Structure and function of different C1 alleles

--Brian Scheffler, Philipp Franken, Elvira Tapp, Andreas Schrell, Heinz Saedler and Udo Wienand

In addition to the wildtype C1 and mutant C1-I allele analyzed previously (Paz-Ares et al., EMBO J. 6:3553-3558, 1987; Paz-Ares et al., EMBO J. 9:315-321, 1990) further C1 alleles have been cloned and sequenced. Among those were the over-expressing allele C1-S, the light inducible allele c1-p, the recessive allele c1-n, and the Ds element induced allele c1-m1 (a genomic clone of c1-m1 was kindly provided by K. Cone, K).

The coding region of C1-S and c1-m1 is very similar to that of the wildtype C1 allele, whereas the c1-p and c1-n alleles show several sequence differences. In the c1-p allele these lead to various amino acid changes and in the c1-n allele to a frame shift mutation. Major sequence differences between the C1 alleles have been detected in the region 3' of the codogenic sequence. There, three deletions (455bp, 1159bp, 216bp) are present in the c1-p allele. The C1-I allele seems to have a deletion identical in size and position to the 455bp deletion present in c1-p.

The promoter sequences of the c1 alleles analyzed are very homologous (up to position -600) and differ only in two short footprint like sequences (boxI and boxII) close to the putative CAAT box. Little sequence alterations (insertions and deletions) in these boxes may be correlated with the different expression patterns of the alleles. This assumption is supported by particle gun experiments. The full length C1 promoter and deletion products thereof were fused to the luciferase gene and delivered into aleurone of germinating c1 recessive kernels. The expression data show that sequences necessary for C1 gene activity are present in the vicinity of boxI and boxII.

Northern experiments with mRNA isolated from maturing (30 DAP) and germinating kernels support the results of the promoter analysis and indicate different modes of regulation of C1 and the structural genes C2 and A1 within the various alleles.

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