Plant plasmodesmata (PDs) are specialized channels that enable communication between neighboring cells.The intercellular permeability of PDs,which affects plant development,defense,and responses to stimuli,must be tightly regulated.However,the lipid compositions of PD membrane and their impact on PD permeability remain elusive.Here,we report that the Arabidopsis sld1 sld2 double mutant,lacking sphingolipid long-.chain base 8 desaturases 1 and 2,displayed decreased PD permeability due to a significant increase in callose accumulation.PD-located protein 5 (PDLP5) was significantly enriched in the leaf epidermal cells of sld1 sld2 and showed specific binding affinity to phytosphinganine (t18:0),suggesting that the enrichment of t18:0-based sphingolipids in sld1 sld2 PDs might facilitate the recruitment of PDLP5 proteins to PDs.The sld1 sld2 double mutant seedlings showed enhanced resistance to the fungal-wilt pathogen Verticillium dahlia and the bacterium Pseudomonas syringae pv.tomato DC3000,which could be fully rescued in sld1 sld2 pdlp5 triple mutant.Taken together,these results indicate that phytosphinganine might regulate PD functions and cell-to-cell communication by modifying the level of PDLP5 in PD membranes.