A MEMBER OF THE TOMATO PTO GENE FAMILY CONFERS SENSITIVITY TO FENTHION RESULTING IN RAPID CELL-DEATH

Leaves of tomato cultivars that contain the Pto bacterial resistance locus develop small necrotic lesions within 24 hr after exposure to fenthion, an organophosphorous insecticide. Recently, the Pto gene was isolated and shown to be a putative serine/threonine protein kinase. Pto is one member of a multigene family that is clustered within a 400-kb region on chromosome 5. Here, we report that another member of this gene family, termed Pen, is responsible for the sensitivity to fenthion. Pen was isolated by map-based cloning using closely linked DNA markers to identify a yeast artificial chromosome clone that spanned the Pto region. After transformation with the Pen gene under control of the cauliflower mosaic virus (CaMV) 35S promoter, tomato plants that are normally insensitive to fenthion rapidly developed extensive necrotic lesions upon exposure to fenthion. Two related insecticides, fensulfothion and fenitrothion, also elicited necrotic lesions specifically on Pen-transformed plants. Transgenic tomato plants harboring integrated copies of the Pto gene under control of the CaMV 35S promoter displayed sensitivity to fenthion but to a lesser extent than did wild-type fenthion-sensitive plants. The Pen protein shares 80% identity (87% similarity) with Pto but does not confer resistance to Pseudomonas syringae pv tomato. These results suggest that Pto and Pen participate in the same signal transduction pathway.