Characterization and functional analysis of pollen-specific PwSWEET1 in Picea wilsonii

SWEET transporters play a pivotal role in sugar transport in plants. However, their functions in pollen tube growth, especially in coniferous species remain unknown. Here, we used RT-qPCR to reveal that a SWEET1 gene was specifically expressed in pollen and pollen tubes of Picea wilsonii. A pollen germination assay showed that PwSWEET1 was induced by H3BO3 but not by Ca2+. In a sugar specificity experiment, sucrose (Suc) and glucose (Glc) were effective sugars for pollen germination and pollen tube growth. PwSWEET1 expression was induced most by Suc and Glc. Heterologous expression of PwSWEET1 in yeast showed that PwSWEET1 can restore the glucose absorption in yeast strain EBY.VW4000, which has a hexose absorption defect, and the absorption of glucose is pH-independent. This evidence supports the involvment of PwSWEET1 in boron-dependent glucose transport in pollen germination and pollen tube growth of Picea wilsonii.