Screening of the Rice Viviparous Mutants Generated by Endogenous Retrotransposon Tos17 Insertion. Tagging of a Zeaxanthin Epoxidase Gene and a Novel OsTATCGene

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Abstract
The rice (Oryza sativa) retrotransposonTos17 is one of a few active retrotransposons in plants and its transposition is activated by tissue culture. Here, we present the characterization of viviparous mutants of rice induced by tissue culture to demonstrate the feasibility of the use of retrotransposonTos17 as an endogenous insertional mutagen and cloning of the tagged gene for forward genetics in unraveling the gene function. Two mutants were shown to be caused by the insertion ofTos17. Osaba1, a strong viviparous mutant with wilty phenotype, displayed low abscisic acid level and almost no further increase in its levels upon drought. The mutant is shown to be impaired in the epoxidation of zeaxanthin. On the other hand,Ostatc, a mutant with weak phenotype, exhibited the pale green phenotype and slight increase in abscisic acid levels upon drought. Deduced amino acids of the causative genes ofOsaba1 and Ostatc manifested a significantly high homology with zeaxanthin epoxidase isolated from other plant species and with bacterial Sec-independent translocase TATC protein, respectively. This is the first example of transposon tagging in rice.