An Arabidopsis thaliana cDNA complementing a hamster apoptosis suppressor mutant

Abstract

Programmed cell death or apoptosis is a process in which unwanted cells are eliminated during growth and development. In mammals, several genes have been identified whose products are necessary to prevent entry into the apoptotic process. We have isolated a clone from an Arabidopsis thaliana cDNA library whose predicted translation product shows highly significant similarity to the mammalian defender against apoptotic death 1 (DAD1) protein. Transformation of the mutant hamster tsBN7 cells, which undergo apoptosis at restrictive temperature, demonstrates that the plant protein is as efficient as human DAD1 in rescuing these hamster cells from apoptosis. In contrast to mammals, Southern hybridisation and genomic data indicate that there are probably two genes in Arabidopsis thaliana. Northern blot analysis shows that AtDAD transcripts are present in all tissues examined, although the abundance of the transcripts is reduced in siliques during the maturation and desiccation phase of the seed. This is the first experimental proof that a homologue of an animal gene involved in apoptosis exists in plants and the first demonstration of complementation of a vertebrate mutant by a plant cDNA. Our results suggest that this process of suppression of apoptosis has been conserved in animals and plants.

Specialized Roles of the Conserved Subunit OST3/6 of the Oligosaccharyltransferase Complex in Innate Immunity and Tolerance to Abiotic Stresses

“…In plants, a distinct role in the glycosylation of proteins has been shown for STT3A and DGL1 (Koiwa et al, 2003;Lerouxel et al, 2005). Other proteins with homology to mammalian/yeast OST subunits have been identified, but their involvement in the transfer of oligosaccharides to proteins has not been reported (Gallois et al, 1997;Danon et al, 2004;Johnson et al, 2004). The importance of this protein complex for plants is also underlined by the fact that the dgl1 null alleles as well as plants completely deficient in STT3 (stt3a stt3b double knockouts) are not viable.…”

“…A mutant line with a weak dgl1 allele displayed reduced protein N-glycosylation efficiency consistent with a crucial role of DGL1 in plant OST function. In addition, Arabidopsis proteins have been identified that display significant homology to yeast Swp1p/mammalian ribophorin II (HAPLESS6 [HAP6]) and OST2/defender-against apoptotic death (DAD1 and DAD2; Gallois et al, 1997;Danon et al, 2004;Johnson et al, 2004). Arabidopsis DAD1 could rescue the apoptotic phenotype of a mutant hamster cell line, indicating a conserved function between animals and plants (Gallois et al, 1997).…”

“…In addition, Arabidopsis proteins have been identified that display significant homology to yeast Swp1p/mammalian ribophorin II (HAPLESS6 [HAP6]) and OST2/defender-against apoptotic death (DAD1 and DAD2; Gallois et al, 1997;Danon et al, 2004;Johnson et al, 2004). Arabidopsis DAD1 could rescue the apoptotic phenotype of a mutant hamster cell line, indicating a conserved function between animals and plants (Gallois et al, 1997). On the other hand, neither for Arabidopsis DAD1/DAD2 nor for HAP6 has a specific role in protein glycosylation been described so far, and their incorporation into the OST complex remains to be shown.…”

The hypersensitive response and the induction of cell death in plants

“…These pathways may be different than the ones existing in animals, since transgenic tobacco plants carrying the Bcl-X L gene do not show altered response to the TMV virus or to P. syringae . Functional homologues of the animal anti-cell death dad-1 gene (Gallois et al, 1997;Sugimoto et al, 1995) have recently been found in maize, rice and Arabidopsis, but their involvement in the HR remains to be established. Additionally, plant proteins with conserved domains of the animal ced-9/Bcl-2 protein family have yet to be described.…”

The highly conserved DAD1 protein involved in apoptosis is required for N‐linked glycosylation

“…Ce-dad-1 is 62%, AtDAD1 is 51.5%, riceDAD1 is 47.3%, and yeast Ost2p is 40%, identical to human/hamster DAD1. Except for the yeast OST2 gene, all the other homologues have been found to complement tsBN7 cells (Sugimoto et al 1995;Gallois et al 1997;T. Makishima, personal communication), indicating that the DAD1 protein is both structurally and functionally well conserved.…”