Phosphorylated transcription factor PuHB40 is involved in ROS-dependent anthocyanin biosynthesis in pear exposed to high-light stress

As sessile organisms, plants are increasingly vulnerable to environmental stresses because of global warming and climate change. Stress-induced reactive oxygen species (ROS) accumulation results in plant cell damages and even cell death. Anthocyanins are important antioxidants that scavenge ROS to maintain ROS homeostasis. However, the mechanism underlying ROS-induced anthocyanin accumulation is unclear. In this study, we determined that in pear the HD-Zip I family member PuHB40 mediates ROS-dependent anthocyanin biosynthesis under high-light stress. Specifically, PuHB40 is a transcription factor that induces PuMYB123-like/PubHLH3 complex for anthocyanin biosynthesis. The transcriptional activation by PuHB40 depends on its phosphorylation level, which is regulated by protein phosphatase 2A (PP2A). High ROS contents maintain the phosphorylation of PuHB40 at a high level, while also enhancing PuHB40-induced PuMYB123-like transcription by decreasing the transcription of PuPP2AA2, ultimately leading to increased anthocyanin biosynthesis. Our study revealed the pathway regulating ROS-induced anthocyanin biosynthesis in pear, further clarifying the mechanism underlying abiotic stress-induced anthocyanin biosynthesis, which may have implications for improving plant stress tolerance.