Alleles of the maize P gene with distinct tissue specificities encode Myb-homologous proteins with C-terminal replacements.
The maize P gene is a transcriptional regulator of genes encoding enzymes for flavonoid biosynthesis in the pathway leading to the production of a red phlobaphene pigment. Multiple alleles of the P gene confer distinct patterns of pigmentation to specific floral organs, such as the kernel pericarp and cob tissues. To determine the basis of allele-specific pigmentation, we have characterized the gene products and transcript accumulation patterns of the P-wr allele, which specifies colorless pericarps and red cob tissues. RNA transcripts of P-wr are present in colorless pericarps as well as in the colored cob tissues; however, the expression of P-wr in pericarp does not induce the accumulation of transcripts from the C2 and A1 genes, which encode enzymes for flavonoid pigment biosynthesis. The coding sequences of P-wr were compared 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. There are only two nucleotide changes that result in amino acid differences; both are outside of the Myb-homologous DNA binding domain. In contrast, the 3' coding region of P-rr is replaced by a unique 210-bp sequence in P-wr. The predicted P-wr protein has a C-terminal sequence resembling a cysteine-containing metal binding domain that is not present in the P-rr protein. These results indicate that the differential pericarp pigmentation specified by the P-rr and P-wr alleles does not result from an absence of P-wr transcripts in pericarps. Rather, the allele-specific patterns of P-rr and P-wr pigmentation may be associated with structural differences in the proteins encoded by each allele.
Chopra
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S
Department of Zoology and Genetics, Iowa State University, Ames 50011, USA.
Athma
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P
Peterson
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T
D000483:Alleles; D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D017931:DNA Primers; D004268:DNA-Binding Proteins / Q000096:biosynthesis* / Q000235:genetics*; D005419:Flavonoids / Q000096:biosynthesis; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D015321:Gene Rearrangement; D017343:Genes, Plant; D008969:Molecular Sequence Data; D009928:Organ Specificity; D010940:Plant Proteins / Q000096:biosynthesis* / Q000235:genetics*; D016133:Polymerase Chain Reaction; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D020598:Proto-Oncogene Proteins c-myb; D017386:Sequence Homology, Amino Acid; D015534:Trans-Activators / Q000235:genetics*; D014158:Transcription, Genetic; D003313:Zea mays / Q000235:genetics*
D017931:DNA Primers; D004268:DNA-Binding Proteins; D005419:Flavonoids; C085863:P protein, Zea mays; D010940:Plant Proteins; D011518:Proto-Oncogene Proteins; D020598:Proto-Oncogene Proteins c-myb; D015534:Trans-Activators