White Mutants of Chlamydomonas reinhardtii Are Defective in Phytoene SynthaseSequence data from this article have been deposited with the EMBL/GenBank Data Libraries under accession nos. AY604700, PSY (137c) cDNA; AY604701, PSY (137c) genomic DNA; AY604702, PSY (S1D2) genomic DNA; and AY604703, PDS (137c) cDNA.

Abstract

Carotenoids play an integral and essential role in photosynthesis and photoprotection in plants and algae. A collection of Chlamydomonas reinhardtii mutants lacking carotenoids was characterized for pigment and tocopherol (vitamin E) composition, growth phenotypes under different light conditions, and the molecular basis of their mutant phenotype. The carotenoid-less mutants, or "white" mutants, were also deficient in chlorophylls but had approximately twice the tocopherol content of the wild type. White mutants grew in the dark but were unable to survive in the light, even under very low light conditions on acetate-containing medium. Genetic crosses and recombination tests revealed that all individual white mutants in the collection are alleles of a single gene, lts1, and the white phenotype was closely linked to a marker located in the phytoene synthase gene. DNA sequencing of the phytoene synthase gene from each of the mutants revealed nonsense, missense, frameshift, and splice site mutations. Transformation with a wild-type copy of the phytoene synthase gene was able to complement the lts1-210 mutation. Together, these results show that all the white mutants examined in this work are affected in the phytoene synthase gene.

Most microRNAs in the single-cell alga Chlamydomonas reinhardtii are produced by Dicer-like 3-mediated cleavage of introns and untranslated regions of coding RNAs

“…1B) most likely due to silencing of PSY mRNA by the amiRNA and to the consequent lack of the photoprotective function of PSY (McCarthy et al 2004). Consistent with this interpretation the cell death was dependent on the light intensity (Supplemental Fig.…”

Overlapping Photoprotective Function of Vitamin E and Carotenoids inChlamydomonas

“…For example, geranylgeranyl pyrophosphate is a common substrate for the carotenoid and tocopherol biosynthetic pathways. Mutation of phytoene synthase in C. reinhardtii results in increased levels of a-tocopherol, possibly due to an increased availability of geranylgeranyl pyrophosphate for tocopherol biosynthesis (McCarthy et al, 2004). Since the prenylation steps of the tocopherol and plastoquinone biosynthesis pathways require the same aromatic head group, homogentisic acid, it is conceivable that VTE2 overexpression might affect plastoquinone biosynthesis.…”

Replacement of α-Tocopherol by β-Tocopherol Enhances Resistance to Photooxidative Stress in a Xanthophyll-Deficient Strain of Chlamydomonas reinhardtii

“…Vector pMS188, carrying a zeocin resistance gene, was cotransformed to select for transformants (45). Nuclear transformation was carried out as previously described (30). The amounts of vector pGenD-Ble and vector pMS188 used were 1 g and 300 ng, respectively.…”