Temperature Adaptability And Transcriptome Analysis Of Phytophthora Infestans

Phytophthora infestans is an important pathogen of potato,late blight which caused by P.infestans can result in great losses in potato production.Temperature is an important factor for pathogen’s growth,development,and reproduction.Extreme weather caused by global warming frequently occurs,and the knowledge about how pathogens adapt to changing temperature is essential for crop disease prevention and control.In this study,the growth rate,germination rate of sporangia,zoospore release rate and the length of germ tube germinated by sporangia of P.infestans isolates sampled from four regions-Guangxi,Yunnan,Gansu and Inner Mongolia were performed under three constant temperatures(12℃,18℃,25℃)and one variable temperature.The aims of this study were to determine the effect of temperature on P.infestans,and to ascertain whether there are regional differences of P.infestans in response to different temperatures.Furthermore,it will provide a theoretical basis for pathogen in response to changing experimental temperatures.To further explore the molecular mechanism of how P.infestans responses to extreme temperatures,four strains EYS9-41,AL-6,AYS5-2,and Pd11229 which showed great effect on low and high temperatures were selected for transcriptome and cultured at 12℃,18℃and 25℃,to explore how mycelial growth,sporangia germination and zoospore release of P.infestans response to changing temperature.The results obtained are shown below:1.The effect of temperature on P.infestans in different regions:Statistical analysis were performed on the growth rate,sporangia germination rate,zoospore release rate and length of germ tube germinated by sporangia of P.infestans in 4 regions at different temperatures in this thesis,the results showed that P.infestans have both temperature adaption and local adaption.The overall,optimal temperature for mycelium growth was 18 ℃,followed by variable temperature,12℃and 25℃,respectively.The growth rate of P.infestans from Guangxi region with the highest annual average temperature is the highest,followed by the average annual temperature ranked second,third and the lowest in Yunnan,Gansu and Inner Mongolia.The sporangia germination rate was highest at 18 ℃,followed by 25 ℃,variable temperature and 12℃,and the germination rate of sporangia in Gansu,was significantly higher than other regions.The zoospore released rate from higher to lower was 12℃,variable temperature conditions,18℃,and 25℃,and the released rate of zoospores in Gansu,was significantly lower than in other areas.The optimal temperature for germ tube growth was 18℃ and variable temperature,low or high temperature is not beneficial for germ tube to grow,and the length of sporangia germ tube from Guangxi,was significantly higher than other regions,the length of sporangia germ tube from Guangxi was highest and shortest at Yunnan.2.Transcriptome analysis of P.infestans at different temperatures: 4strains showed great effect on low and high temperatures were selected for transcriptome and cultured at 12℃,18℃ and 25℃ in this thesis.The results showed that there is 3874 DEGs at low temperature of 12℃ and only 5 DEGs common to the four strains.There is 4286 DEGs at high temperature of 25℃ and only 8 DEGs common to the four strains.4HSP-like genes,9 HSP genes and 37 sporangia-related genes were identified among the temperature related genes.DEGs are mainly enriched in the functions of carbohydrate metabolic process,endocytosis,integral component of membrane,extracellular region and phosphatidylinositol binding at 12 ℃,while in the functions of carbohydrate metabolic process,integral component of membrane,calcium ion binding and phosphatidylinositol binding at 25℃.DEGs are mainly involved in ribosome,antibiotic biosynthesis and endocytosis at low temperature of 12 ℃,while in metabolic pathway,secondary metabolite biosynthesis and antibiotic biosynthesis at high temperature of25℃.3.qPCR verification of DEGs: Eight genes with a significant fold differences in expression common to three or four strains were selected for q PCR verification,and eight P.infestans strains were selected to verify the expressions level at 12℃,18℃and 25℃.Among them,two DEGs PITG＿11238 and PITG＿15858 were down-regulated in all the samples at 25℃,and the results were consistent with the transcriptome results.The other six DEGs were up-regulated in some samples,while down-regulated in other samples,which is consistent with the transcriptome results were some DEGs differs in expression in different samples,indicating that there is an individual difference in their response to temperatures.