The plastid-nucleus localized DNA-binding protein WHIRLY1 is required for acclimation of barley leaves to high light.

MAIN CONCLUSION: In accordance with a key role of WHIRLY1 in light-acclimation mechanisms, typical features of acclimation to high light, including photosynthesis and leaf morphology, are compromised in WHIRLY1 deficient plants. Acclimation to the environment requires efficient communication between chloroplasts and the nucleus. Previous studies indicated that the plastid-nucleus located WHIRLY1 protein is required for the communication between plastids and the nucleus in situations of high light exposure. To investigate the consequences of WHIRLY1 deficiency on the light acclimation of photosynthesis and leaf anatomy, transgenic barley plants with an RNAi-mediated knockdown of HvWHIRLY1 were compared to wild-type plants when growing at low and high irradiance. While wild-type plants showed the typical light acclimation responses, i.e. higher photosynthetic capacity and thicker leaves, the WHIRLY1 deficient plants were not able to respond to differences in irradiance. The results revealed a systemic role of WHIRLY1 in light acclimation by coordinating responses at the level of the chloroplast and the level of leaf morphology.