| Drought is a common stress in plant growth.Drought seriously affects plant growth and development,and reduces plant yield.Camellia oleifera is an important edible oil tree species of xylophyta in China,and the main production area of Camellia oleifera is in the hilly mountains of South China.Although July to August is the key period for oil conversion of Camellia oleifera,it has high temperature with less rain from July to September,therefore,makes it difficult to irrigate.High temperature and drought affect the development of Camellia oleifera fruit,causing flower and fruit drop,which has become a major obstacle restricting the development of Camellia oleifera industry.Camellia oleifera is a drought-tolerant tree species.The research on the drought-tolerant mechanism of Camellia oleifera is the theoretical basis for cultivating highly resistant varieties of Camellia oleifera and ensuring the yield of Camellia oleifera.In order to comprehensively analyze the important pathways and gene regulation rules of the formation of drought resistance quality of Camellia oleifera,and to explore the genetic resources related to the formation of resistance quality of Camellia oleifera This paper used two-year-old grafted seedlings as experimental materials to study the physiological and biochemical responses of container seedlings and bare-root seedlings of different varieties of Camellia oleifera to drought stress,and carried out transcriptomics studies on the leaves and roots of Camellia oleifera under drought stress at different periods and rehydration conditions.The main findings are as follows:1.The camellia leaves and roots were observed at different periods of drought stress and after rehydration,the results showed that with the prolonged drought stress,camellia leaves change from green to yellow brown,curly or even fall off,The root system of container seedlings is more developed than bare-root seedlings,and the root cells gradually lose water or even fall off and die.After rewatering,the leaves gradually turn green and the root system gradually recovers.2.The photosynthetic indexes of Camellia oleifera were studied in different periods of drought stress and post-rehydration.The results showed that with the decrease of water content,the net photosynthetic rate(Pn),stomatal conductance(Gs)and transpiration rate(Tr)of Camellia oleifera decreased sharply,but all three increased after rehydration.Under drought stress,intercellular CO2 concentration(Ci)tended to decrease first and then increase,while water use efficiency(WUE)increased first and then decreased.Under severe stress,Pn decreased close to 0 and Ci increased,indicating that severe drought damaged the photosynthetic structure,and the main reason for the decrease of Pn was non-stomatal factors.On the 8th day after rehydration,photosynthetic indexes gradually recovered.3.Antioxidant enzymes and osmotic regulatory substances of Camellia oleifera were measured at different periods of drought stress and after rehydration.The results showed that the content of soluble protein(SP)and salicylic acid(SA)increased with the increase of drought stress.The changes of superoxide dismutase(SOD)and peroxidase(POD)activities were different among different varieties of Camellia oleracea.The SOD activity of’Hua shuo’ increased continuously,while that of ’Hua jin’ decreased first and then increased,and that of’Hua shuo’ container seedlings decreased first and then increased.The POD activity of the other three showed an upward trend.The malondialdehyde(MDA)of ’Hua jin’ container seedlings decreased first and then increased,while the other three showed a continuous increase.After rehydration,SOD,POD,SP and SA decreased,but after rehydration,SP content was higher than that of the first day of drought.The decrease proportion of SA in bare root seedlings was lower than that in container seedlings,and the decrease range of SA in’Hua shuo’ was lower than that in ’Hua jin’.The average content of MDA in the container seedlings of’Hua jin’ decreased,while the content of MDA in other varieties increased to different degrees.There was no significant change in proline(Pro)of’Hua shuo’,and a significant decrease in ’Hua jin’,indicating that although the drought was relieved,the physiological and biochemical activities of Camellia oleifera did not completely recover.4.Transcriptome sequencing of 96 samples of root and leaf showed that a total of 322,551 Unigenes were obtained,with a sequence length of 298,572,221nt,of which 58,720 were annotated in at least one public database,41,826 were annotated in GO,and 17,390 were annotated in Pathway.KEGG pathway classification showed that all genes were involved in 33 metabolic pathways,of which 8,001 genes were involved in carbohydrate metabolism,8,325 genes were involved in signal transduction,and 2,242 genes were related to adaptation.5.The GO and KEGG enrichment of DEGs in roots(BGl-vs-BG10)and leaves(BL1-vs-BL 10)of‘Hua shuo’bare root seedlings were compared the first day and 10th day of drought,and the results showed that BG1-vs-BG10 differentially expressed genes totaled 23,457 unigenes,including 13,810 up-regulated genes and 9,647 down-regulated genes;BLI-vs-BL10 obtained 15,196 DEGs,including 8,077 up-regulated genes and 7,199 down-regulated unigenes.6.GO enrichment results showed that BLI-vs-BL10 and BGl-vs-BG10 have 7,307 and 12,677 unigenes obtained gene annotations respectively.The smallest first 30 enrichment pathways in BLI-vs-BL10 Corrected P-Value,including 15 cytological component pathways such as photosynthetic membrane and membrane intrinsic elements,10 biological process pathways such as photosynthesis and plant hormone,transferase activity,5 molecular functional pathways including chlorophyll binding,mainly related to the cell structure and physiological processes related to leaf photosynthesis.Under drought stress,Differential gene expression in leaves was mainly due to the up-regulation of photosynthesis-related genes,thereby reducing photosynthesis.The differentially expressed genes were more significant in roots than in leaves,and GO enrichment was most significant in the extracellular region of cytological components.Biological processes included cell wall tissue or biogenesis,secondary metabolic processes,flavonoid biosynthesis and other metabolic processes,and molecular functions included transferase activity and monooxygenase activity.7.KEGG enrichment results showed that 2,388 and 4,527 unigenes were annotated for BLI-vs-BL10 and BG1-vs-BG10,among which 1,212 and 2,974 unigenes were up-regulated and 1176 and 1553 unigenes were down-regulated,respectively.The number of corresponding genes in leaves was relatively small.The KEGG metabolic pathways of root and leaf differentially expressed genes were divided into 7 pathways,including substance metabolism,cell process and environmental information processing,and were involved in 33 metabolic pathways.Substantial metabolism includes carbohydrate metabolism,amino acid metabolism,energy metabolism,and biosynthesis of other secondary metabolites.Cell processes include transport and catabolism,cell growth and death,etc.Environmental information processing focuses on signal transduction.Under drought stress,there were significant differences in gene expression between root and leaf of Camellia oleifera,among which the biosynthesis of flavonoids showed the most significant difference,indicating that flavonoids played an important role in response to drought stress.In conclusion,the external morphology,physiological and biochemical characteristics and internal gene expression of Camellia oleiformis are responsive to drought stress.With the intensification of drought stress,the differentially expressed genes were significantly enriched in photosynthesis,osmoregulation substances,secondary metabolites,signal transduction and other pathways,especially in the flavonoid synthesis pathway. |
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