Abstract
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 reported 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 was not increased 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 understanding the mechanism underlying the switch in direction of chloroplast relocation in response to light and temperature.
Highlights
Plants sense ambient light and temperature to adapt to an ever-changing environment
The results suggest that the cold-avoidance response is similar to the avoidance response induced by strong light, and that there is a transitional light intensity that serves as an inflection point between the accumulation and cold-avoidance responses
We considered the possibility that increases in endogenous phot expression may play a role in the decrease in transitional light intensity, as previous studies using A. capillus-veneris and A. thaliana suggest that a reduction in the transitional light intensity can be the result of artificial overexpression of phot [11,12]
Summary
Plants sense ambient light and temperature to adapt to an ever-changing environment. In response to the light and temperature changes, the intracellular chloroplast position is precisely controlled. Under weak-light conditions (e.g., under canopy), chloroplasts move. Cold-induced switch in direction of chloroplast relocation [https://www.jst.go.jp/EN/]; and the Plant Transgenic Design Initiative of the University of Tsukuba to Y.K, URL [https://gene.t-pirc.tsukuba. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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