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. Background Various abiotic stresses, including high-light intensity, promote the accumulation of anthocyanins in plants, while also activating the production of reactive oxygen species (ROS). Anthocyanins can attenuate the negative effects of high-light stress by acting as antioxidants that restrict ROS accumulation. Several reports have shown that ROS can stimulate anthocyanin accumulation, but whether high-light stress-induced anthocyanin accumulation depends on ROS is undetermined. Additionally, the mechanism underlying ROS-dependent anthocyanin biosynthesis remains unclear. Question Does high-light stress-induced anthocyanin biosynthesis depend on ROS? What is the molecular basis of high-light stress-induced anthocyanin biosynthesis? Findings High-light stress-induced anthocyanin biosynthesis in pear seedlings is dependent on ROS accumulation. PuMYB123-like is the key MYB transcription factor for anthocyanin biosynthesis, while PuHB40 activates anthocyanin biosynthesis in response to ROS under high-light stress. Specifically, PuHB40 activates the transcription of PuMYB123-like , with the encoded protein combining with PubHLH3 to form an MBW complex that promotes anthocyanin biosynthesis. The transcriptional activation by PuHB40 depends on its phosphorylation status, which is regulated by protein phosphatase 2A (PP2A). High ROS levels inhibit the transcription of PuPP2AA2 , thereby maintaining the phosphorylation of PuHB40, enhancing the transcriptional activation by PuHB40, inducing PuMYB123-like transcription, and ultimately leading to increased anthocyanin biosynthesis. Next steps Our future research will focus on whether ROS and the MYB123-like– PuHB40–PP2A regulatory module are also involved in the anthocyanin biosynthesis induced by other abiotic and biotic stresses, which will provide insights into biotic stress-induced anthocyanin biosynthesis and form the theoretical basis for improving fruit coloration. ### Competing Interest Statement The authors have declared no competing interest.