CPR5 is involved in cell proliferation and cell death control and encodes a novel trans membrane protein

Plants often respond to pathogens by sacrificing cells at the infection sit e. This type of programmed cell death is mimicked by the constitutive patho gene response5 (cpr5) mutant in Arabidopsis in the absence of pathogens, su ggesting a role for CPR5 in programmed cell death control [1]. The analysis of the cellular phenotypes of two T-DNA-tagged cpr5 alleles revealed an ad ditional role for CPR5 in the regulation of endoreduplication and cell divi sion. In cpr5 mutant trichomes, endoreduplication cycles stop after two rou nds instead of four, and trichome cells have fewer branches than normal. Ev entually, cpr5 trichomes die, the nucleus disintegrates, and the cell colla pses. Similarly, leaf growth stops earlier than in wild-type, and, frequent ly, regions displaying spontaneous cell death are observed. The cloning of the CPR5 gene revealed a novel putative transmembrane protein with a cytoso lic domain containing a nuclear-targeting sequence. The dual role of CPR5 i n cell proliferation and cell death control suggests a regulatory link betw een these two processes.