Sugars promote graft union development in the heterograft of cucumber onto pumpkin

The use of heterografts is widely applied for the production of several important commercial crops,but the molecular mechanism of graft union formation remains poorly understood.Here,cucumber grafted onto pumpkin was used to study graft union development,and genome-wide tempo-spatial gene expression at the graft interface was comprehensively investigated.Histological analysis suggested that resumption of the rootstock growth occurred after both phloem and xylem reconnection,and the scion showed evident callus production compared with the rootstock 3 days after grafting.Consistently,transcriptome data revealed specific responses between the scion and rootstock in the expression of genes related to cambium development,the cell cycle,and sugar metabolism during both vascular reconnection and healing,indicating distinct mechanisms.Additionally,lower levels of sugars and significantly changed sugar enzyme activities at the graft junction were observed during vascular reconnection.Next,we found that the healing process of grafted etiolated seedlings was significantly delayed,and graft success,xylem reconnection,and the growth of grafted plants were enhanced by exogenous glucose.This demonstrates that graft union formation requires the correct sugar content.Furthermore,we also found that graft union formation was delayed with a lower energy charge by the target of rapamycin(TOR)inhibitor AZD-8055,and xylem reconnection and the growth of grafted plants were enhanced under AZD-8055 with exogenous glucose treatment.Taken together,our results reveal that sugars play a positive role in graft union formation by promoting the growth of cucumber/pumpkin and provide useful information for understanding graft union healing and the application of heterografting in the future.

Interference of CsGPA1,theα-submit of G protein,reduces drought tolerance in cucumber seedlings

The G proteinα-subunit,GPA1,is an integral component of several signaling pathways in plants,including response to abiotic stress.However,the molecular mechanism behind these processes remains largely unknown in the cucumber plant(Cucumis sativus L.).In order to further understand the role of CsGPA1 in cucumber under drought stress,changes in plant growth,physiological parameters,and gene expression of CsAQPs were all measured under water stress induced by polyethylene glycol(PEG)using wild type(WT)and CsGPA1-interference(RNAi)cucumber seedlings.Our results demonstrated that the RNAi plants had lower drought tolerance,displaying seriously withered leaves,lower relative growth rate,lower root-shoot ratio,and lower root activity under drought stress compared to WT plants.Physiological studies indicated that the suppression of CsGPA1 weakened drought stress tolerance due to higherwater loss rate in the leaves,higher levels of hydrogen peroxide(H2O2),increased malondialdehyde(MDA)content,lower free proline content,lower soluble sugar content,lower soluble protein content,and decreased antioxidant enzyme activities.qRT-PCR analysis demonstrated that the interference of CsGPA1 up-regulated the expression of most AQP genes(except for CsPIP2;3 in leaves)and down-regulated the expression of CsPIP1;2,CsPIP1;4,CsPIP2;1,and CsPIP2;4 in roots under drought stress when compared to WT plants.Our results demonstrated that CsGPA1 could function as a positive regulator in drought stress response by decreasing the accumulation of reactive oxygen species(ROS),improving permeable potentials,and reducing water loss in cucumber plants.