Interspecific Differences And Altitude-adapted Physiological And Metabolic Characteristics Of Typical Acer Species In Northeast China

Acer L.comprises about 200 species worldwide which are regarded as important ornamental species for their richly coloured autumn leaves,unique winged fruits and leaf shapes,and are mostly used in natural landscapes and landscaping.Acer plants also have important utilization value in edible,medicinal and timber applications.China has the most abundant germplasm resources of Acer plants in the whole world,and the northeastern region is one of the important distribution areas of Acer plants.The potential impact of climate change on the growth and distribution of species and ecosystem structure has attracted researcher’s attention.In mountain ecosystems,environmental changes caused by altitude gradients include several factors such as temperature,precipitation,radiation,and soil physical and chemical properties,so the study of altitude acclimation can help to understand the long-term response mechanisms of plants to environmental changes.There are no systematic studies on interspecific differences in altitudinal adaptations of Acer genus at the physiological,transcriptional and metabolic levels.In this study,4 Acer species growing in Grand Canyon National Nature Reserve were used as the study target.Based on the joint multi-omics analysis techniques,the physiological characteristics,transcription factors,primary and secondary metabolites of 4 Acer species were comparatively analyzed to study the following two components:（1）interspecific physiological metabolism differences among Acer ukurunduense Trautv.et Mey.（AUT）,Acer pictum subsp.mono（Maxim.）H.Ohashi（APM）,Acer tegmentosum Maxim.（ATM）,and Acer mandshuricum Maxim.（AMM）under different horizontal distribution conditions;and（2）to reveal the altitudinal adaptation strategies of AUT under vertical distribution conditions.The main findings of our study are as follows:（1）The interspecific differences among the 4 studied Acer species at the physiological,transcriptional and metabolic levels:（a）there were significant differences in physiological metabolic processes.physiological characteristics of AUT were more correlated with POD,CAT,O^2-,portal aminotransferase,phenylalanine aminotransferase,chalcone isomerase;APM was more correlated with Na,Mg,Mn,B,glutamate dehydrogenase;ATM and AMM were more correlated with Ca,Se,Cu,Fe,soluble sugars,soluble proteins,and sucrose synthase were more correlated.（b）RNA-seq sequencing analysis of of the 4 studied Acer species revealed that the transcript level differences were mostly concentrated in the pathways of photosynthesis,glycerophospholipid metabolism,flavonoid biosynthesis,starch and sucrose metabolism,and phenylpropanoid biosynthesis.（c）At the metabolic levels,non-targeted primary metabolites and targeted phenolic compounds were measured in the 4 studied Acer species based on the transcriptomic results.68primary metabolites were detected in leaves of Acer species,and fructose was the key metabolic node in of 4 Acer species.The distribution of phenolic compounds in Acer species was distinctly interspecific,with C6C1 and C6C3 analogues accumulating more in ATM and AMM.C6C3C6 analogues accumulated more in AUT and APM,indicating that these 2 species are more resistant to stress.The results of clustering analysis revealed that APM and AMM had higher similarity at the metabolic level.（d）Coenrichment analysis of interspecies differences in genes and metabolic nodes revealed that the regulation of metabolic nodes in different Acer species was species-specific.The metabolic node in ATM is positively regulated by sedoheptulose-bisphosphatase,PFKFB3,HK,GFPT,and negatively regulated by GMDS and MAN.the metabolic node in AMM is positively regulated by GFPT,GMDS,TPI,PFK,and negatively regulated by HK,UCK,PFP,and PFKFB3 are negatively regulated.（2）Altitudinal adaptation of AUT at the physiological-metabolic level:（a）Soil properties（total nitrogen,total carbon,urease,peroxidase）and plant inclusions（total nitrogen,organic carbon,total flavonoids,soluble sugars）,mineral elements（Zn,Cu,Mn,Se,Mn）,and biological enzymes（glutamate dehydrogenase,sucrose synthase,chalcone isomerase）were correlated with the adaptation of AUT to high altitude distribution.（b）Adaptation of AUT to altitude changes is accomplished by multiple physiological activities in concert.Photosynthetic pigment and soluble sugar content rise with altitude to provide energy for plant adaptation to environmental changes.The oxidative stress system is dominated by SOD,and the mineral elements Mn,B and Cu play a synergistic role.（c）Comparative analysis of differences in AUT from different altitudes at the transcriptional levels yielded a total of 2110 altitude-adapted related genes,significantly enriched in the biosynthesis of phenylalanine analogues,flavonoid biosynthesis,starch and sucrose metabolic pathways.A total of 5 primary（glucose,galactose,glycerol,quinic acid and mangiferic acid）and 13 secondary（hesperidin,poplarin,catechin,Douglas fir,naringenin,mistletoe glucoside,soybean glucosin,genistein,apigenin,lignan,galangin,glycyrrhizin and isoglycyrrhizin）altitude-adapted key metabolites were obtained by untargeted and targeted metabolomics analysis.（d）To further understand the altitude adaptation of AUT,coenrichment analysis of key differential genes and metabolites in response to altitude change was performed.The results showed that adaptation of AUT to altitude changes was synergistically regulated by five metabolic pathways:glycolysis/gluconeogenesis,glycerolipid metabolism,galactose metabolism,biosynthesis of phenylalanine,tyrosine and tryptophan,and flavonoid biosynthesis.The glycolysis/gluconeogenesis pathway（glucose）and flavonoid biosynthesis（hesperidin,salicin,catechin,Douglas fir,naringenin and mistletoe）were positively and synergistically regulated by the genes GOLS,TPI,INV,and HCT.Galactose metabolic pathway（galactose）,phenylalanine,tyrosine and tryptophan biosynthetic pathways（quinic acid and mangiferin）are positively and synergistically regulated by genes aro K,phospholipid:diacylglycerol acyltransferase,PFK,GALM,GALM.The glycerolipid metabolic pathway（glycerol）is positively and synergistically regulated by the genes MGD,GLYK,DFR,ASP5,HCT,PGT,ANR and UGP3 were positively and synergistically regulated.The flavonoid biosynthetic pathway of soybean sapogenins,genistein,apigenin,lignan,galangin,glycyrrhizin,and isoglycyrrhizin were positively and synergistically regulated by genes DFR,GOT1 and AKR1A1.In addition,isoglycyrrhizin as an altitudinally adapted important compound was synergistically regulated by phenolic compound synthesis related genes（CHS,F3H,CHI,ANS,LAR,CYP75B1）with phosphofructokinase gene（PFP）.In summary,this study provides a comprehensive analysis of interspecific differences in altitude adaptation of Acer species from physiological,transcriptional and metabolic perspectives.The results of the study not only provide a scientific basis for exploring the metabolic-evolutionary relationships of Acer species,but also provide a research basis for scientific issues such as environmental adaptations of plants in the context of global climate change,and provide a theoretical basis for the development and utilization of Acer species resources.