RT-PCR detection of P69E and P69F gene expression. A, PCR products derived from amplification of plasmids containing either the P69A, P69B, P69C, P69D, P69E, and P69F ORFs with the set of primers e1 + e2 (specific for the P69E gene) and f1 + f2 (specific for the P69F gene) is shown for comparison. B, Southern blot of DNA products derived from the PCR amplification of reversed transcribed mRNA from leaf (L), stem (S), and root (R) tissue from tomato plants using the same specific sets of primers shown in A. The blots were hybridized with a radiolabeled DNA probe for each gene.