ALLELES OF THE MAIZE-P GENE WITH DISTINCT TISSUE SPECIFICITIES ENCODEMYB-HOMOLOGOUS PROTEINS WITH C-TERMINAL REPLACEMENTS

The maize P gene is a transcriptional regulator of genes encoding enzy mes for flavonoid biosynthesis in the pathway leading to the productio n of a red phlobaphene pigment. Multiple alleles of the P gene confer distinct patterns of pigmentation to specific floral organs, such as t he kernel pericarp and cob tissues, To determine the basis of allele-s pecific pigmentation, we have characterized the gene products and tran script accumulation patterns of the P wr allele, which specifies color less pericarps and red cob tissues. RNA transcripts of P-wr are presen t in colorless pericarps as well as in the colored cob tissues; howeve r, the expression of P wr in pericarp does not induce the accumulation of transcripts from the C2 and Al genes, which encode enzymes for fla vonoid pigment biosynthesis. The coding sequences of P-wr were compare d with the P rr allele, which specifies red pericarp and red cob, The P wr and P rr cDNA sequences are very similar in their 5' regions. The re are only two nucleotide changes that result in amino acid differenc es; both are outside of the Myb-homologous DNA binding domain. In cont rast, the 3' coding region of P rr is replaced by a unique 210-bp sequ ence in P-wr. The predicted P-wr protein has a C-terminal sequence res embling a cysteine-containing metal binding domain that is not present in the P-rr protein. These results indicate that the differential per icarp pigmentation specified by the P rr and P-wr alleles does not res ult from an absence of P wr transcripts in pericarps. Rather, the alle le-specific patterns of P rr and P wr pigmentation may be associated w ith structural differences in the proteins encoded by each allele.