Induction of tomato defense genes by crn genes. Total RNA (15 μg) isolated from tomato 12 d after mock inoculation with a toothpick (W), or with the binary potato virus X pGR106 (V), PVX:: crn1 (crn1), PVX::crn2 (crn2),and PVX:: inf1 was sequentially hybridized with probes from the tomato PR1a and hsr201 defense-response genes. A probe from the tomato tubulin (tub) gene was used as a loading control. Note in tomato and under these experimental conditions, only PVX::crn2 induced necrotic lesions.