2022_02 A Microtubule Motor as Plant Thermometer

What was the question behind this work? Climate change is more than hot and dry summers, but also blurred seasonality. A warm March, followed by a frosty April mean often huge losses in fruit and grapevine culture. How can plants sense cold stress and respond rapidly to this challenge? We found a curious thermometer - a motor protein that moves along microtubules in the warm, but detaches in the cold and migrates into the nucleus to form enigmatic structures (more...). Therefore, we baptised this motor Dual Localisation Kinesin (DLK). What is the meaning of this strange behaviour.

How did we address the question? We investigated rice mutants, where this motor is inactivated to infer its function. Then we purified the motor in bacteria, to find out, whether it binds to specific sequences on the DNA. Then we overexpressed the motors and monitored the effect on gene expression.

What die we find out? When the motor is mutated, this leads to death of the embryo, when one intact copy is retained, the seedlings survive for a certain time, but have problems to grow. A second look revealed that the response of cell elongation to auxin is perturbed, which is linked with the role of microtubules for cell growth. The search for target sequences on the DNA was successful, we identified a specific recognition motif. The response of cold induced genes in tobacco changes not significantly upon overexpression of DLK. There is one exception, though: the gene switch Cold Box Factor 4 a regulator of cold hardening, is downmodulated. Interestingly, the promoter of this gene switch harbours the recognition motif. Thus, we can show that DLK detaches from microtubules under cold stress, moves into the nucleus and modulates there a gene switch controlling the adaptation to cold stress. This motor is, thus, a plant thermometer, which offers interesting options for application that we want to explore in the future.

Publication 180. Xu A, Hummel S, Harter K, Kolukisaoglu U, Riemann M, Nick P (2022) The Minus-End-Directed Kinesin OsDLK Shuttles to the Nucleus and Modulates the Expression of Cold Box Factor 4. Int J Mol Sci 23, 629 - pdf