The conserved active site aspartate residue is required for the function of the chloroplast atypical kinase ABC1K1.

Introduction: The Arabidopsis (Activity of BC1 complex/proton regulation 6) mutant is characterized by photosynthetic and conditional developmental phenotypes triggered by stressful red as well as high light. The Arabidopsis ABC1-like kinases belong to the atypical kinase family and contain conserved ATP-binding and hydrolysis motifs, but their physiological requirement has never been investigated.

Methods: By mutation to asparagine, we demonstrate that the highly conserved active site aspartate residue within ATP-binding motif VIIb is required for the physiological functions of ABC1K1.

Mutation of the Atypical Kinase ABC1K3 Partially Rescues the PROTON GRADIENT REGULATION 6 Phenotype in .

Photosynthesis is an essential pathway providing the chemical energy and reducing equivalents that sustain higher plant metabolism. It relies on sunlight, which is an inconstant source of energy that fluctuates in both intensity and spectrum. The fine and rapid tuning of the photosynthetic apparatus is essential to cope with changing light conditions and increase plant fitness.

Plastoquinone homoeostasis by proton gradient regulation 6 is essential for photosynthetic efficiency.

Photosynthesis produces organic carbon via a light-driven electron flow from HO to CO that passes through a pool of plastoquinone molecules. These molecules are either present in the photosynthetic thylakoid membranes, participating in photochemistry (photoactive pool), or stored (non-photoactive pool) in thylakoid-attached lipid droplets, the plastoglobules. The photoactive pool acts also as a signal of photosynthetic activity allowing the adaptation to changes in light condition.