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In vivo evidence for a regulatory role of phosphorylation of Arabidopsis Rubisco activase at the Thr78 site

Kim, SY and Harvey, CM and Giese, J and Lassowskat, I and Singh, V and Cavanagh, AP and Spalding, MH and Finkemeier, I and Ort, DR and Huber, SC (2019) 'In vivo evidence for a regulatory role of phosphorylation of Arabidopsis Rubisco activase at the Thr78 site.' Proceedings of the National Academy of Sciences of the United States of America, 116 (37). 18723 - 18731. ISSN 0027-8424

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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 (ΦPSII) and reduced growth relative to control plants expressing wildtype 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 ΦPSII 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 rcaknockdown 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.

Item Type: Article
Divisions: Faculty of Science and Health > Life Sciences, School of
Depositing User: Elements
Date Deposited: 11 Jan 2021 12:27
Last Modified: 16 Nov 2021 08:15
URI: http://repository.essex.ac.uk/id/eprint/28714

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