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A New Approach for the Comparative Analysis of Multiprotein Complexes Based on 15N Metabolic Labeling and Quantitative Mass Spectrometry
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Stability determinants in the chloroplast psbB/T/H mRNAs of Chlamydomonas reinhardtii

F E Vaistij1, M Goldschmidt-Clermont, K Wostrikoff

  • 1Department of Molecular Biology,Department of Plant Biology, University of Geneva, Sciences II, 30 quai Ernest-Ansermet, CH-1211 Geneva 4, Switzerland.

The Plant Journal : for Cell and Molecular Biology
|April 12, 2000
PubMed

Insights

A nucleus-encoded factor, Mbb1, is essential for chloroplast gene expression and photosystem II assembly in Chlamydomonas reinhardtii. It specifically targets psbB mRNA, influencing its accumulation and stability.

Area of Science:

  • Chloroplast gene expression
  • Photosynthesis research
  • Molecular genetics

Background:

  • The psbB gene encodes CP47, a core subunit of photosystem II (PSII).
  • Nuclear mutant 222E lacks psbB, psbT, and psbH mRNA accumulation due to a mutation in the Mbb1 gene.
  • Mbb1 is a nucleus-encoded factor crucial for specific chloroplast gene expression.

Purpose of the Study:

  • To map the Mbb1 target site within the psbB 5' untranslated region (UTR).
  • To investigate the mechanisms regulating psbB mRNA stability and accumulation.
  • To understand the role of Mbb1 in chloroplast gene expression and PSII assembly.

Main Methods:

  • Introduction of chimeric psbB-aadA genes into chloroplasts.
  • Primer extension analysis of psbB RNA.
  • Deletion analysis of putative stem-loop structures in the 5' UTR.
  • Insertion of a poly G cassette to assess transcript stability.

Main Results:

  • The Mbb1 target site was mapped to the psbB 5' UTR.
  • Two psbB mRNA forms were identified: a long form (less abundant) and a short form (more abundant).
  • The short form accumulates only in wild-type, suggesting Mbb1's role in its processing or stability.
  • A 5'-3' exonuclease may be involved in psbB mRNA regulation.
  • psbH and psbT are co-transcribed with psbB, and psbH mRNA also has an Mbb1 target site.

Conclusions:

  • Mbb1 is essential for the accumulation of the mature, short form of psbB mRNA.
  • Mbb1 likely regulates chloroplast gene expression post-transcriptionally, possibly involving mRNA degradation pathways.
  • This nucleus-encoded factor plays a critical role in coordinating chloroplast gene expression for the proper assembly of the photosystem II complex.

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