The dominant inhibitory chalcone synthase allele C2-Idf (inhibitor diffuse) from Zea mays (L.) acts via an endogenous RNA silencing mechanism.
The flavonoid pigment pathway in plants has been used as a model system for studying gene regulatory mechanisms. C2-Idf is a stable dominant mutation of the chalcone synthase gene, c2, which encodes the first dedicated enzyme in this biosynthetic pathway of maize. Homozygous C2-Idf plants show no pigmentation. This allele also inhibits expression of functional C2 alleles in heterozygotes, producing a less pigmented condition instead of the normal deeply pigmented phenotype. To explore the nature of this effect, the C2-Idf allele was cloned. The gene structure of the C2-Idf haplotype differs substantially from that of the normal c2 gene in that three copies are present. Two of these are located in close proximity to each other in a head-to-head orientation and the third is closely linked. Previous experiments showed that the lower level of pigmentation in heterozygotes is correlated with reduced enzyme activity and low steady-state mRNA levels. We found that c2 transcription occurs in nuclei of C2-Idf/C2 heterozygotes, but mRNA does not accumulate, suggesting that the inhibition is mediated by RNA silencing. Infection of C2-Idf/C2 heterozygotes with viruses that carry suppressors of RNA silencing relieved the phenotypic inhibition, restoring pigment production and mRNA levels. Finally, we detected small interfering RNAs (siRNAs) in plants carrying C2-Idf, but not in plants homozygous for the wild-type C2 allele. Together, our results indicate that the inhibitory effect of C2-Idf occurs through RNA silencing.
Della Vedova
Chris B
CB
Genetics Area Program, University of Missouri, Columbia, Missouri 65211, USA.
Lorbiecke
René
R
Kirsch
Helene
H
Schulte
Michael B
MB
Scheets
Kay
K
Borchert
Lutz M
LM
Scheffler
Brian E
BE
Wienand
Udo
U
Cone
Karen C
KC
Birchler
James A
JA
D000217:Acyltransferases / Q000235:genetics*; D000483:Alleles; D002467:Cell Nucleus / Q000235:genetics; D003001:Cloning, Molecular; D019175:DNA Methylation; D018744:DNA, Plant / Q000032:analysis; D018628:Gene Dosage; D005799:Genes, Dominant; D017343:Genes, Plant; D018745:Genome, Plant; D006239:Haplotypes; D006579:Heterozygote; D006720:Homozygote; D008969:Molecular Sequence Data; D009154:Mutation; D011401:Promoter Regions, Genetic; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D034741:RNA, Small Interfering / Q000032:analysis; D017422:Sequence Analysis, DNA; D014158:Transcription, Genetic; D003313:Zea mays / Q000235:genetics*
D018744:DNA, Plant; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D000217:Acyltransferases; C020141:flavanone synthetase