PT  - JOURNAL ARTICLE
AU  - Yuta Fujii
AU  - Yuka Ogasawara
AU  - Saori Tamura
AU  - Yutaka Kodama
TI  - Chloroplast cold-avoidance response in <em>Marchantia polymorpha</em> occurs independently of changes in endogenous phototropin expression
AID  - 10.1101/544361
DP  - 2019 Jan 01
TA  - bioRxiv
PG  - 544361
4099  - http://biorxiv.org/content/early/2019/02/08/544361.short
4100  - http://biorxiv.org/content/early/2019/02/08/544361.full
AB  - When exposed to fluctuating light intensity, chloroplasts move towards weak light (accumulation response), and away from strong light (avoidance response). In addition, cold treatment (5°C) induces the avoidance response even under weak light conditions (cold-avoidance response). These three responses are mediated by the phototropin (phot), which is a blue-light photoreceptor and has also been found to act as a thermosensory protein that perceives temperature variation. Our previous report indicated that cold-induced changes in phot biochemical activity initiate the cold-avoidance response. In this study, we further explored the induction mechanism of the cold-avoidance response in the liverwort Marchantia polymorpha and examined the relationship between changes in the amount of phot and the induction of the cold-avoidance response. The switch between the accumulation and avoidance responses occurs at a so-called ‘transitional’ light intensity. Our physiological experiments revealed that a cold-mediated decrease in the transitional light intensity leads to the induction of the cold-avoidance response. While artificial overexpression of phot decreased the transitional light intensity as much as cold treatment did, the amount of endogenous phot remained unchanged by cold treatment in wild-type M. polymorpha. Taken together, these findings show that the cold-avoidance response is initiated by a cold-mediated reduction of the transitional light intensity, independent of the amount of endogenous phot. This study provides a clue to understand the mechanism underlying the switch in direction of chloroplast relocation in response to light and temperature.