Development of the light-harvesting chlorophyll antenna in the green alga Chlamydomonas reinhardtii is regulated by the novel Tla1 gene

The Chlamydomonas reinhardtii tla1 (truncated light-harvesting chlorophyll antenna size) mutant was generated upon DNA insertional mutagenesis and shown to specifically possess a smaller than wild type (WT) chlorophyll antenna size in both photosystems. Molecular and genetic analysis revealed that the exogenous plasmid DNA was inserted at the end of the 5' UTR and just prior to the ATG start codon of a hitherto unknown nuclear gene (termed Tla1), which encodes a protein of 213 amino acids. The Tla1 gene in the mutant is transcribed with a new 5' UTR sequence, derived from the 3' end of the transforming plasmid. This replacement of the native 5' UTR and promoter regions resulted in enhanced transcription of the tla1 gene in the mutant but inhibition in the translation of the respective tla1 mRNA. Transformation of the tla1 mutant with WT Tla1 genomic DNA successfully rescued the mutant. These results are evidence that polymorphism in the 5' UTR of the Tla1 transcripts resulted in the tla1 phenotype and that expression of the Tla1 gene is a prerequisite for the development/assembly of the Chl antenna in C. reinhardtii. A blast search with the Tla1 deduced amino acid sequence revealed that this protein is highly conserved in many eukaryotes. It showed homology to a protein of unknown function in Arabidopsis thaliana (73%), Oryza sativa (76%), Drosophila melanogaster (71%) and Homo sapiens (67%). The Tla1 gene apparently regulates genes that define the Chl antenna size in the photosynthetic apparatus of C. reinhardtii. Potential applications of the Tla1 gene in photosynthesis and biotechnology are discussed.