Abstract
Only few orthologs of animal apoptosis regulators have been found in plants. Ectopic expression of mammalian inhibitor of apoptosis proteins (IAPs) has recently been shown to affect plant programmed cell death (PCD). We identified two novel IAP-like proteins, AtILP1/2, in Arabidopsis by applying an improved motif searching method. Homologs of AtILPs were found to occur as a novel gene family in other organisms including fungi and animals. Like baculovirus IAP repeats (BIRs) in IAPs, a conserved domain necessary for interaction with caspases, ILPs contain two highly conserved BIR-like domains with a putative C2HC-type zinc finger. Phylogenetic analyses indicated that ILPs are putative paralogs of IAPs. Transient expression of HsILP1 resulted in inhibition of apoptosis in human cells (Higashi et al., 2005), suggesting that AtILP1/2 may also regulate PCD. Possible physiological functions of AtILP1/2 in regulation of PCD triggered by pathogenic elicitors (Kadota et al., 2004) will be discussed.
