Physiological And Molecular Mechanisms Of Drought Tolerance Affected By Grafting In Tobacco

Using the drought-sensitive cultivar Jinxing6007 as a scion,Jinxing6007 and drought-tolerant cultivar Longjiang851 as rootstocks,the self-grafted(JX6007/JX6007)and rootstock-grafted(JX6007/LJ851)tobacco plants were produced by grafting.After normal and drought treatment,we focused on the physiological and molecular mechanism of drought resistance of grafting tobacco by determination of physiological and biochemical indexes and transcriotome analysis.The main results we obtained were as follows:(1)JX6007/LJ851 performed better under drought stress,the biomass,the content of chlorophyll and antioxidant enzyme activities of JX6007/LJ851 were significantly increased,while MDA and H2O2 contents were decreased relative to JX6007/JX6007.(2)Using RNA-seq to different grafting tobacco during drought stress,we found 32487 Unigenes noted the NR database from the sequencing result.A preliminary analysis showed that there were 4013 differentially expressed genes in JX6007/JX6007,which 1176 up-and 2837 down-regulated transcripts during drought stress,while 4466 differentially expressed genes in JX6007/LJ851,containing 3247 up-regulated genes,1219 up-regulated genes.We found that these genes were mainly related to biological and abiotic stimuli,plant hormone signal transduction and photosynthesis by GO and KEEG pathway analysis,including 1599 differentially expressed genes annotated in the tobacco genome information.KEGG pathways involved 120 ways,3486 Unigenes,these prediction ways represent the biological synthesis,degradation and the assimilation process of most plants.we also found 15 kinds of metabolic pathways which were significantly different in the two kinds of grafting combinations under drought stress,and these pathways mainly involved plant hormone signal transduction,photosynthesis and nitrogen metabolism,which strongly suggested JX6007/LJ851 may promote related genes expression to enhance drought resistance.(3)Transcript levels of 10 genes were determined by q RT-PCR,including 4 differentially expressed genes: CDC48,CSC1,TAS14 and unknown gene,related to plant hormone signal transduction,3 transcription factors:b HLH87,TGA7 and DREB-1E,2 genes: LEA D-34 and LTP1 related to stress response,and GBE1 related to Metabolic pathways.The result showed that the relative expression level of 5 genes was down-regulated in JX6007/JX6007 under drought stress,but up-regulated in JX6007/LJ851.The relative expression level of another 5 genes is up-regulated in two grafting combinations,but in JX6007/LJ851 much higher than in JX6007/JX6007.These results may suggest that 10 genes may participate in the drought resistance process of rootstock-grafted tobacco.The above research indicated that grafting can affect the drought tolerance of tobacco by regulating plant antioxidase system and expression of drought tolerance related genes,it provides evidence to explain deeply the molecular mechanisms of plant stress resistance affected by grafting.