A NOVEL ZINC-FINGER PROTEIN IS ENCODED BY THE ARABIDOPSIS LSD1 GENE AND FUNCTIONS AS A NEGATIVE REGULATOR OF PLANT-CELL DEATH

Arabidopsis Isd1 mutants are hyperresponsive to cell death initiators and fail to limit the extent of cell death. Superoxide is a necessary and sufficient signal for cell death propagation. Thus, LSD1 monitors a superoxide-dependent signal and negatively regulates a plant cell de ath pathway. We isolated LSD1 via its map position. The predicted LSD1 protein contains three zinc finger domains, defined by CxxCxRxxLMYxxG ASxVxCxxC. These domains are present in three additional Arabidopsis g enes, suggesting that LSD1 defines a zinc finger protein subclass. LSD 1 is constitutively expressed, consistent with the mutant phenotype. A lternate splicing gives rise to a low abundance mRNA encoding an extra five amino-terminal amino acids. We propose that LSD1 regulates trans cription, via either repression of a prodeath pathway or activation of an antideath pathway, in response to signals emanating from cells und ergoing pathogen-induced hypersensitive cell death.