Invasion Mechanism Of Flaveria Bidentis(L.)Kuntze Based On Phenotypic Plasticity And Chloroplast Genome Analysis

Flaveria bidentis?L.?Kuntze,a C₄ dicotyledon plant,belongs to genus Flaveria in the Composita family,is an alien weed of invading China.Despite the time period of invasion,it has caused serious harm to the ecological environment and agricultural production of the invaded areas by spread rapidly.Recently,the study of chloroplast genome and phenotypic plasticity has become a hot topic in plant research,especially in exploring the genomics and invasion mechanism of invasive plants.By studying the phenotypic plasticity under different salt and shading treatments,and observing the changes of growth characteristics and physiological characteristics under different habitats,we try to investigate several invasion mechanism of F.bidentis.The chloroplast genome of F.bidentis and non-invasive plants?Flaveria linearis?C₃-C₄??were compared.The mechanism of invading and adapting to heterogeneous environments of F.bidentis was discussed on morphology,physiology and comparative genomics aspects,so as to provide theoretical basis for the prevention and control of F.bidentis.The main results are as follows:?1?Complete chloroplast genome sequences of F.bidentis?Zhengzhou,Henan Province?,F.bidentis?Bolivia?and Flaveria linearis?Turks and Caicos Island?were obtained by high-throughput sequencing.Phylogenetic analysis showed that the genus Flaveria,as an independent clade,belonged to the Heliantheae alliance as well as the Heliantheae Cass and Eupatorieae Cass,but support no classification evidence for attributing Flaveria into the the tribe Heliantheae Cass.It also provided information for the genetic differentiation of Flaveria.It provides a sequence for the phylogenetic genomics of Flaveria.?2?The similarity of two chloroplast genomes of F.bidentis was more than99.99%,and most of the differences were distributed in the intergenic region.Only two different SSRs and one positive repeat were found.There was no obvious variation and differentiation,which show that be F.bidentis has strong adaptability.The overall similarity between F.bidentis?Zhengzhou??C₄?and F.linearis?C₃-C₄?was99.20%,which were significant differences in SSRs and repeat sequences,and there were 50 genes with bases changes,there are 28 genes with different codons.Among28 genes,including 8 genes related to transcription and translation and 12 genes related to photosynthesis,which may be related to the C₄ photosynthetic pathway of F.bidentis.These sequences provide important information for identifying invasive genes in chloroplast genome of F.bidentis.It enriches the genomic information of F.bidentis and provides a basis for revealing the molecular mechanism of invasiveness at the genomic level.?3?The effects of NaCl treatment on physiological,biochemical and photosynthetic characteristics of F.bidentis were studied.We found that most of the indicators did not change significantly when treated with 0.1 mol/L NaCl compared with CK.Moderate NaCl?0.2-0.3 mol/L?stress significantly inhibited the growth of F.bidentis.High concentration NaCl treatment?0.4-0.5 mol/L?breaked the homeostasis of F.bidentis and severely inhibited the growth of F.bidentis.We also calculated that the salt tolerance threshold of F.bidentis was 317.03 mmol/L,the lethal concentration was 400-500 mmol/L.The phenotypic plasticity index of F.bidentis varied from 0.17to 0.89,which indicated that F.bidentis could adapt to salt treatment by adjusting its growth physiology and other indicators.The results showed that F.bidentis had strong salt tolerance.?4?Under shading treatment,50%shading had no significant effect on the growth of F.bidentis;75%shading significantly inhibited its growth,but the seedlings of F.bidentis at the later stage of the experiment might adapt to this degree of shading;90%of the seedlings has seriously inhibited its growth,but still carry out photosynthesis.There was no"noon break"phenomenon of F.bidentis.With the increase of shading degree,LCP and LSP of F.bidentis decreased,but the apparent quantum efficiency showed a downward trend,and the difference was significant compared with the CK?P<0.05?.The variation range of phenotypic plasticity index under different shading ranged from 0.27 to 0.98.The results showed that it could adapt to different shading treatments by regulating its growth,physiological and photosynthetic phenotypic plasticity.The results showed that F.bidentis has strong negative tolerance.?5?The response of F.bidentis to different salt and shading treatments was studied.We found that F.bidentis can adapt to the environment by changing plant size,biomass distribution,leaf size and thickness,changing chlorophyll content,affecting photosynthetic rate and fluorescence parameters,and enhancing its own enzymatic activity.It shows that F.bidentis has high phenotypic plasticity,which can also maintain the necessary growth under stress.So F.bidentis has strong tolerance,which enlarges the ecological range.These factors enhance the competitiveness and invasiveness of F.bidentis,and have a strong"intrinsic advantage",which may be an important mechanism for F.bidentis to adapt quickly to heterogeneous habitats and invasive successfully.At the same time,the chloroplast genome sequences of invasive plant F.bidentis?C₄?and non-invasive plant F.linearis?C₃-C₄?were compared,we found that most of their differentially expressed genes were related to photosynthesis,suggesting that the rapid invasion of F.bidentis was related to its role as a C₄ plant.