Fig. 5

Expression analysis of StBEL5, StPTB1/6 and POTH1 orthologues in leaf and storage root samples of the root crops: sweet potato (a), cassava (b), carrot (c), radish (d) and sugar beet (e). Transcript levels of StBEL5, StPTB1, StPTB6 and POTH1 in potato leaf and root tissues are also shown from 3-month old plants (S. tuberosum ssp. andigena) grown under long-day conditions (f). RNA was extracted from leaves and roots and RT-qPCR with gene-specific primers was used to calculate the relative amounts of RNA for each target gene. Three biological samples were measured with three technical replicates and normalized against GAPDH mRNA. The fold change in RNA levels was calculated as the 2^−ΔΔCt value [41] relative to the mean values obtained in the leaf samples (set at a value of 1.0). Standard errors of the means are shown with one, two and three asterisks indicating significant differences (p < 0.05, p < 0.01, p < 0.001, respectively) using a Student’s t-test. Because of their close sequence match (Table 1), quantification of transcripts for PTB1 and PTB6 types in the five storage roots crops was combined as PTB1/6