Piotr Stepien and Giles N. Johnson

PNAS September 18, 2018 115 (38) 9634-9639

Significance

Growing concerns about food security and changing climates make the identification of stress-tolerance traits a priority. Here we show that the activation of the plastid terminal oxidase, via its relocation within the thylakoid membrane, can induce a protective sink for electron transport. We have thus identified an unexpected mechanism for protein activation and opened avenues for engineering plant stress tolerance.

Abstract

The plastid terminal oxidase (PTOX) has been shown to be an important sink for photosynthetic electron transport in stress-tolerant plants. However, overexpression studies in stress-sensitive species have previously failed to induce significant activity of this protein. Here we show that overexpression of PTOX from the salt-tolerant brassica species Eutrema salsugineum does not, alone, result in activity, but that overexpressing plants show faster induction and a greater final level of PTOX activity once exposed to salt stress. This implies that an additional activation step is required before activity is induced. We show that that activation involves the translocation of the protein from the unstacked stromal lamellae to the thylakoid grana and a protection of the protein from trypsin digestion. This represents an important activation step and opens up possibilities in the search for stress-tolerant crops.

See: http://www.pnas.org/content/115/38/9634

Figure 1: Chlorophyll fluorescence parameters in the leaves of Arabidopsis thaliana (A and C) and Eutrema salsugineum (Band D) exposed to: 0 (squares) and either 150 (Arabidopsis) or 250 (Eutrema) mM NaCl (circles) for periods of up to 14 d. Salt treatments were started on day 0. Wild types are denoted by solid lines, and At-OE8 and Es-OE6 are denoted by dotted lines. Measurements were performed in the presence of 385 μL L⁻¹ CO₂, actinic light (PFD 850 μmol m⁻² s⁻¹). The photochemical efficiency of PSII (A and B) and NPQ (C and D) was calculated. Data points represent the means ± SE of at least six biological replicates.