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Scientific result | Photosynthesis

Identification of a mechanism potentially involved in drought resistance in plants

​I2BC researchers identify drought-resistant mutants of the model plant Arabidopsis thaliana. These mutants, deficient in the expression of genes relatively far from those usually solicited in the response to drought, are no longer able to carry out the state transition, a process that enables plants to adjust the absorption of light by their two photosystems in an optimal way. They could constitute a way of improving crop resistance to drought.

Published on 7 December 2023

​Research into drought-resistant plants is necessary to meet the challenges of rising temperatures and predicted climate change. New characteristics need to be identified and methods developed to maintain and improve crop productivity under difficult environmental conditions.

In plants, there are two photosystems: photosystem 1 (PSI) and photosystem 2 (PSII), which carry out the photochemical reactions of photosynthesis in the chloroplast. The "state transition" phenomenon is based on the phosphorylation and acetylation of an amino acid (lysine) in an energy-collecting chlorophyll-protein complex associated with the photosystems. This complex, located at PSII in the dephosphorylated state and at PSI in the phosphorylated state, enables plants to adjust the absorption of their photosystems so as to maintain optimum performance when external conditions change.

In the present work, the authors have studied drought resistance in the model plant Arabidopsis thaliana, using state-transition mutants: an already well-characterized kinase mutant (enzyme catalyzing a phosphorylation reaction) (stn7) and other, less well-known enzyme mutants (chloroplast acetyltransferase) (nsi1 and nsi2). They hypothesized that a higher reduction state of the plastoquinone (PQ) pool, an event that occurs in the absence of a state transition, and the concomitant generation of singlet oxygen (1O2, an excited state of the O2 molecule) lead to tolerance to drought-induced stress. The researchers showed that the mutant seedlings showed improved main root growth and more lateral root formation. They were also able to show, using chlorophyll fluorescence measurements, that these mutants indeed had a more reduced PQ pool and produced more 1O2. A pharmacological approach on wild-type seedlings, in which more reduced PQ pools can be chemically induced, also reveals improved main root growth.

The pool of reduced plastoquinone (PQH2) is larger in state-transition mutants © L.Leverne/CEA

The results of this study suggest that photosynthetic mutants with a deregulated ratio of photosystem II to photosystem I activity may offer a new avenue of study for improving crop resistance to drought.

Contact : Anja Krieger-Liszkay ( ; )

Plastoquinone is an electron transporter located on the membrane of thylakoids (membrane compartments inside chloroplasts and cyanobacteria), which plays an essential role in photosynthesis.

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