Submitted to: Plant Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/28/2001
Publication Date: 9/1/2001
Citation: COCCIOLONE, S.M., CHOPRA, S., FLINT-GARCIA, S.A., MCMULLEN, M.D., PETERSON, T. TISSUE-SPECIFIC PATTERNS OF A MAIZE MYB TRANSCRIPTION FACTOR ARE EPIGENETICALLY REGULATED. PLANT JOURNAL. 2001. V. 27(5). P. 467-478. Interpretive Summary: One of the major limiting factors in crop improvement through transformation is the variability of expression of the introduced gene in different transformation events and the instability of expression of many introduced genes. In this study, the molecular and genetic basis of tissue- specific expression of the p1 gene, a regulator of pericarp and cob color in maize, was studied. What was found was that the origin or DNA sequence of the introduced gene did not determine tissue-specific expression, rather tissue-specific expression was controlled after the gene is introduced. DNA methylation was correlated to tissue specificity and level of gene expression in different transformation events. The impact of this study demonstrates the importance of so called "epigenetic" control of gene expression in transformation experiments giving an explanation to many of the transformation results obtained to date. This study benefits scientists conducting transformation experiments by providing testable hypotheses to examine the basis of variable expression of introduced genes.
Technical Abstract: The maize p1 gene encodes a Myb-homologous regulator of red pigment biosynthesis. To investigate the tissue-specific regulation of P1-wr, a white pericarp and red cob allele, maize plants were transformed with constructs combining promoter and cDNA sequences of P1-wr and P1-rr, a red pericarp and red cob allele. Surprisingly, all promoter/cDNA combinations produced transgenic plants with red pericarp and red cob (RR pattern), including a P1-wr promoter driving a P1-wr cDNA. The P1-wr phenotype (WR pattern) was only observed when RR patterned plants from two independent transgenic lines spontaneously produced progeny plants with the WR pattern. This switch in tissue-specific expression correlated with an increase in transgene methylation. A similar association between presence or absence of pericarp pigmentation and degree of DNA methylation was observed for certain natural p1 alleles. p1 alleles were identified that had the gene structure characteristic of standard P1-wr alleles; however, these alleles conferred red pericarp pigmentation and were consistently less methylated than standard P1-wr alleles. Taken together, our results provide evidence that tissue-specific regulation of the P1-wr phenotype is epigenetically controlled.