The Mechanism Of H₂S In Low Temperature-Induced Cucurbitacin C Increases And Resistance To Phytophthora Of Cucumber

Cucurbitacin C?CuC?is a highly oxidized triterpenoid secondary metabolite,which was first discovered in cucumber leaves in 1954.It can enhance the resistance of cucumber plants to pathogenic bacteria and insect herbivores,but result in bitter-tasting fruit.CuC could be induced in some varieties of cucumber when they suffered indisposed environment.In addition,CuC has potential medicinal value,which can help people improve immunity and treat chronic hepatitis.Due to the influence of CuC on the tasting quality and its pharmacological effects,the synthesis regulation,separation and purification of CuC has been widely concerned.In plants,H₂S signaling is also involved in the physiological functions of plants against multiple abiotic stresses,but deeper mechanisms and signaling pathways still need further study.In this study,cucumber variety 9930 was used as experimental material,and the molecular mechanism of H₂S in regulating CuC synthesis when cucumber suffering low temperature stress was researched.The main results are as follows:1.The H₂S content,H₂S production rate,and the expression of H₂S producing enzyme genes Csa LCD?Csa2G034800.1?,Csa DES1?Csa1G574800.1?and Csa DES2?Csa1G574810.1?in cucumber leaves were increased at 4? for 12 h.2.4? or exogenous H₂S treatment up-regulated the expression of CuC synthetase encoding genes and the CuC content in cucumber leaves,while hypotaurine?HT,a H₂S scavenger?pretreatment weakened the inducing effect that caused by 4? treatment.In vitro,recombination proteins His-Csa5G156220 and His-Csa5G157230,which were b HLH transcription factors in cucumber,were experienced S-sulfhydration after H₂S treatment,and showed a increased binding activity to the promoter of Csa6G088690,which encodes the key synthetase for CuC generation.3.H₂S pretreatment enhanced the cucumber leaves resistance to the phytophthora melonis.In addition,the gene expression of L-type lectin receptor kinase 6.1?Lec RK6.1?,Chitinase,and Glucanase were up-regulated by H₂S pretreatment.In summary,H₂S can improve the binding activity of His-Csa5G156220 and His-Csa5G157230 to the promoter of Csa6G088690 gene,by S-sulfhydration modification on the two b HLH tranccription factors,resulting in an increase of CuC synthetase encoding genes expression in cucumber under low temperature.H₂S increased the CuC content and PR genes expression to enhance cucumber resistance to the phytophthora melonis.This paper provided the evidence for H₂S improving plant res istance to biological stress,and supported that H₂S and its related preparations would function as a possible crop disease activators.