Nuclear Suppressors of the Photosensitivity Associated with Defective Photosynthesis in <i>Chlamydomonas reinhardii</i>

Spreitzer, Robert J.; Ogren, William L.

doi:10.1104/pp.71.1.35

Cited by 19 publications

(8 citation statements)

References 10 publications

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“…This recovery frequency for acetate-requiring mutants is about 7 times greater than that reported for previous insertionalmutagenesis experiments performed in the light (37). It is well known that C. reinhardtii photosynthesis-deficient mutants can be killed or selected against on acetate medium in the light (25,40). About 80% of our acetate-requiring insertional mutants were light-sensitive, and could be maintained only in darkness.…”

Section: Resultsmentioning

confidence: 61%

Elimination of the Chlamydomonas gene family that encodes the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase

Khrebtukova

Spreitzer

1996

Proc. Natl. Acad. Sci. U.S.A.

108

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Ribulose-1,5-bisphosphate carboxylase͞ oxygenase (EC 4.1.1.39) is the key photosynthetic enzyme that catalyzes the first step of CO 2 fixation. The chloroplastlocalized holoenzyme of plants and green algae contains eight nuclear-encoded small subunits and eight chloroplastencoded large subunits. Although much has been learned about the enzyme active site that resides within each large subunit, it has been difficult to assess the role of eukaryotic small subunits in holoenzyme function and expression. Small subunits are coded by a family of genes, precluding genetic screening or nuclear transformation approaches for the recovery of small-subunit mutants. In this study, the two small-subunit genes of the green alga Chlamydomonas reinhardtii were eliminated during random insertional mutagenesis. The photosynthesis-deficient deletion mutant can be complemented with either of the two wild-type small-subunit genes or with a chimeric gene that contains features of both. Thus, either small subunit is sufficient for holoenzyme assembly and function. In the absence of small subunits, expression of chloroplast-encoded large subunits appears to be inhibited at the level of translation.

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Section: Resultsmentioning

confidence: 61%

Elimination of the Chlamydomonas gene family that encodes the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase

Khrebtukova

Spreitzer

1996

Proc. Natl. Acad. Sci. U.S.A.

108

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“…5); no ROS production, wild typelike growth and a high U PSII . A possible explanation is that during the transformation process these strains have accumulated alterations to other alternative pathways which would alleviate PSI acceptor side limitations, interestingly, such mutations which suppress light sensitivity have been reported to accumulate at high frequency in RuBisCO mutants (Spreitzer and Ogren 1983). An increased malate shunt, the pathway by which NADPH reducing equivalents are transferred to mitochondria to produce ATP, or an overexpression of plastid terminal oxidase, leading to the reoxidation of plastoquinols producing ATP and proton gradient by an alternative water-water cycle, would both increase the photosynthetic yield of the cell.…”

Section: Discussionmentioning

confidence: 98%

Manipulating RuBisCO accumulation in the green alga, Chlamydomonas reinhardtii

Johnson

2011

Plant Mol Biol

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The nuclear factor, Maturation/stability of RbcL (MRL1), regulates the accumulation of the chloroplast rbcL gene transcript in Chlamydomonas reinhardtii by stabilising the mRNA via its 5' UTR. An absence of MRL1 in algal mrl1 mutants leads to a complete absence of RuBisCO large subunit protein and thus a lack of accumulation of the RuBisCO holoenzyme. By complementing mrl1 mutants by random transformation of the nuclear genome with the MRL1 cDNA, different levels of rbcL transcript accumulate. We also observe that RuBisCO Large Subunit accumulation is perturbed. Complemented strains accumulating as little as 15% RuBisCO protein can grow phototrophically while RuBisCO in this range is limiting for phototrophic growth. We also observe that photosynthetic activity, here measured by the quantum yield of PSII, appears to be a determinant for phototrophic growth. In some strains that accumulate less RuBisCO, a strong production of reactive oxygen species is detected. In the absence of RuBisCO, oxygen possibly acts as the PSI terminal electron acceptor. These results show that random transformation of MRL1 into mrl1 mutants can change RuBisCO accumulation allowing a range of phototrophic growth phenotypes. Furthermore, this technique allows for the isolation of strains with low RuBisCO, within the range of acceptable photosynthetic growth and reasonably low ROS production. MRL1 is thus a potential tool for applications to divert electrons away from photosynthetic carbon metabolism towards alternative pathways.

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“…Furthermore, treatment of C. reinhardtii with 5-fluorodeoxyuridine decreases the genome ploidy of its sin gle chloroplast (103), which allows the recovery of photosynthesis-deficient chloroplast mutations (84,90). Following 5-fluorodeoxyuridine treatment and methylmethane sulfonate mutagenesis, and taking into account that photosyn thesis-deficient mutants are sensitive to light (90,91), acetate-requiring mu tants are recovered at frequencies greater than 1 x 10-3 when dark-grown colonies are screened by replica plating (84,90). About 65% of these acetate requiring mutants have clear deficiencies in photosynthetic processes (84,90).…”

Section: Screening For Mutationsmentioning

confidence: 99%