A tomato homeobox gene (HD-Zip) is involved in limiting the spread of programmed cell death

Antisense suppression in transgenic tomato plants of H52, a gene encoding a new homeodomain protein of the HD-Zip class, produces a conditional lethal phenotype. The transgenic lines that survive exhibit spontaneous misregula tion of cell death control in leaves, which, once initiated, propagates and engulfs the entire leaf. Activation of defence genes, over-accumulation of ethylene and conjugated salicylic acid, and growth reduction of virulent p athogens also occurs in these plants. In wild-type plants, H52 is up-regula ted upon infection, mirroring the generation of the oxidative burst which n ormally precedes the hypersensitive response (HR). Thus, H52 appears to be a transcription factor involved in cellular protection by limiting spread o f programmed cell death in plants.