Maize plastid gene expressed during photoregulated development.

Area of Science:

• Plant Molecular Biology
• Chloroplast Development
• Gene Expression Analysis

Background:

• Etioplasts in dark-grown maize seedlings lack chlorophyll and organized internal structures.
• Light exposure triggers etioplasts to develop into photosynthetically active chloroplasts.
• Understanding the molecular mechanisms of this light-induced transformation is crucial for plant biology.

Purpose of the Study:

• To identify and characterize specific RNAs involved in maize plastid development.
• To investigate the photoregulated expression of genes during the transition from etioplasts to chloroplasts.
• To map the location of key RNA transcripts on the maize chloroplast DNA.

Main Methods:

• Isolation and in vitro labeling of RNAs from etioplasts and developing plastids.
• Hybridization of labeled RNAs to endonuclease-digested maize chloroplast DNA fragments.
• In vitro translation of plastid RNAs using a rabbit reticulocyte system.
• Mapping of RNA hybridization sites on the plastid chromosome.

Main Results:

• A major nonribosomal RNA, undetectable in etioplasts but present in developing plastids, hybridizes to Bam fragment 8 of maize chloroplast DNA.
• This RNA has been mapped to a specific location on the maize plastid chromosome.
• Developing plastids and mature chloroplasts, but not etioplasts, contain mRNA encoding a ~34,500 dalton polypeptide.
• The RNA hybridizing to Bam 8 and the mRNA for the 34,500 dalton protein appear simultaneously during light-induced development.

Conclusions:

• The simultaneous appearance of the Bam 8-hybridizing RNA and the translatable mRNA suggests they originate from the same gene.
• This indicates the photoregulated expression of a single gene during light-induced maize plastid development.
• The study identifies a key molecular event in the transition of etioplasts to chloroplasts.