Protective role of anthocyanins in plants under low nitrogen stress.

Nitrogen (N) is a major nutrient of plants but often a limiting factor for plant growth and crop yield. To adapt to N deficiency, plants have evolved adaptive responses including accumulation of anthocyanins. However, it is still unclear whether the accumulated anthocyanins are part of the components of plant tolerance under low N stress. Here, we demonstrate that low N-induced anthocyanins contribute substantially to the low N tolerance of Arabidopsis thaliana. pap1-1, a mutant defective in MYB75 (PAP1), a MYB-type transcription factor that positively regulates anthocyanin biosynthesis in Arabidopsis, was found to have significantly decreased survival rate to low N stress compared to its wild-type plants. Similarly, tt3, a mutant with severe deficiency in dihydroflavonol 4-reductase (DFR), a key enzyme in anthocyanin biosynthesis, also showed much lower survival rate under low N stress. These results indicate that anthocyanins are substantial contributors of plant tolerance to low N stress. Furthermore, a metabolomics analysis using LC-MS revealed changes in flavonoid profile in the pap1-1 and tt3 plants, which established a causal relationship between plant adaptation to low N stress and these compounds including anthocyanins. Our results showed an important role of anthocyanins rather than flavonols in conferring plant tolerance to low N stress.