The insertion of a Mu element results in a new knotted mutation

--Richard M. Walko and Sarah Hake

A knotted mutation has arisen in a Robertson's Mutator line. This mutant exhibited mild to severe knotting as well as ligule displacement when homozygous. When outcrossed to a non-Mutator line, however, the heterozygotes exhibited very mild knotting on the first and second leaves, and then did not exhibit any knotting or ligule displacement until the last one to three leaves below the tassel. These upper leaves exhibited additional ligules displaced outward on the leaf blade and generally severe knotting.

Southern analysis indicates the insertion of an element into the Kn1 locus. The insertion is approximately 1.4kb in length with HinFI sites close to its ends in the inverted repeat regions as indicated by probing Southern blots with a probe for Mu ends, pDTE1 (V. Chandler, C. Rivin, and V. Walbot, Genetics 114:1007, 1986). While this insertion is similar to Mu1 in size and HinFI restriction pattern, this insertion contains a PvuII restriction site and does not exhibit homology to an internal fragment of Mu1 (pA/B5; Chandler et al., 1986) as indicated by Southern analysis. The insertion appears to be located in the Kn1 locus within 250 bases of the site where a Ds2 insertion occurs to cause the knotted phenotype in another mutation, Kn1-2F11 (Hake et al., EMBO in press). The insertion and its flanking sequences have been cloned and further analysis is in progress.

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