Disruption of AtTOR

Insertions tagging the single AtTOR locus have been identified. Two of these insertions harboring alleles tor1-1 and tor1-2 were used to study the effects of AtTOR disruption on plant development (Menand et al. 2002). Both insertions disrupt the AtTOR coding region upstream of the kinase domain and likely represent null alleles. Consistent with this hypothesis, tor1-1 and tor1-2 are re cessive to AtTOR in heterozygotes, and both mutant homozygotes showed the same phenotype.

AtTOR null mutant homozygotes are embryo lethal (Menand et al. 2002). AtTOR-/- zygotes divide to form a suspensor and embryo proper. The suspensor develops normally. Embryonic cell division occurs, but there is no pattern of cell division, daughter cells fail to gain any volume, and the embryo fails to establish an axis of polarity. Development arrests at this stage. AtTOR-/-/-endosperms (found in seeds of AtTOR-/- embryos) show severe developmental defects. Wild-type endosperm develops as a syncytium (a multinucleate cell) that contains up to 200 nuclei before undergoing cellularization. AtTOR mutant endosperm arrest with about 50 nuclei and fail to cellularize.

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