| In response to the increasing demand fornatural fibers such as cotton and hemp in the textile industry,Apocynum venetum is known as the "king of wild fibers",and it has a very broad development prospect in the textile industry.In this study,A.venetum was used as the experimental material,and the combination of physiological index determination and transcriptomics was used to carry out the morphological changes of fiber cells in four main stages(Germination stage,seedling stage,enlightenment stage,fruit ripening stage)of A.venetum fiber development,the content of chemical components in hemp skin,plant agronomic traits,and fiber development.Related enzyme activities,changes in sugar content and fiber quality indicators,and then the stem materials of these four periods were used as samples for transcriptome sequencing,and the study of comparative analysis of the transcriptome of stems in different periods was carried out.To explore the molecular regulation mechanism of A.venetum fiber development process,aiming to clarify the development law of A.venetum fiber and its molecular regulation mechanism.The experimental results are as follows:(1)The results of the research at the physiological level are reflected in five terms.①In terms of morphogenesis,it was found that the fibrous cells of A.venetum began to differentiate and form when they were green and excavated,and the fibrous cells in the middle of stem before and after seedling stage belonged to the process of initiation,elongation and secondary wall thickening respectively.Fibroblasts develop in different parts in the same period,and the development is at an early stage along the growth direction.②In terms of chemical components of stem bark,it was found that with the growth and development of the same part of the stem,the contents of cellulose and lignin increased gradually,reaching 10.45%and 44.15%(middle part of the stem),respectively,while the contents of pectin and hemicellulose decreased gradually,reaching 10.69%and 15.86%(middle part of the stem).In the same period,different parts showed opposite trends along the growth direction and with the progress of development.The results showed that A venetum fiber should be harvested at fruit maturity stage or even later,and the harvested fiber contained a large number of non-cellulose substances,which was not conducive to fiber utilization.③In terms of agronomic traits,it was found that plant height,stem diameter,skin thickness,fresh stem weight,biomass,fresh tare weight,fresh stem hemp rate and other traits were significantly positively correlated with the yield of raw hemp,and there were also mutual influences between the traits.The results showed that plant height,stem thickness,bark thickness and other agronomic traits could be used to evaluate the yield of A venetum.④ In terms of physiology and biochemistry,it was found that the activities of sucrose synthase(decomposition direction),sucrose phosphate synthase,and β-1,3 glucanase had similar changing trends,showing a downward trend overall.The change trend of sucrose content and sucrose synthase(decomposition direction)activity was opposite,and the content of fructose and glucose gradually decreased,indicating that the accumulation of cellulose was rapid in the early stage of development and slowed down in the later stage.⑤In terms of quality identification,it is found that the diameter of A.venetum was 14.1 μm,which was lower than that of flax,ramie and cotton fibers,and had strong spinnability.The breaking strength is 1531.4 N/mm2,which is higher than that of flax,ramie and cotton fibers,while the elongation at break is opposite,indicating that A.venetum fibers have significant high-strength and low-elongation characteristics.In terms of fiber supramolecular structure,the crystallinity is 65.92%,which is comparable to flax,but lower than that of ramie fiber,and the orientation degree is 98.41%,but higher than both.(2)At the genetic level,comparative transcriptomic methods are used to study.①A total of 543,163,384 Clean reads were obtained by RNA-seq sequencing,accounting for 98.05%of the original sequence,and the sequencing error rate was 0.03,indicating good sequencing quality.The comparison with genome data showed that the comparison rate was more than 95.20%,indicating that the sequencing and comparison results were good.②With p-value ≤ 0.05 and |log2FoldChange |≥ 1 double standard for the filter,filter out 7723 DEGs.The number of DEGs decreased first and then increased in the combination before and after the development stage,while the number of DEGs increased gradually with the development stage as a control,and the number of DEGs showed a dynamic change process.③ GO enrichment analysis showed that the biological process Term of auxin response and hormone response was significantly enriched in the early stage of development,and the cell components Term and cell wall tissue or biological process Term of biogenesis,cell wall tissue and glucan metabolism were significantly enriched in the later stage of secondary wall thickening.④KEGG enrichment analysis showed that phenylpropane biosynthesis,starch and sucrose metabolism,and plant hormone signal transduction pathways were significantly enriched in most of the comparison groups,and 52,73,57 DEGs encoding key enzymes were screened out,respectively.(3)Screening of candidate genes for A.venetum fiber synthesis.Search for Arabidopsis thaliana orthologous genes involved in plant fiber formation in A.338 candidate genes that may be involved in fiber synthesis were screened in A.venetum.These candidate genes are involved in multiple biological processes,Respectively 23 candidate genes of fiber initiation and elongation,sitosterol biosynthesis 22 candidate genes,UDP-glucose biosynthesis 13 candidate genes,cellulose biosynthesis in 46 candidate genes,the biosynthesis of xylan five candidate genes,lignin biosynthesis of 58 mutual transformation between candidate genes,UDP-sugar 30 candidate genes,auxin biosynthesis 63 candidate genes,17 candidate genes for gibberellin biosynthesis,23 candidate genes for cytokinin biosynthesis,13 candidate genes for transcription regulation of secondary cell wall formation,and 25 candidate genes for autophagy regulation.Based on these candidate genes,combined with the morphogenesis process,established A.venetum phloem fiber development model.The reliability of RNA-seq sequencing was verified by qRT-PCR. |
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