The dynamin-like protein Fzl promotes thylakoid fusion and resistance to light stress in <i>Chlamydomonas reinhardtii</i> - Fig 6

(a-c) Top schemes. Representation of a wild-type (a), a ΔPSI (b) and a ΔPSII (c) cell in regard to the synthesis of the subunits of interest. In a wild-type strain (a), PSI subunit is encoded by the psaB gene on the chloroplast genome. mRNA translation is allowed by the nuclear encoded factor TAB1. PsaB is then inserted in thylakoid membranes as part of the PSI. On the other hand, the PSII subunit PsbC is also encoded on the chloroplast genome and will be translated before insertion in the PSII. In the ΔPSI mutant F15 (b), the translation factor TAB1 is missing, preventing translation of the PsaB subunit and assembly of PSI. In the ΔPSII strain Fud34 (c), a mutation in the 5’UTR of the psbC mRNA induces the formation of a secondary structure that prevents its translation and assembly of the PSII. Bottom graphs. Chlorophyll fluorescence induction kinetic of the corresponding strains. (d) Top scheme. Representation of a zygote from a ΔPSI x ΔPSII cross in presence of chloramphenicol (CAP) and after thylakoid fusion. CAP prevents translation of both plastid encoded photosystem subunits PsaB and PsbC, and therefore the de novo assembly and insertion of functional PSI and PSII in parental thylakoid membranes. Pre-existing PSI and PSII complexes are mixed following fusion of the thylakoid membranes. Note that during mating, chloroplast DNA of the mt- parental strain is degraded. Bottom graph. Chlorophyll fluorescence induction kinetic of the zygote with fused thylakoid showing recovery of photosynthetic electron transfer witnessed by fluorescence relaxation as in (a).. (e) Top scheme. Representation of a zygote with non-fused thylakoids. Bottom graph. Chlorophyll fluorescence induction kinetic of ΔPSI and ΔPSII cells mixed in equal amount to mimic a lack of thylakoid fusion. (f) Chlorophyll fluorescence induction kinetics from zygotes in the different crosses performed in the absence or in the presence of CAP.