Effects of Foliar Selenium Treatment on Phenolic Antioxidant Compound Accumulation and Transcriptomic Profiles in Developing Black Wheat Grains.

Selenium (Se) foliar spraying improves grain nutritional quality of pigmented wheat, yet the physiological and molecular regulatory mechanisms of Se-mediated anthocyanin accumulation in black wheat remain poorly understood. In this study, six concentrations of sodium selenite (0-150 mg·L-1, 0 mg·L-1 served as the blank control) were foliarly applied to black wheat Nongda 3753 and white wheat Jimai 22 to screen the optimal Se dosage. Dynamic changes in grain antioxidants across multiple time points throughout grain filling were characterized, and transcriptome sequencing combined with an Arabidopsis mutant functional assay was performed to dissect the regulatory network. The results showed that grain Se content in Nongda 3753 reached its peak (0.61 mg·kg-1) under the 150 mg·L-1 treatment, representing a 555.63% increase over the control. Under the 75 mg·L-1 treatment, total phenolics (2.68 mg GAE·g-1), total flavonoids (2.96 mg rutin·g-1), and DPPH scavenging rate (89.02%) all reached their maximum levels; therefore, 75 mg·L-1 was determined as the optimal compromise dosage for comprehensive grain quality improvement. Through temporal profiling, 25 days after anthesis (DAA) was identified as the critical Se-responsive stage, at which anthocyanin content reached its highest level among all time points (117.08 mg·kg-1), showing a significant increase of 25.13% compared with the control at the same time point, and the anthocyanin biosynthesis pathway was uniquely enriched. The anthocyanidin synthase (ANS) gene was specifically upregulated by Se, and nine key transcription factors were screened. Functional verification revealed that TaMYB20-like acts as a negative regulator of anthocyanin accumulation. This work clarifies the temporal pattern and molecular basis of Se-enhanced antioxidant synthesis, offering gene targets for Se-enriched functional wheat breeding.