Plant Gene Expression Center

Terminal ear mutants isolated from Mutator lines

--Edward Robbie, Bruce Veit, Paul Chomet and Sarah Hake

Two independent terminal ear mutants were found in lines carrying Robertson's Mutator elements. The phenotype of the first isolate, found in a transposon tagging experiment, is pleiotropic, with the most striking effect on the internodes. Severely affected plants are extremely stunted and two-dimensional, with the leaves emerging strictly 180 degrees apart. Less severe plants vary in their internode length, often alternating between short and long internodes, to produce plants that appear to have opposite phyllotaxy. Variability in phyllotaxy sometimes gives plants with successive leaves that arise from one side of the plant. The tassels are often feminized. Either the lower tassel branches are somewhat feminized or, alternatively, they may be transformed into entire ears enveloped in husks. Usually the entire tassel is enclosed in husks and rarely it is a completely feminized, unbranched inflorescence. The second mutant with a similar phenotype was discovered by Paul Chomet in his Mutator lines. Crossing of the two mutants showed that they were allelic.

Morphological analysis suggested that the new mutants could be alleles of terminal ear (te1). We determined that our allele, te1-sn, was allelic to the reference allele, te1-R by crossing the two together. We also uncovered the phenotype by crossing te1-sn by TB-3La. The reference allele is also uncovered by TB-3La according to J. Beckett. We are in the process of mapping terminal ear more closely.

We investigated the possibility of linkage of the te1-sn phenotype with a Mutator element. Genomic DNA from families segregating for te1-sn were digested with BclI, blotted and hybridized to the internal portions of Mu8 and Mu1. Upon analysis of over sixty chromosomes, tight cosegregation of a Mu8 element with the mutant phenotype was demonstrated. We determined that a fragment of the same size is segregating with the mutant phenotype in the line of Paul Chomet's. Because these two mutants do not share progenitors, it suggests that two different Mu8 elements may have inserted in the same BclI fragment. We are in the process of cloning this BclI fragment in order to determine if it is part of the terminal ear locus.

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