PpybZIP43 contributes to sucrose synthesis in pear fruits by activating PpySPS3 expression and interacts with PpySTOP1.

Sucrose is an important factor affecting sweetness and flavor in pear fruits, but the molecular mechanism of sucrose synthesis regulation is relatively unknown. Here, we characterized a transcription factor gene from pear (Pyrus pyrifolia Nakai cv. "Hosui") fruits, PpybZIP43, and found that the transient overexpression of PpybZIP43 in pear fruits significantly increased the sucrose content and the relative expression level of sucrose phosphate synthase genes (PpySPS3 and PpySPS8). Subcellular localization analysis in tobacco leaves showed that PpybZIP43 was localized in the nucleus. Yeast one-hybrid, electrophoretic mobility shift assay (EMSA), and dual-luciferase reporter assays indicated that PpybZIP43 was able to activate the expression of PpySPS3 by binding specifically to the G-box (CACGTG) element in the promoter. The protein-protein interaction assays using yeast two-hybrid, bimolecular fluorescence complementation (BiFC), firefly luciferase complementation imaging (LCI), and glutathione S-transferase (GST) pull-down demonstrated that PpybZIP43 could directly interact with PpySTOP1 to form a transcription complex. This study is helpful for understanding the molecular basis of sucrose synthesis and accumulation in pear fruits and provides candidate genes for breeding.