UV-B-induced molecular mechanisms of stress physiology responses in the major northern Chinese coniferPinus tabuliformisCarr.

During their lifetimes, plants are exposed to different abiotic stress factors eliciting various physiological responses and triggering important defense processes. For UV-B radiation responses in forest trees, the genetics and molecular regulation remain to be elucidated. Here, we exposed Pinus tabuliformis Carr., a major conifer from northern China, to short-term high-intensity UV-B and employed a systems biology approach to characterize the early physiological processes and the hierarchical gene regulation, which revealed a temporal transition from primary to secondary metabolism, the buildup of enhanced antioxidant capacity and stress-signaling activation. Our findings showed that photosynthesis and biosynthesis of photosynthetic pigments were inhibited, while flavonoids and their related derivates biosynthesis, as well as glutathione and glutathione S-transferase mediated antioxidant processes, were enhanced. Likewise, stress-related phytohormones (jasmonic acid, salicylic acid and ethylene), kinase and reactive oxygen species signal transduction pathways were activated. Biological processes regulated by auxin and karrikin were, for the first time, found to be involved in plant defense against UV-B by promoting the biosynthesis of flavonoids and the improvement of antioxidant capacity in our research system. Our work evaluated the physiological and transcriptome perturbations in a conifer's response to UV-B, and generally, highlighted the necessity of a systems biology approach in addressing plant stress biology.