Revealing The Adaptive Differentiation Between Miscanthus Lutarioriparius And Miscanthus Sacchariflorus In China

Adaptation is the most important survival and reproductive capacity that organisms need to cope with the changing environments.In the process of adapting to the environment,the adaptive evolution of organisms was shown by phenotype or genotype variations,which were impacted by a series of factors,such as natural selection,population genetic level,internal physiological and biochemical characteristics and the surrounding ecological environment.Miscanthus lutarioriparius,endemic in China and its related species Miscanthus sacchariflorus in common gardens showed a strong adaptability to various types of marginal land and the former maintained the characteristics of high biomass.Certainly,the two species have been controversial in taxonomic status.Here,we performed the scanning electron microscope and RNA-seq to detect the variation of microstructure and gene expression in full-year growth seasons.The key results and conclusions are as following.1.We used scanning electron microscope(SEM)to observe the transverse structure of the stem tip tissues of M.lutarioriparius and M.sacchariflorus.We found M.sacchariflorus is a hollow structure and M.lutarioriparius is a solid structure filled with a large number of thin-walled cells in the early stage,and a hollow structure at the end of the growth stage.The thick-walled tissue can be observed around the vascular bundle structure of M.sacchariflorus,while there is no obvious mechanical tissue in the vascular bundle of M.lutarioriparius;Under the same magnification,the number of vascular bundles of M.sacchariflorus with hollow structure is higher than that of M.lutarioriparius,but the vascular bundle aperture of M.lutarioriparius is larger.In the process of macroscopic morphological analysis,we found that the monthly average of M.lutarioriparius was 2.5 meters higher than that of M.sacchariflorus individuals,and the branching traits of M.lutarioriparius were observed from July,indicating that the biomass of M.lutarioriparius was much higher than that of M.sacchariflorus.However,the vascular bundle,as an important water nutrient drainage organ of plants,is not as abundant as M.sacchariflorus in the number of M.lutarioriparius.We hypothesized that the M.lutarioriparius vascular bundle structure with large pore diameter and no obvious mechanical structure was an efficient and advanced vascular bundle structure generated during adaptive differentiation.2.We also performed SEM to observe the leaf structure of M.lutarioriparius and M.sacchariflorus,including upper leaf surface,lower leaf surface and transverse leaf section.We found that M.lutarioriparius have the similar stomatal numbers in the upper and lower surfaces and M.sacchariflorus had less stoma on upper surfaces than in lower surfaces.There was non-significant differentiation in stomatal size between M.lutarioriparius and M.sacchariflorus.The stomatal number might increase the photosynthesis of M.lutarioriparius,which cause the species with growing high stems and the huge biomass.3.Transcriptomic sequencing was used to analyze the variation of gene expression.We obtained about 1434039996 original sequences with a length of 80 bp.After data filtering,data of 199.44 Gb were used to following analysis.We deleted the genes with an average expression level of 0.The number of expressed genes for M.lutarioriparius individuals varied from 18910 to 20653,and the number of expressed genes for M.sacchariflorus individuals varied from 20010 to 20436.Using t-test/Wilcoxon-test and fold change methods,we detected that there were 2360(16.18%)genes that were significantly up-regulated.3660(25.09%),the number of insignificant genes was 14589(58.73%)between M.sacchariflorus and M.lutarioriparius.Based on the principal component analysis there was obvious differentiation on the second principal component.We screened the top 20 contribution rate of the second principal component and found that these genes are mainly involved in the processes of plant photosynthesis,cell metabolism,defense,and signal transduction.At the same time,a quarter of the genes' functions are still unclear.All the above studies,they indicated that M.lutarioriparius differentiated from M.sacchariflorus in morphology,physiology and molecular level,and the high M.lutarioriparius biomass had strong ecological adaptability.