Molecular analysis of the dominant inhibitory C2 allele C2-Idf

--Udo Wienand, Irmgard Weisskirchen, Philipp Franken and Heinz Saedler

The dominant inhibitory mutant C2-Idf (colorless kernels) is allelic to C2 (Greenblatt, MNL 49:23, 1975) and decreases kernel pigmentation if crossed to a wildtype allele. Since the C2 locus has been cloned (Wienand et al., MGG 203:202, 1986) and thus C2 specific probes were available we were interested in analyzing the molecular nature of the C2-Idf mutation.

The genomic structure of the C2-Idf allele was analyzed and compared to a wildtype C2 allele by Southern experiments. With a C2 specific sequence as a probe on EcoRI digested DNA several bands light up in the C2-Idf mutant compared to a single band in wildtype DNA (Line C), indicating the presence of several C2 genes in the C2-Idf line. For further analysis of the C2-Idf allele a genomic library was prepared from homozygous C2-Idf DNA in lambda EMBL4 and screened with a C2 specific probe. Five positive clones were isolated and compared to the wildtype C2 gene isolated previously. Restriction fragment analysis and hybridization experiments showed that the C2-Idf clones contained deletions or rearrangements or the wildtype C2 gene (instead of a full size wildtype C2 gene).

Transcript analysis of the homozygous C2-Idf mutant using the C2 cDNA as a probe showed that no C2 specific transcript could be detected (in developing kernels, 30 DAP). Interestingly, besides C2, the C2-Idf mutation also affects expression of other anthocyanin genes like A1 and Bz1. In contrast no effect of the mutation on the second chalcone synthase gene, Whp (white pollen), could be detected.

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