Abstract
Arabidopsis Rubisco activase (Rca) is phosphorylated at threonine-78 (Thr78) in low light and in the dark, suggesting a potential regulatory role in photosynthesis, but this has not been directly tested. To do so, we transformed an rca -knockdown mutant largely lacking redox regulation with wild-type Rca-β or Rca-β with Thr78-to-Ala (T78A) or Thr78-to-Ser (T78S) site–directed mutations. Interestingly, the T78S mutant was hyperphosphorylated at the Ser78 site relative to Thr78 of the Rca-β wild-type control, as evidenced by immunoblotting with custom antibodies and quantitative mass spectrometry. Moreover, plants expressing the T78S mutation had reduced photosynthesis and quantum efficiency of photosystem II (ϕ PSII ) and reduced growth relative to control plants expressing wild-type Rca-β under all conditions tested. Gene expression was also altered in a manner consistent with reduced growth. In contrast, plants expressing Rca-β with the phospho-null T78A mutation had faster photosynthetic induction kinetics and increased ϕ PSII relative to Rca-β controls. While expression of the wild-type Rca-β or the T78A mutant fully rescued the slow-growth phenotype of the rca- knockdown mutant grown in a square-wave light regime, the T78A mutants grew faster than the Rca-β control plants at low light (30 µmol photons m −2 s −1 ) and in a fluctuating low-light/high-light environment. Collectively, these results suggest that phosphorylation of Thr78 (or Ser78 in the T78S mutant) plays a negative regulatory role in vivo and provides an explanation for the absence of Ser at position 78 in terrestrial plant species.
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Claims 11
Claim · model-written summary
T78S Rca was hyperphosphorylated at Ser78 relative to wild-type Thr78.
- Taxon
- Arabidopsis
Arabidopsist0 - Material
- T78S mutante0
- Gene
- Rca-βe0
- Outcome
- phosphorylatede0
- Direction
- hyperphosphorylatede0
- Comparator
- Rca-β wild-type controle0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the T78S mutant was hyperphosphorylated at the Ser78 site relative to Thr78 of the Rca-β wild-type control”
t0“Arabidopsis”
Claim · model-written summary
T78S plants had reduced photosynthesis and photosystem II quantum efficiency relative to wild-type Rca-β controls.
- Taxon
- ArabidopsisArabidopsist0
- Treatment
- T78S mutatione0
- Outcome
- photosynthesis and quantum efficiency of photosystem II (ϕ PSII )e0
- Direction
- reducede0
- Comparator
- control plants expressing wild-type Rca-βe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“plants expressing the T78S mutation had reduced photosynthesis and quantum efficiency of photosystem II (ϕ PSII ) and reduced growth relative to control plants expressing wild-type Rca-β under all conditions tested”
t0“Arabidopsis”
Claim · model-written summary
T78S plants grew less than controls under all tested conditions.
- Taxon
- ArabidopsisArabidopsist0
- Treatment
- T78S mutatione0
- Outcome
- growthe0
- Direction
- reducede0
- Comparator
- control plants expressing wild-type Rca-βe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“plants expressing the T78S mutation had reduced photosynthesis and quantum efficiency of photosystem II (ϕ PSII ) and reduced growth relative to control plants expressing wild-type Rca-β under all conditions tested”
t0“Arabidopsis”
Claim · model-written summary
Gene expression in T78S plants changed consistently with reduced growth.
- Taxon
- ArabidopsisArabidopsist0
- Outcome
- Gene expressione0
- Direction
- alterede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Gene expression was also altered in a manner consistent with reduced growth”
t0“Arabidopsis”
Claim · model-written summary
T78A plants had faster photosynthetic induction kinetics than Rca-β controls.
- Taxon
- ArabidopsisArabidopsist0
- Treatment
- phospho-null T78A mutatione0
- Outcome
- photosynthetic induction kineticse0
- Direction
- fastere0
- Comparator
- Rca-β controlse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“plants expressing Rca-β with the phospho-null T78A mutation had faster photosynthetic induction kinetics and increased ϕ PSII relative to Rca-β controls”
t0“Arabidopsis”
Claim · model-written summary
T78A plants had increased photosystem II quantum efficiency compared with Rca-β controls.
- Taxon
- ArabidopsisArabidopsist0
- Treatment
- phospho-null T78A mutatione0
- Outcome
- ϕ PSIIe0
- Direction
- increasede0
- Comparator
- Rca-β controlse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“plants expressing Rca-β with the phospho-null T78A mutation had faster photosynthetic induction kinetics and increased ϕ PSII relative to Rca-β controls”
t0“Arabidopsis”
Claim · model-written summary
Wild-type Rca-β fully rescued slow growth in the rca knockdown under square-wave light.
- Taxon
- ArabidopsisArabidopsist0
- Treatment
- wild-type Rca-βe0
- Outcome
- slow-growth phenotypee0
- Direction
- rescuede0
- Comparator
- rca- knockdown mutante0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“expression of the wild-type Rca-β or the T78A mutant fully rescued the slow-growth phenotype of the rca- knockdown mutant grown in a square-wave light regime”
t0“Arabidopsis”
Claim · model-written summary
T78A fully rescued slow growth in the rca knockdown under square-wave light.
- Taxon
- ArabidopsisArabidopsist0
- Treatment
- T78A mutante0
- Outcome
- slow-growth phenotypee0
- Direction
- rescuede0
- Comparator
- rca- knockdown mutante0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“expression of the wild-type Rca-β or the T78A mutant fully rescued the slow-growth phenotype of the rca- knockdown mutant grown in a square-wave light regime”
t0“Arabidopsis”
Claim · model-written summary
T78A grew faster than Rca-β controls under low light.
- Taxon
- ArabidopsisArabidopsist0
- Treatment
- T78A mutantse0
- Outcome
- grewe0
- Direction
- fastere0
- Qualifier
- low light (30 µmol photons m −2 s −1 )e0
- Comparator
- Rca-β control plantse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the T78A mutants grew faster than the Rca-β control plants at low light (30 µmol photons m −2 s −1 )”
t0“Arabidopsis”
Claim · model-written summary
T78A grew faster than Rca-β controls in fluctuating low and high light.
- Taxon
- ArabidopsisArabidopsist0
- Treatment
- T78A mutantse0
- Outcome
- grewe0
- Direction
- fastere0
- Qualifier
- fluctuating low-light/high-light environmente0
- Comparator
- Rca-β control plantse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the T78A mutants grew faster than the Rca-β control plants at low light (30 µmol photons m −2 s −1 ) and in a fluctuating low-light/high-light environment”
t0“Arabidopsis”
Claim · model-written summary
Thr78 phosphorylation is proposed to negatively regulate Rca in vivo.
- Taxon
- ArabidopsisArabidopsist0
- Gene
- Thr78e0
- Outcome
- negative regulatory role in vivoe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“phosphorylation of Thr78 (or Ser78 in the T78S mutant) plays a negative regulatory role in vivo”
t0“Arabidopsis”
The same questions in other papers
loss of function · physiology: photosynthesis · ArabidopsisPositive and negative results
5 papers in the same direction as this paper · 15 in the opposite direction
- negative
- negative
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17 papers more in this group
See all 21 papers →Claims are grouped by organism, treatment and what was measured or targeted. A paper counts as positive when any of its claims in the group is positive.