The transcription factor PsLBD42 promotes low nitrogen-induced anthocyanin biosynthesis in poplar

Plants have developed intricate mechanisms to adapt to fluctuating nitrogen availability in the soil, including modulation of anthocyanin biosynthesis. However, the regulation mechanism of lateral organ boundary domain (LBD) transcription factors on anthocyanin biosynthesis under low nitrogen (LN) conditions remains poorly understood. Here, we functionally characterized PsLBD42 from Populus simonii, a class II LBD transcription factor, which was upregulated under LN conditions. PsLBD42-overexpression transgenic poplar exhibited enhanced resistance to the LN stress with increased photosynthetic rates and decreased photooxidation, but unchanged nitrogen content and uptake capability. Meanwhile, the accumulation of anthocyanin was significantly increased in the leaves of PsLBD42-overexpression transgenic poplar. The contrary results were shown in the lines of PsLBD42-suppression transgenic poplar. It was confirmed that PsLBD42 could directly bind to the promoters of PsUGT78D2 and PsUGT79B3 in the genes of anthocyanin pathway by yeast one-hybrid, dual luciferase and ChIP-qPCR assays. Under LN conditions, overexpression of PsUGT78D2 and PsUGT79B3 in the poplar leaves accumulated more anthocyanins while the suppression of PsUGT78D2 and PsUGT79B3 reduced anthocyanins content. Furthermore, overexpression of PsUGT78D2 and PsUGT79B3 restored anthocyanin levels in PsLBD42-RNAi lines under LN conditions. Collectively, our results indicate that the PsLBD42-PsUGT78D2/PsUGT79B3 module regulates anthocyanin accumulation in poplar leaves as a novel mechanism to enhance poplar tolerance to LN stress.