Functional interaction of type II phytochromes in Arabidopsis

• Applicant: Dr. Cornelia Klose
• Subject Area: Plant Physiology
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 563967152

Natural environments are complex and highly dynamic where light and temperature conditions can change rapidly and simultaneously. Plants need to detect these changing conditions, integrate the different signals and regulate their physiological responses accordingly to ensure optimal growth and reproduction. Phytochromes are temperature sensitive photoreceptors for the red/far-red light range of the light spectrum, which have an essential function in the detection and integration of light and temperature signals in plants. The spectral composition and intensity of light regulate the reversible phytochrome photoconversion from the inactive Pr state to the active Pfr state and back to Pr. In addition, the inactivation of Pfr into Pr also occurs via a light-independent thermal reversion. In our model plant Arabidopsis thaliana the phytochrome family comprises 5 members, phyA to phyE. Phy B, C, D and E are the light stable type II phytochromes. Phytochromes are dimeric proteins. For phyB, we have previously demonstrated that the the specific properties of the phytochrome dimers and the intracellular phytochrome dynamics determine under which conditions phyB can be physiologically active. PhyC, D and E have been studied much less intensively, mainly because phyA and B dominate many light responses in plants. However, our preliminary data show that phyB alone is not able to mediate light responses at the wild-type level. Interestingly, phyB can occur as homodimer or as heterodimer with phyC, D or E. Based on preliminary results, we conclude that phyC, D and E alone do not have strong activity, but presumably exert their function by modulating the activity of phyB. We further hypothesize that this functional interaction occurs within phytochrome heterodimers with specific properties. These mechanisms could enable plants to greatly extend their range of light and temperature responsiveness. In the proposed project we aim to characterize the dynamic properties of phytochromes C, D and E and their heterodimers with phyB and investigate the mechanisms of functional interaction of phytochromes in heterodimers. This will improve our understanding of how plants to successfully cope with constantly changing environmental conditions.

• DFG Programme: Research Grants