Background: Flowering plant development is wholly reliant on growth from meristems, which contain totipotent cells that give rise to all post-embryonic organs in the plant. Plants are uniquely able to alter their development throughout their lifespan through the generation of new organs in response to external signals. To identify genes that regulate meristem-based growth, we considered homologues of Raptor proteins, which regulate cell growth in response to nutrients in yeast and metazoans as part of a signaling complex with the target of rapamycin (TOR) kinase.

A predominantly plant-based family of genes encoding RNA binding proteins is defined by the presence of a highly conserved RNA binding motif first described in the mei2 gene of the fission yeast Schizosaccharomyces pombe. In silico analyses reveal nine mei2 -like genes in Arabidopsis thaliana and six in Oryza sativa. These predicted genes group into four distinct clades, based on overall sequence similarity and subfamily-specific sequence elements. In situ analysis show that Arabidopsis genes from one of these clades, TEL1 and TEL2, are specifically expressed in central zone of the shoot apical meristem and the quiescent center of the root apical meristem, suggesting that they may somehow function to maintain indeterminacy in these tissues. By contrast, members of two sister clades, AML1 through AML5, are expressed more broadly, a trend that was confirmed by Q-PCR analysis. mei2 -like transcripts with similar sequences showed similar expression patterns, suggesting functional redundancy within the four clades. Phenotypic analyses of lines that contain T-DNA insertions to individual mei2 -like genes reveal no obvious phenotypes, further suggesting redundant activities for these gene products.

Background: TOR, the target of the antibiotic rapamycin in both yeast and mammalian cells, is a potent cell growth regulator in all eukaryotes. It acts through the phosphorylation of downstream effectors that are recruited to it by the binding partner Raptor. In Arabidopsis, Raptor activity is essential for postembryonic growth. Though comparative studies suggest potential downstream effectors, no Raptor binding partners have been described in plants.

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