| Populus spp., one kind of wide spreaded broadleaf tree speices in the world, played an important role in the plantation, wood production and soil protection in China. However, companied with the huge emission of CO2 and other greenhouse gases, high temperature and drought had become the major characteristic of the world climate. Induced by the high temperature, drought and other factors, poplar canker disease(a kind of water related trees diseases that caused by fungal pathogen) is becoming the most serious poplar disease in China forest. In this study, we studied the hydraulic characteristics, soluable sugar of root and stem xylem and phloem, gene expression patterns of PIP(plasma membrane intrinsic protein)gene family of one-year-old poplar trees that infected by Botryosphaeria dothidea, and then we also analyzed the whole genome-wide gene expression patterns of infected poplars by high-throught sequencing to reveal the relation between the development of poplar canker and changes of hydraulic characteristics. The main results as follows:1. The hydraulic characteristic of poplar tree infected by canker disease pathogen: The analysis of percentage loss of conductivity of stem(PLC) showed that the water transport function of poplar decreased at the beginning of treatment of Botryosphaeria dothidea and with time passing, the function recovered gradually.Under the infection of Botryosphaeria dothidea the leaf water potential reduced significantly and the water potential of top of stem increased during the initial stage after three and five days of infection. The preliminary study indicated that inculation of Botryosphaeria dothidea would not change the osmotic potential of xylem and phloem of stem and osmotic potential of root significantly.2. The content of soluble sugar and starch of xylem and phloem of poplar: The results showed that inoculation of Botryosphaeria dothidea had no notable influence on the content of soluble sugar of xylem of stem, other than increasing that of phloem. The reason that the content of starch of xylem, phloem and root decreased under infection of Botryosphaeria dothidea is unknown. Furthermore the results also revealed the vertical distribution phenomenon of soluble sugar in xylem and phloem tissues of stem.3. In order to analyse the expression pattern of PIP genes in xylem and phloem, real-time quantitative reverse transcription polymerase chain reaction(RT-q PCR) was used.The results showed that the PIP gene family of xylem of poplar presented integral down-regulation, while a few of them significantly upregulated at special time. For example, PIP1;5,PIP2;4 and PIP2;8 upregulated on the eleventh day and the expression level of PIP2;8 was thirteen times of non-inoculated plants’.The expression characteristics of PIP genes in phloem were different from those of xylem. Some of PIP genes are suppressed to express like gene PIP1;1, some are induced to express like gene PIP1;2 on the third day after inoculation. All the twelve PIP genes were suppressed to express after seven days of infection.The expression level of PIP2;8 was only 22% of non-inoculated plants’.Most of the genes were induced by Botryosphaeria dothidea after eleven days of infection, especially gene PIP2;2,the expression level of which was seven times of non-inoculated plants.4. Under the interaction of drought and Botryosphaeria dothidea, the establishment of detection system of gene expression in poplar trees’ stem and the expression of active gene of aquaporins: Analyzing the expression stability of poplar housekeeping genes, we found that different housekeeping genes had different stabilities and TUB、UBQ、EIF4β-L、CYP、EF1α2 were the top 5 stable reference genes, while ACT2 and ACT11 were the least stable genes; Pairwise variation of expression stability analysis revealed that TUB、EIF4β-L and UBQ would be the ideal internal control for multiple-reference gene normalization; Because the expression patterns of poplar PIP genes response to fungal pathogen was not similar to which response to drought stress, the results revealed that the difference between these two kinds of stresses, drought and pathogen. The expression of 5 PIP genes(PIP1;1 、 PIP1;3 、 PIP1;5 、 PIP2;4 、 PIP2;7) in drought-pathogen interaction were higher than those in drought or infected by pathogen suggesting that there were some synergistic effects among these two environmental stresses.5. High-throught transcriptome sequencing(Hi Seq2500) was used to detect the whole genome wide gene expression in fungal pathogen infected poplar xylem and phloem samples after three days of inoculation. We derived over more than 17,919,220 Uniq Mapped reads, 206,508 SNP sites and 3981 alternative splicing sites from 1 of 4 c DNA libraries. And 104 new genes(75 among those genes had been annotated) were detected in all samples. Bioinformative analysis revealed that and 618 of 1042 differiental expressed genes up expressed in poplar phloem samples that infected by fungal pathogen, while 815 of 2382 differiental expressed genes up expressed in poplar xylem samples. The GO analysis of differiental expressed genes revealed that the physiology of poplar canker disease were highly related to the activity of glucan exo-1,3-beta-glucosidase, beta-L-arabinosidase, moreover, KEGG analysis showed that the infection of fungal pathogen induced the gene expression related to the plant-pathogen interaction and photosynthesis pathway. |
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