| In the context of global climate change,an increasingly significant role water restrictions on desert region,vegetation recovery more difficult,and with the global nitrogen deposition rate increased in recent years,the influence of the change of the nutrient content of plant will be increasingly significant,therefore,for the arid and semi-arid regions,study plant nutrient content and the increase of drought stress has the vital significance.Nitraria tangutorum is a common building species and sand-fixing species in desert areas,with super drought,salt and alkali resistance characteristics.At present,the reproduction,photosynthetic characteristics and other aspects of N.tangutorum have been clarified,however,under the condition of nitrogen increase and worsening drought,N.tangutorum growth and physiological characteristics of endogenous hormone levels change mechanism is unclear,due to the lack of genetic information,N.tangutorum molecular mechanism of nitrogen added and drought stress response need to be researched.in this study,different nitrogen addition and drought stress tests were conducted to look for the response rules of growth and endogenous hormone content of N.tangutorum,and the leaf transcriptome comparative analysis was conducted to explore the molecular mechanism of N.tangutorum 's response to nitrogen addition and drought stress.It provides a theoretical basis for revealing the growth regulation mechanism of desert and xerophytic plants and cultivating new varieties resistant to stress,as well as for the sustainable development of desert ecosystem.The main results are as follows:1.N.tangutorum plant height,leaf length,leaf width,SLA,LDMC,root biomass,leaf biomass,stem biomass and overall plant biomass all reached the optimal growth state when nitrogen concentration was 36 mmol·L-1;at a soil moisture content of 60-80%,leaf width,specific leaf area,dry matter content,plant height,nodule length and leaf number,root biomass,branch biomass and total biomass all reached the maximum,the soil moisture content of 60%-80%becomes the best water niche for the growth of N.tangutorum;nitrogen addition and drought stress had significant positive interaction effect on root growth of N.tangutorum2.Under normal water supply conditions,the contents of IAA,ABA,GA and SA first increased and then decreased with the increase of nitrogen addition.When nitrogen addition concentration was 36 mmol·L-1,ABA,SA and JA significantly increased and reached the maximum value;under drought stress,the contents of IAA,ABA and GA were significantly increased by nitrogen addition,while SA and JA were significantly decreased,nitrogen addition and drought stress had positive interaction with endogenous ABA,GA,SA and JA contents in N.tangutorum.3.In this study,RNA-seq technology was used for the first time to sequence the transcriptome of the leaves of N.tangutorum,89.67G of data was obtained,332,420 transcripts and 276,423 Unigene were obtained after the do novo assembly.The number of DEGs obtained in different nitrogen addition samples were respectively:N0vsN6 has 4,052 DEGs,including 1,482 up-regulated genes and 2,570 down-regulated genes;N0vsN36 contained 6,181 DEGs,including 1,687 up-regulated genes and 4,494 down-regulated genes;N0vsN60 has 3,937 DEGs,including 2,042 up-regulated genes and 1,895 down-regulated genes.The number of DEGs under drought stress was 10,229,including 4,767 up-regulated genes and 5,462 down-regulated genes.The DEGs were mainly associated with heme binding,peroxidase,hydrolase,oxidoreductase and dehydrogenase.The expression results of 20 genes detected by real-time fluorescence quantitative PCR were consistent with those obtained by high-throughput sequencing.4.The GO function enrichment of N0vsN6,N0vsN36 and N0vsN60 showed that 2412,4078 and 2482 DEGs were annotated by GO,The significantly enriched GO term was mainly related to chitinase activity,oxidoreductase activity,hydrolase activity,cell wall macromolecule catabolic process,amino acid synthesis and metabolism,organonitrogen compound biosynthetic process,hormone metabolism and chlorophyll metabolic process;N0vsN6,N0vsN36 and N0vsN60 were 1101,2222 and 1234 DEGs annotated into 113,121 and 114 classified metabolic pathways in KEGG database.The metabolic pathways of significant enrichment mainly involve anthocyanin biosynthesis,carotenoid biosynthesis,porphyrin and chlorophyll metabolism,flavonoid biosynthesis,taurine and hypotaurine metabolism,photosynthesis-antenna protein,glutathione metabolism,fatty acid degradation,amino acid metabolism and other processes.Under drought stress,3,849 DEGs were mainly enriched to cellulose biosynthetic and metabolic process,chitin catabolic process,amino sugar catabolic process,and response to water by GO.3047 DEGs annotation to KEGG database 119 classification metabolic pathways,significantly enriched access mainly relates to the ribosome,plant hormone signal transduction,protein processing in endoplasmic reticulum,porphyrin and chlorophyll metabolism,spliceosome,phenylalanine,tyrosine and tryptophan biosynthesis,starch and sucrose metabolism,anthocyanin biosynthesis,flavonoids biosynthesis,photosynthesis-antenna proteins.5.Porphyrin and chlorophyll metabolism were involved in molecular regulation in response to nitrogen addition and drought stress.The gene expressions of NR,GS,NADH-GOGAT and Fd-GOGAT in the nitrogen metabolism pathway were all changed,and they coordinated with each other to participate in the positive regulation in response to drought stress.Under drought stress,the signal transduction of the hormones CTK,ABA,ET and BR was activated,and the signal transduction of IAA,GA,SA and JA was inhibited.Under drought stress,496 genes encoding transcription factors belonging to 58 transcription factor families were found,including 204 up-regulated genes and 292 down-regulated genes.The mechanism of signal transduction under drought stress and its important role in drought resistance were revealed. |
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