| Plant polyploidy is normally occurred in angiosperms and plays an important role in plant evolution.Newly formed polyploids may experience short-term adaptation changes in the genome due to gene duplication,which may enhance plant resistance to stress.Drought is an crucial effect for crop failure,and will have a serious impact on the global ecosystem.To cope with the unavoidable drought problem,it is necessary to improve and innovate breeding methods to reduce the harmful effects of drought on plants.By doubling the tetraploid material "4-Alamo" swichgrass(Panicum virgatum L.)with colchicine,our team created a stable octoploid "8-Alamo",and found that octoploid material had higher drought tolerance than the tetraploid.In order to explore the molecular mechanism of Octoploid material and provide experimental basis for short-term adaptability of polyploid and drought-resistant plant breeding,this experiment was conducted on 4-Alamo and 8-Alamo materials.Four drought treatments at different time points were carried out to determine the relative water content of leaves,and transcriptome sequencing and micro RNAs sequencing were conducted to explore the molecular mechanism of drought resistance enhancement after doubling.The main results are as follows:1.Verification of stronger drought tolerance in octoploidAfter measuring the relative water content(RWC)of flag leaves(0,3,6,9 days after drought)on both polyploidy switchgrasses,the leaf RWC in octoploids was significantly higher than that in tetraploids under drought condition,and that indicated the stronger drought tolerance of octoploid.2.Micro RNAs of tetraploid and octoploid switchgrass under drought degreesEighteen micro RNA libraries were constructed and 69 conservative micro RNAs were obtained,of which 33 differentially expressed micro RNAs.Among them,sbi-micro RNA399 b was only expressed in octoploid.Five micro RNAs responded to polyploidy and three micro RNAs participated in both octoploid drought response and polyploid response.3.Transcriptome analysis of tetraploids and octoploids switchgrass under drought conditionsBy transcriptome sequencing,we sequenced 10 groups of samples(3 biological repeats of each group)from 4 time points and 1 growth control of the two polyploids.A total of132,249 different transcripts were obtained by expression calculation,and 44,416 differential expression transcripts(DETs)were obtained by differential expression analysis,annotated to 44 secondary GO biological functions.Octoploid had 23.59% more DETs than tetraploid,and it was uniquely annotated with metallochaperone activity.GO annotation of the two polyploids DETs were enriched in photosynthesis-related functions,additionally,octoploid was significantly enriched in cationic transport-related biological functions.Two ploidy switchgrasses shared 127 same KEGG pathways and had their own one unique KEGG pathway,and the most abundant pathways were photosynthesis-related pathways.After weighted gene co-expression network analysis,16 different gene expression modules were obtained.One drought response module,one ploidy response module and two polyploidydrought response modules were found.Tetraploid switchgrass adapted to drought stress mainly through consuming self-nutrition,while the octoploid maintained drought-related reactions by increasing ion transport efficiency to enhance oxidation energy supply.4.Combination analysis of micro RNAs and their target genesBy predicting the target genes of micro RNAs and analyzing them jointly,it was found that the target genes of five micro RNAs responding to ploidy changes were involved in metabolic processes.Micro RNAs differentially expressed in response to both ploidy and octoploid drought adaption are expressed in cytochrome,protein kinase and superoxide dismutase genes.5.Analysis of drought response pathwaysDifferential gene expression was analyzed from osmotic regulation pathway and chloroplast retrograde signaling pathway.Because of the different expression levels of Sn RK protein kinase and SLAC in the two types of switchgrass,the drought tolerance was affected in the downstream of response pathways.During octoploid response to drought,the high expression of oxidative phosphorylation-related genes ensures intracellular energy supply,ion balance and cell homeostasis. |
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