeNorm, Normfinder, and BestKeeper algorithms. This method might be generally applied to expedite the selection process of the best reference gene.