Increased anthocyanin accumulation and plant growth by driving PAP1 expression using the 3'downstream region of the sulfate transporter SULTR2;1 gene.

High-level expression systems in plants are required for basic research or to enhance the desired traits. However, most expression systems modify the upstream region of the native gene, which can result in loss of expression characteristics. In a previous study, we found that the 3′ downstream region of the sulfate transporter SULTR2;1 gene (TSULTR2;1) is responsible for increased gene expression under sulfur deficiency (−S), regardless of the 5′ upstream region used in the system. In this study, we aimed to establish an expression regulation system based on sulfate concentration using this downstream region. We selected PAP1, a positive regulator of anthocyanin biosynthesis, to test the system. The upstream and coding regions of the PAP1 gene were fused to TSULTR2;1 and the construct was introduced into Arabidopsis thaliana. Under −S, the transgenic roots exhibited higher PAP1 gene expression than wild-type roots. This increase led to elevated transcripts of anthocyanin biosynthetic enzymes, sometimes resulting in a noticeable change in root color to purple due to anthocyanin accumulation. PAP1 gene expression and anthocyanin content also increased by transferring the plants to −S conditions. Furthermore, the transgenic plants demonstrated increased plant growth regardless of S conditions and expressed a higher tolerance to salt stress than the wild-type plants, owing to the increased antioxidant activity, which was likely caused by anthocyanin accumulation. These results indicate the potential of TSULTR2;1 as a tentative target for gene expression technology in plant roots and highlight the positive effects of root anthocyanin accumulation on plant growth.