Evidence fromIn vivoManipulations of Lipid Composition in Mutants that the Δ3‐Trans‐Hexadecenoic Acid‐Containing Phosphatidylglycerol is Involved in the Biogenesis of the Light‐Harvesting Chlorophylla/b‐Protein Complex ofChlamydomonas reinhardtii

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Abstract
The phosphatidylglycerol containing the unusual Δ3‐transhexadecenoic fatty acid is specifically found in photosynthetic membranes of eukaryotic organisms. Its involvement in the biogenesis and the structure of the light‐harvesting chlorophylla/b‐protein complex has been evidenced byin vivotargeting this lipid to photosynthetic membranes ofChlamydomonas reinhardtiimutants lacking this lipid. In themf1andmf2mutants, this deficiency results in (a) the absence of the oligomeric lightharvesting complex of photosystem 2; (b) an extensive destacking of thylakoid membranes; (c) a very low 77‐K fluorescence emission in the photosystem–2 region.We show in this paper that these deficiencies result from modifications in the pigment and polypeptide compositions of the photosystem‐2 light‐harvesting complex; it contains less chlorophyllband some of its constitutive polypeptides are absent or reduced in amount, while immunologically related polypeptides of lower molecular mass accumulate. The direct involvement of the lack oftrans‐C16: 1‐phosphatidylglycerol in these deficiencies is evidenced by the partial restoration of normal characteristics of the light–harvesting complex (pigment and polypeptide composition, oligomerization) after liposome‐mediated,in vivoincorporation of this lipid into the photosynthetic membranes of themflmutant.Trans‐C16: 1‐phosphatidylglycerol, therefore, is involved in the biogenesis of the photosystem‐2 light‐harvesting chlorophylla/b‐protein complex through a mechanism that may prevent degradation processes. Its contribution to the structural conformation of neosynthesized monomers and to their organization into stable oligomeric form is discussed.