The Elm1 (ZmHy2) gene of maize encodes a phytochromobilin synthase.
The light insensitive maize (Zea mays) mutant elongated mesocotyl1 (elm1) has previously been shown to be deficient in the synthesis of the phytochrome chromophore 3E-phytochromobilin (PPhiB). To identify the Elm1 gene, a maize homolog of the Arabidopsis PPhiB synthase gene AtHY2 was isolated and designated ZmHy2. ZmHy2 encodes a 297-amino acid protein of 34 kD that is 50% identical to AtHY2. ZmHY2 was predicted to be plastid localized and was targeted to chloroplasts following transient expression in tobacco (Nicotiana plumbaginifolia) leaves. Molecular mapping indicated that ZmHy2 is a single copy gene in maize that is genetically linked to the Elm1 locus. Sequence analysis revealed that the ZmHy2 gene of elm1 mutants contains a single G to A transition at the 3' splice junction of intron III resulting in missplicing and premature translational termination. However, flexibility in the splicing machinery allowed a small pool of in-frame ZmHy2 transcripts to accumulate in elm1 plants. In addition, multiple ZmHy2 transcript forms accumulated in both wild-type and elm1 mutant plants. ZmHy2 splice variants were expressed in Escherichia coli and products examined for activity using a coupled apophytochrome assembly assay. Only full-length ZmHY2 (as defined by homology to AtHY2) was found to exhibit PPhiB synthase activity. Thus, the elm1 mutant of maize is deficient in phytochrome response due to a lesion in a gene encoding phytochromobilin synthase that severely compromises the PPhiB pool.
Sawers
Ruairidh J H
RJ
Boyce Thompson Institute, Cornell University, Ithaca, NY 14853, USA.
Linley
Philip J
PJ
Gutierrez-Marcos
Jose F
JF
Delli-Bovi
Teegan
T
Farmer
Phyllis R
PR
Kohchi
Takayuki
T
Terry
Matthew J
MJ
Brutnell
Thomas P
TP
D000595:Amino Acid Sequence; D001483:Base Sequence; D018744:DNA, Plant / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics; D017343:Genes, Plant; D008040:Genetic Linkage; D008969:Molecular Sequence Data; D009154:Mutation; D010088:Oxidoreductases / Q000235:genetics* / Q000378:metabolism; D018087:Plastids / Q000201:enzymology; D012326:RNA Splicing; D018749:RNA, Plant / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D003313:Zea mays / Q000201:enzymology* / Q000235:genetics*
D018744:DNA, Plant; D018749:RNA, Plant; D011994:Recombinant Proteins; D010088:Oxidoreductases; C071703:phytochromobilin synthase