| The atmosphere CO2 increased sharply in recent years. The effects of CO2 enrichment on plant growth have also shown a trend of increase. D. angustifolia is the dominant species in the Sanjiang Plain. The response of elevated CO2 of D. angustifolia plays an important role in cabon cycle of vegetation system in wetland of the Sanjiang. This study focuses on the photosynthetic characteristics and anatomical structure under different CO2 concentration to investigate the effects of high CO2 concentration on photosynthesis of D. angustifolia. In this study, two sequencing libraries prepared from the control(AC) and high CO2 concentration-treated(EC2) leaf tissue samples were sequenced using Illumina sequencing technology to obtain the transcriptome information of D. angustifolia and to investigate changes in the transcriptome of the species in response to elevated CO2 concentration. Based on the gene expression patterns which involved in photosynthesis, possible roles in enhancing photosynthetic capacity played in elevated CO2-treated D. angustifolia were discussed. The results of this study are as follow:1.The obvious effect occurred in photosynthetic ability when D. angustifolia exposed to elevated CO2. Within short treaded time, the net photosynthetic rate increased with the elevated CO2. However, the net photosynthetic rate reduced, even lower than control for long exposed time. Photosynthetic acclimation phenomena occurred when D. angustifolia exposed to elevated CO2 for about 45 days. The stomatal conductance(Gs) decreased under elevated CO2. When the CO2 concentration elevated higher, the Gs decreased more, the time that Gs showed significant difference was shorter. Elevated CO2 also had significant effects on the transpiration rate of leaf. The change tendency of transpiration rate and stomatal conductance were consistent.2. D. angustifolia has obvious characteristics of C4 plant anatomy. The blade thickness which located in the main vein and between the main vein and lateral veins, the areas of sclerechyma, vascular bundle and bundle sheath cells had been influenced at different levels under elevated CO2 both in the tender and mature leaves. The thicknesses of blade and the area of vascular bundle increased under elevated CO2. However the areas of sclerechyma and bundle sheath cells showed a significant linear positive correlation with the thickness of blade which located between main and lateral veins, and were not directly influence by CO2 concentration. The five indexes of mature leaf about anatomic structure all increased under elevated CO2, however, they showed downtrend in different degrees when D. angustifolia exposed to elevated CO2 for long time.3. Using de novo assembly, 54,605 unigenes were indentified from AC transcriptome and 46,354 unigenes were indentified from EC2. 80,215 All-Unigenes were obtained by combining AC- and EC2-clean reads after removal of redundancy.4. 49,094 of 80,215 Unigenes were annotation by BLAST hits in the public databases. Among them, 39,747 Unigenes were classified into 61 GO terms, 12,484 Unigenes were categorized into 25 Clusters of COG families, and 9,732 Unigenes were assigned to 193 biochemical pathways in KEGG.5. A total of 73,301 DEGs were detected between AC and EC2 libraries though gene expression annotation and expression pattern of the differentially expressed genes. And 40,527 were up-regulated and 32,334 were down-regulated relative to the D. angustifolia under atmosphere CO2. 4,569 DEGs were identified, including 2,778 up-regulated and 1,791 down-regulated genes relative to AC. Of the total, 4,109 DEGs were annotated function, may be specific gene resource of D. angustifolia.6. 3,741 DEGs were enriched in 58 GO terms. The GO term for ‘translation regulator activity’, ‘membrane-enclosed lumen’, ‘organelle part’, ‘nucleic acid binding transcription factor activity’, ‘channel regulator activity’ and ‘protein binding transcription factor activity’ were enriched most, and close correlated with elevated CO2. 1,213 DEGs were enriched in 105 metabolic pathways. Among the pathways, ‘photosynthesis’, ‘photosynthesis- antenna proteins’ and ‘photosynthetic carbon fixation’ were activation, showed an important effect on responding to elevated CO2 in D. angustifolia.7. Respectively, 86, 34 and 125 genes among the Unigenes were identified relating to regulation of ‘photosynthesis’, ‘photosynthesis- antenna proteins’ and ‘photosynthetic carbon fixation’. Among them, 62 genes directly participated light reaction and dark reaction. The VTE3 gene had effects on light reaction indirectly, and it was inferred that the changed expression effected the content of PQ which participated photosynthetic electron transport. The expression patterns may be effected by elevated CO2.8. Under elevated CO2, the genes expressions of encoding pigment protein were up-regulated. The increasing pigment protein contents enhanced chlorophyll content. When the expression of OEC was down-regulated, more high-energy electrons were produced, and were prepared for the following electron transport. The expression of VTE3 increased, caused the raise of PQ content, and transferred more high-energy electrons and provided enough energy to dark reaction for fixing CO2. The variation of coordinate expressions of key enzymes in photosynthetic carbon fixation enhanced the carbon fixation capacity, accordingly promoted the photosynthetic rate of D. angustifolia. |
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