Characterization of Overexpressed cDNAs Isolated from a Hormone-Autonomous, Radiation-Induced Tumor Tissue Line of Arabidopsis thaliana

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Abstract
To investigate the molecular mechanisms of hormonal control of growth, we constructed a subtracted cDNA library enriched for sequences expressed more in a hormone-autonomous, radiation-induced tumor tissue line of Arabidopsis thaliana than in normal, hormone-dependent callus. Ten cDNA clones, which are expressed 1.3- to 10-fold more in the tumor line, were isolated and partially characterized. The clones differ greatly in their level of expression in tumor tissue and in their pattern of expression in plant organs. Southern blot hybridization and sequence analysis showed that this group contains three pairs of closely related clones. Northern blot analysis indicates that one pair of clones represents two members of a gene family that are expressed in different plant organs. One of the isolated sequences shows strong sequence similarity to a cDNA encoding a lipid transfer protein. Two sequences are highly similar to those of previously described membrane channel proteins but have different organ specificities. Two other cDNAs have significant sequence similarity to glycine-rich proteins and hydroxy-proline-rich glycoproteins. When used to probe Southern blots, none of the cDNAs identified polymorphisms between tumor and callus DNA, which might be expected if their overexpression were due to local genome rearrangements induced by radiation. The diversity observed among these 10 clones suggests that some are likely to be involved in tumorous growth and not simply specific to a certain cell or tissue type present in the tumor.