M-Type Thioredoxins Regulate the PGR5/PGRL1-Dependent Pathway by Forming a Disulfide-Linked Complex with PGRL1

Plant Cell. 2020 Dec;32(12):3866-3883. doi: 10.1105/tpc.20.00304. Epub 2020 Oct 9.

Abstract

In addition to linear electron transport, photosystem I cyclic electron transport (PSI-CET) contributes to photosynthesis and photoprotection. In Arabidopsis (Arabidopsis thaliana), PSI-CET consists of two partially redundant pathways, one of which is the PROTON GRADIENT REGULATION5 (PGR5)/PGR5-LIKE PHOTOSYNTHETIC PHENOTYPE1 (PGRL1)-dependent pathway. Although the physiological significance of PSI-CET is widely recognized, the regulatory mechanism behind these pathways remains largely unknown. Here, we report on the regulation of the PGR5/PGRL1-dependent pathway by the m-type thioredoxins (Trx m). Genetic and phenotypic characterizations of multiple mutants indicated the physiological interaction between Trx m and the PGR5/PGRL1-dependent pathway in vivo. Using purified Trx proteins and ruptured chloroplasts, in vitro, we showed that the reduced form of Trx m specifically decreased the PGR5/PGRL1-dependent plastoquinone reduction. In planta, Trx m4 directly interacted with PGRL1 via disulfide complex formation. Analysis of the transgenic plants expressing PGRL1 Cys variants demonstrated that Cys-123 of PGRL1 is required for Trx m4-PGRL1 complex formation. Furthermore, the Trx m4-PGRL1 complex was transiently dissociated during the induction of photosynthesis. We propose that Trx m directly regulates the PGR5/PGRL1-dependent pathway by complex formation with PGRL1.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arabidopsis / genetics*
  • Arabidopsis / physiology
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism*
  • Chloroplast Thioredoxins / genetics
  • Chloroplast Thioredoxins / metabolism*
  • Chloroplasts / metabolism
  • Disulfides / metabolism
  • Electron Transport
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism*
  • Photosynthesis
  • Photosynthetic Reaction Center Complex Proteins / genetics
  • Photosynthetic Reaction Center Complex Proteins / metabolism*
  • Photosystem I Protein Complex / metabolism
  • Plants, Genetically Modified
  • Plastoquinone / metabolism*

Substances

  • Arabidopsis Proteins
  • Chloroplast Thioredoxins
  • Disulfides
  • Membrane Proteins
  • PGR5 protein, Arabidopsis
  • PGRL1 protein, Arabidopsis
  • Photosynthetic Reaction Center Complex Proteins
  • Photosystem I Protein Complex
  • TRX m4 protein, Arabidopsis
  • Plastoquinone