Molecular Mechanism Of Ramie Seedling Responding To Water And Nitrogen Co-Limitation

Ramie,as an important traditional economic crop in China,supplies raw materials for textile,bioremediation,biofuel,novel composites,medicine industries and so on.Water and nitrogen(N),interacted profoundly at filed,crop and molecular levels,are key factors affect ramie growth and development.Integrative agricultural regulations of water and N based on the physiological basis and characteristics of plants responding to the interacted relationship.The urgent need for insighting the molecular mechanism is arising under the situation of increasing frequency and intensity of water and N interaction,induced by climate change and diverse farming techniques.However,only few single factor experiments,treated with drought or N deficiency,have been carried out in ramie research field and little has been revealed in the water and N interaction mechanism.Therefore,a combined transcriptome and proteome analysis was conducted with different water and N treatments on ramie to study the molecular mechanism of the plant responding to water and N interaction.1.Hydroponic or soil cultured experiments were performed in previous studies,however,basic difference of ramie omics profile related to water and N responding might be induced by different culturing methods.For establishing a proper culturing system,a comparison was conducted with ramie under hydroponic culturing(HC)and soil culturing treatment(SC),taking major variety Zhongzhu NO.2as material.Plant samples were collected after 30 d of culturing and transcriptome and proteome analysis were performed with Illumina Hi Seq and LC-MS/MS platform.The results showed that:the molecular profile of ramie was changes significantly under HC compared to SC,although no obvious differences were detected in aboveground phenotypic characteristics.HC induced 6786 genes(log~2Ratio>1)and1158 proteins(HC/SC Foldchange>2 or<0.5,p<0.05)differently expressed,in which 111 proteins were annotated to involve in nitrogen compound metabolic process,peptide biosynthesis,and response to water,bioprocesses directly related to water and N metabolization.The result revealed the basic difference in water and N metabolization under different culturing method and suggested that soil cultured method should be used for better simulating of field environment.The combined omics analysis showed that 230 up-regulated and 187down-regulated DEPs were significantly correlated to DEGs involved in peroxidase activity,glycosyl hydrolase activity,antioxidant activity,and glucose and polysaccharide metabolic process.The molecular profile implied that different culturing methods induce typical glycolysis and oxidative stress responding in ramie.Further,24 genes encoding acetaldehyde dehydrogenase(Bn ALDH)were identified to specifically express in roots and play important roles in adaptation of ramie under oxidative stress by overexpressing Bn ALDH18 in Escherichia coli cells.2.Previous studies did not come to a consensus in the effects of water and N interaction on different crops and none had reported the effects on ramie.Therefore,the molecular mechanism of ramie responding to water and N deficiency stress was discussed with comparisons of four treatments in this thesis,including treatment with proper water and N condition(CK),single drought stress(Wd N),single N-deficit stress(WNd)and combined water and N deficiency stress(Wd Nd).The results showed that the ramie growth was significantly affected by drought,N-deficit and the combined stress.The number of expanded leaves and plant height were significantly decreased under stresses and the effect of drought was greater than N-deficit.Different water and N levels changed the transcriptome and proteome profile of ramie,which showed a complex regulation network and multi-level coupling models under the interaction of the two factors.After stressed by 10 d,the molecular responding factors under N deficiency showed a dependency characteristic with water conditions.The water and N interaction induced changes in photosynthesis,ethylene responding,glycolysis and N metabolism pathways and then affected the growth and development of ramie.Molecular factors involved in UGT,ATPase and carbonate dehydratase play important roles in ramie adaptation under combined water and N stresses.3.Compensatory growth characteristic is vital to improve crop production when water and N recovered from previous stresses.However,the molecular mechanism of compensatory growth of ramie was unexplored.In this study,four treatments were conducted with WrNr recovered from water and N deficiency,WrN recovered from single water deficiency,WNr recovered from single N deficiency and CK at proper water and N condition.The results showed that compensatory effects of ramie were triggered by primary stresses and the phenomenon was manifested by higher expanded leaves and plant height increment under recovered treatments than CK.The expanded leaves increment under WrNr was 8.4 times of CK and the plant height increment was 1.8 times of CK.Water and N affected ramie above-ground morphology differently.Leaf growth was preferentially enhanced by rewatering and plant height was preferentially enhanced by N recovery.Water was the main driver of ramie morphology plasticity during water and N interactions.The change of root,especially the enhanced root-hairs under drought stress,was the morphological basic for compensatory growth of ramie.The combined transcriptome and proteome analysis showed that the molecular mechanism of ramie compensatory growth under water and N interaction was constituted by three parts:signaling conduction,priming effects and energy&matter relocation,in which the signaling conduction was the triggering mechanism,the priming effects was the functioning mechanism and the energy&matter relocation was the expressing mechanism.4.Based on the study of molecular mechanism of ramie responding to water and N interaction,agricultural regulation strategies were proposed for improving ramie production.The study suggested that enhancing key organs like roots,modifying regulation pathways related to water and N,and improving molecular factors related to priming effects during repeated stresses were effective breeding strategies for better water and N synergy.The study also selected key factors and pathways as priorities in further researches,such as ALDH,UGT,ATPase,carbonate dehydratase,glycolysis and ammonia sugar metabolism.