Screening And Expression Analysis Of Ramie(Boehmeria Nivea L.) With Nitrogen Efficiency

Ramie, a kind of perennial herb of Urticaceae, is a great potential for animal feed because of its high biological yield and relatively balanced nutritional quality. Nitrogen is one of the important elements in the process of growth and development of ramie, rational use of nitrogen is an effective mean to increase the biological yield and quality. There is an urgent need to breed high nitrogen use efficiency(NUE) varieties and to understand nitrogen efficiency, physiological, biochemical and molecular mechanism among the different varies of ramie genotypes for improving NUE and reducing the waste of nitrogen fertilizer. In this study, using 30 ramie genotypes as experimental materials, screened out 2 high NUE genotypes and 1 low NUE genotype by comparison of NUE, yield, quality and made physiological, biochemical and molecular mechanism researches on them. The main results are as follows:The results of subordinate function of ordering the yield and quality characters, molecular markers and NUE of 30 ramie genotypes showed that three genotypes was low NUE, low yield, poor quality and four genotypes was high NUE, high yield, good quality. The further aim of the experiment was to study the ruminal degradation and intestinal digestion of different carbohydrate components and protein components from ramie meal. The carbohydrate content of ramie leaf was 59.21%, and 99% was degradable. 97% protein components of ramie leaf was degradable.In physiological and biochemical, high NUE genotype ramie was higher than low NUE genotype in root system volume, total roots absorbing area, actively absorbing area, but low NUE genotype had strong root activity. Correlation analysis indicated that there were significant positive relationship between NUE and root volume, actively absorbing area, root activity, total roots absorbing area. With the increase of nitrogen levels, the physiological indexes of chlorophyll, soluble sugar and protein, proline, nitrogen metabolism enzymes, fiber development enzymes increased. 15 mmol/L, 12 mmol/L and 9 mmol/L were was not significantly different by 15 physiological indexes with subordinate function in the ramie elongation. So 9 mmol/L was the optimum use level.To identify common DGEs between genotypes having differential response to N-stress. We got 1165 differentially expressed genes in T29_T vs T8_T including 505 up-regulated and 660 down-regulated genes. 1277 differentially expressed genes were found in T29_C vs T8_C including 592 up-regulated and 685 down regulated genes. Additionally, the functional annotation of differentially expressed genes mainly were kinase, transcription factors and cytochrome P450. There were 30 gene ontology(GO) categories in T29_C vs T8_C related to catalytic activity and binding-related. The main significantly enriched pathways were lysosome, glutathione metabolism and retinol metabolism. There were 24 gene ontology(GO) categories in T29_T vs T8_T related to single-organism metabolic process and oxidoreductase. The main significantly enriched pathways were carbon metabolism, biosynthesis of amino acids and phenylpropanoid biosynthesis.We compared transcriptome-wide gene expression between the high NUE and low NUE genotypes ramie under deficient-N and normal conditions to identify the molecular mechanisms contributing to ramie resilience to nitrogen deficiency. Reduced deficient-N stress reaction in high NUE genotype may result from three potential molecular mechanisms. High NUE genotype had higher expression under control condition across 94 of these genes including frotloaded genes such as GDSL esterase/lipase, Gibberellin, UDP-glycosyltransferase, Omega-6 fatty acid desaturase. 17 ‘stress-tolerance’ genes showed lower expression levels and had little change in response to deficient-N stress in high NUE genotype. 170 ‘relatively up-regulated’ genes responded relatively high expression to deficient-N stress in high NUE genotype and showed down-regulated in low NUE genotype. We propose that the three classes genes enable an individual to maintain physiological resilience under deficient-N stress. These concepts could provide further insight into the mechanism link between the three classes genes and the enhanced resilience of the high NUE genotype.