Study On Cross Adaptation Of Drought Induced To Chilling Stress In Tea Seedlings

In order to find out the physiological and molecular mechanisms of drought-low temperature cross adaptation of tea plans,seedlings from annual Shuchazaocha[Camellia sinensis(L.)O.Kuntze]were used as materials to carry out a experiment.Seedlings were pretreated under drought condition,which simulated with polyethylene glycol-6000(PEG-6000).The effects of drought pretreatment on tea seedling resistance at low temperature and antioxidant enzyme system,osmotic adjustment and hormonal regulation in tea plans were studied;The molecular mechanism of drought-low temperature cross-adaptation was analyzed by second-generation transcriptome sequencing technology.The results are as follows:1.The semi-lethal temperature LT50 of tea seedlings pretreated with PEG decreased significantly.Under low temperature,the content of MDA,antioxidant enzyme activity,osmotic substances and hormones in tea seedlings increased as a whole.On the 7th day of low temperature stress,compared with the control,the MDA content of tea leaves pretreated with PEG decreased by 44.6%,SOD and POD activity increased by 78%and 25%,soluble protein and soluble sugar increased by 44.6%and 20.0%,and the contents of plant endogenous hormones ABA and SA increased by 97.7%and 122%,Drought can induce cross-adaptability of tea plants to low temperature stress,which is related to the regulation of antioxidant enzymes,osmotic substances and endogenous hormones.2.The transcriptome was sequenced in the drought pretreatment group,the low temperature group and the normal group.Three biological replicates were used in each treatment group,and nine cDNA libraries were constructed.Through the Illumina HiSeq 4000 platform for sequencing,a total of 71.31 Gb raw data was obtained,each group of samples exceeded 47,375,100 reads,and the raw data was filtered to obtain valid data of 70.39 Gb,and the reference gene alignment rate reached 82%;Compared with CK,the differential expressed genes induced by drought-low temperature cross stress were 71.9%less than that of low temperature;Venn’s graph showed that there were 81 common genes in the three groups,involving 107 GO functional annotations;Compared with a single low temperature,the drought-preconditioned differential expressed gene GO function enriched 221 biological processes,including significant enrichment in the antioxidant reduction process and glutathione metabolism;KEGG pathway in the antioxidant enzyme metabolic pathways and classes Enrichment in the flavonoid metabolic pathway.Therefore,it is hypothesized that this cross-adaptive regulatory gene may be involved in the ROS metabolic pathway,the glutathione synthesis pathway,and the flavonoid metabolic pathway.3.In the glutathione synthesis pathway,the key enzyme GS-CSA024544 gene was significantly up-regulated in drought pretreatment.It indicates that drought pretreatment can increase the up-regulated expression of GS key enzyme gene,which is beneficial to the synthesis of glutathione.In the reactive oxygen species(ROS)pathway map,SOD enzyme and POD enzyme genes were up-regulated in drought pretreatment;In the flavonoid metabolic pathway,chalcone synthase(CHS),flavonol synthase(FLS)and flavanone-3-hydroxylase(F3H)genes are up-regulated,it has a unique inhibitory effect on the anthocyanin reductase(LAR)gene involved in the biosynthesis of catechin and gallocatechin.In addition,some differentially expressed genes in three metabolic pathways were verified by fluorescence quantitative q-PCR,and the results were basically consistent with the results of transcriptome sequencing.Therefore,it is concluded that drought pretreatment can induce key enzyme genes in glutathione synthesis pathway,ROS metabolic pathway and flavonoid metabolic pathway to improve the cold resistance of tea trees.