Carotenoids participate in adaptation/resistance of daily desiccation in the intertidal red alga Neopyropia yezoensis (Bangiales, Rhodophyta)

Abstract

The intertidal zone is one of the most critical and extremely harsh ecosystems. Unlike intertidal animals that might employ evasive behavior, intertidal plants such as seaweeds have to suffer daily rhythmic stresses such as water loss, low temperature, and high irradiation caused by submersion and emersion. How they survive or even successfully adapt to such a harsh environment has drawn much attention. Porphyra (sensu lato) (bladed Bangiales) is such a group of intertidal red algal seaweeds with significant economic, social and ecological value. Given their long evolutionary history dated back to 500–1000 Mya, Porphyra species have evolved multiple and subtle mechanisms coping with the harsh intertidal environment, making them ideal candidates for studying the stress adaptation mechanisms. However, studies on stress adaptation mechanisms of Porphyra are scarce and not systematic. We analyzed the desiccation adaptation/resistance mechanisms of Neopyropia yezoensis (originally named Porphyra yezoensis) concerning carotenoid biosynthesis in the present work. Dehydration treatment was conducted on the haploid thalli to determine the variations in gene expression pattern, carotenoid content, reactive oxygen species content, and photosynthetic activity. Physiological responses indicated that desiccation alone did not cause significant damages to the thalli, and carotenoids respond to and participate in adaptation/resistance of desiccation. Losing 60% of its water content was identified to be a turning point for N. yezoensis thallus during desiccation. Below this point, photosynthesis and carotenoid biosynthesis were both downregulated to adapt to the desiccation passively. In contrast, the biosynthesis of antioxidants such as carotenoids was upregulated above this point, probably for scavenging the ROS caused by severe dehydration. The transcriptional regulation of enzyme genes for carotenoid biosynthesis during desiccation is also discussed.