The Elm1 (ZmHy2) gene of maize encodes a phytochromobilin synthase.

Ruairidh J.H. Sawers, Philip J. Linley, Jose F. Gutierrez-Marcos, Teegan Delli-Bovi, Phyllis R. Farmer, Takayuki Kohchi, Matthew J. Terry, Thomas P. Brutnell

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Abstract

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.

Original languageEnglish (US)
Pages (from-to)2771-2781
Number of pages11
JournalPlant physiology
Volume136
Issue number1
DOIs
StatePublished - Sep 2004

All Science Journal Classification (ASJC) codes

  • Physiology
  • Genetics
  • Plant Science

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