Abstract
One important component of the cytokinin signaling pathway is the histidine phosphotransferase (HP), which plays an essential role in regulating downstream gene expression by transferring phosphate groups. The role of histidine phosphotransfer proteins (HPs) in sugar beets under abiotic and biotic stresses remains unclear. The results showed that the expression of BvHP4b in red beets increased in response to the exogenous hormone 6-BA. Transgenic Arabidopsis seedlings with heterologous expression of BvHP4 T3 lines (BvHP4-OE) displayed enhanced growth and resistance to Pst DC3000. Moreover, the expression of NPR1 and PRs was increased in the T3 transgenic lines compared to the control. Subcellular localization analysis revealed that BvHP4b primarily localized to the cell membrane. Transgenic red beets overexpressing BvHP4b (BvHP4b-OX lines) and bvhp4b mutant plants (KO lines) using CRISPR/Cas9 technology were generated respectively. The BvHP4b-OX lines showed enhanced taproot development, which was attributed to the altered expression of BvXTH33, BvCESA6, BvCDC2, and BvCEL1 genes. These lines also exhibited increased tolerance to Pst DC3000 by regulating synthesis of SA and modulating the expression of genes involved in plant immunity. In contrast, the KO plants were more susceptible to Pst DC3000 compared to the control plants. Furthermore, BvHP4b was shown to interact with BvCDC2 both in vivo and in vitro. Overall, this study suggests that the BvHP4b protein acts as a positive regulator, enhancing taproot enlargement and tolerance to Pst DC3000 in sugar beet plants.