| Cassava?Manihot esculenta Crantz?is an important starchy crop.It plays an important role in global food security.The whole plant of cassava is valuable,which the starch rich roots are the most important part of the application.Cassava yield is high,with more than 35%of the starch content in roots,but their tuber root's shelf life is very short and perishable after harvest in comparison to other root crops.Deterioration usually begins at 1 to 3 days after harvest,which reduces the transparency and the quality of starch;affects the processing of starch and fuel ethanol;and results in huge economic losses for the enterprises and farmers.Therefore,postponing cassava block post-harvest decay and deterioration,improving its shelf life is the main goal of cassava breeding.One of the most important problems plaguing the development of cassava industry is the post-harvest metamorphism.Screening anti-postharvest deterioration of cassava germplasm is one of the ways to solve this problem.Our research team has screened a new cassava germplasm?RYG-1?with special anti postharvest physiological metamorphism during the years of cassava breeding.Compared with the conventional cassava Southern China 8?SC8?,the RYG-1 had good resistance to rot and storability.To study the cause of the strong resistance to postharvest decay and metamorphism of this new germplasm,the agronomic traits and physiological indexes were analyzed;meanwhile the differential gene expressions during the postharvest decay was detected by using transcriptome sequencing.The PPD responsive genes and the related metabolic pathways were analyzed.The results are as follows:1.Analysis of the agronomic characters in the fieldThe plant height,leaf area,stem diameter,intemode length,numbers and weight of the tuber roots,and dry matter percentage were measured.The results showed that the plant height,leaf area,internodelength,the numbers of tuber roots and weight per plant of RYG-1 are superior to the control of SC8;while the stem diameter and dry matter content of RYG-1 are lower than SC8.2.Analysis of the physiological indexesThe content of chlorophyll in RYG-1 was slightly higher than that in SC8,and the change in different growth stages was not significant.The changes of soluble sugar,soluble protein and proline were irregular in the two germplasms.The content of H2O2 in the four planting periods was small changed,but the H2O2 content in RYG-1 in was lower than SC8 as the planting time expanding?at november and December?.The activities of SOD and CAT in both germplasm were increased gradually with the prolongation of planting time,and the activities of both enzymes in RYG-l were higher than those in control SC8.All the results show that the activity of SOD and CAT couble be used as a screening index of post-harvest metamorphic cassava.3.Transcriptome sequencing analysis of two cassava germplasms of SC8 and RYG-1 before and after storageTranscriptomic sequencing analysis was performed on RYG-1 and SC8 at fresh and 3 weeks post-harvest roots.The results showed that the main components of fresh RYG-1 and SC8 PCA have little difference,while the PCA had the most significant differences in the main components after storage.The number of differentially expressed genes showed that the genetic differences between the two germplasms of SC8 and RYG-1 were little when fresh,and there were only 50 DEGs.There were more than 2440 DEGs in post-harvest differential genes.In SC8,the total number of differentially expressed genes in the tuber roots was 3459 between fresh and after storage in tuber roots.The number of up-regulated genes was 1501,and down-regulated genes was 1958.The total number of genes differentially expressed between the RYG-1 stored and fresh roots was 3,433,and the number of up-regulated genes was 1289,and the number of down-regulated genes was 2144.The GO analysis of the differential genes revealed that there were some differences in the significant GO enrichment of DEGs in response to postharvest stress by the two germplasms.The 3,459 DEGs collected in SC8 post-harvest were significantly enriched into 16,10,and 12 items under the three major categories of biological processes,cellular components,and molecular functions.The first three of biological process groupings are:metabolic processes,single biological processes,and cellular processes.The first three in the group of cell components are:membrane,cell part,and cell.The first three groups in the molecular function grouping are:substance binding,catalytic activity,and transporter activity.3343 DEGs after RYG-1 harvest were significantly enriched in 14,11 and 12 items under the three major categories of biological processes,cellular components and molecular functions.The first three of biological process groupings are:metabolic processes,cellular processes,and single biological processes.In the group of cell components,the first three are:membranes,cell parts,and cells.The first three subgroups in the molecular function group are:substance binding,catalytic activity,and nucleic acid binding transcription factor activity.There are unique GO items "Cell killing" and"reproduction" after SC8.There is a unique GO item "membrane-enclosed lumen" after RYG-1.Pathway analysis of the differential genes revealed that there were some differences in the significant enrichment of pathways of DEGs in response to postharvest stress in the two germplasms.The top three metabolic pathways involved in SC8 post-harvest DEGs were phenylpropanoid biosynthetic pathway,starch and sucrose metabolism,pathway and photosynthesis metabolic pathway.The first three metabolic pathways involved in DEGs post-harvest DEGs involvement were carbon metabolic pathway,photosynthesis metabolic pathway and phenylpropanoid biosynthesis.The pathways specifically enriched for DEGs by SC8 post-harvest are stilbene and gingerol biosynthesis associated with the metabolism of terpenoids and polyketides related to the degradation of limonene and terpene and the biosynthesis of diterpene biosynthesis and other secondary metabolites.And sulfonium biosynthesis.Specific pathways for significant enrichment of post-harvest DEGs in RYG-1 include the metabolism of porphyrins and chlorophyll associated with cofactors and vitamin metabolism;photosynthetic bio-carbon fixation and nitrogen metabolism associated with energy metabolism;alanine,aspartic acid related to amino acid metabolism Glutamate metabolism,cysteine and methionine metabolism,tryptophan metabolism;fructose and mannose metabolism associated with carbohydrate metabolism;and environmental adaptation related plant pathogen interactions.Using the Wayne plot analysis,there were 1593 DEGs co-expressed between the two germplasms compared to the control,1866 DEGs specifically expressed in SC8,and 1840 specifically expressed in RYG-1.Among the 1593 DEGs co-expressed,22 genes were up-regulated in RYG-1 and significantly down-regulated in SC8.65 genes were down-regulated after RYG-1 harvest and significantly up-regulated after SC8 harvest.4.Identification of the Parts of the differential genes by qRT-PCRSusequently,16 genes of the differentially expressed genes were identified by real-time quantitative PCR?qRT-PCR?.The result from the transcriptome sequencing was similar with qRT-PCR verification.5.Post-harvest submicroscopic analysis of cassava tuberBy analysis of semi-thin and ultrathin sections of RYG-1 and SC8 roots after harvesting and fresh,it was found that the integrity of SC8 cells after harvest was reduced,cell wall degradation was severe,and a large number of starch granules were missing.The RYG-1 harvested cells were intact,the cell wall was not degraded,and the starch granules maintained a good state.In summary,through a comprehensive analysis of two germplasm agronomic traits,physiological and biochemical indicators,transcriptome analysis and submicroscopic structure,we speculated that RYG-1 may adapt to post-harvest stress by improving its antioxidant capacity and cell wall strength.And maintain the quality of the roots. |
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