| Today,more than 20% of the world's cultivated land is threatened by different degrees of salinization.Salt stress has become an important factor affecting crop and food production worldwide.Starch is the main storage form of carbohydrate in plants,and environmental changes can affect the starch synthesis process in plants.Many studies have proved that the starch and soluble sugar content of plants will be affected by salt stress.Meanwhile the expression of related genes and activity of enzymes will respond to stress.We analyzed transcriptome of two soybean breeds under salt stress and study gene function in mutant of rice.We hope we can explain the difference of starch accumulation and two soybean breeds.The main results are as follows:(1)Salt treatment accelerated starch accumulation in soybean leaves.Through iodine staining of leaves and electron micrographs of chloroplast in mesophyll cells,we found that the accumulation of starch has no difference between two breeds.However,a significant difference in the numbers and size of starch granules in chloroplast was found under salt stress.S111-9 showed less starch granules number and smaller starch granules size than Melrose with 4 hours treatment of 150 mM salt stress.But the difference became smaller with 2 days treatment.This indicated that the starch accumulation of S111-9 was slow under salt stress.(2)Transcriptome analysis showed that the gene expression of different salt tolerant materials was different after salt stress.We analyzed transcriptome of soybean after salt stress and found that S111-9 had more different expressed genes than Melrose.The results of GO enrichment showed that the differentially expressed genes of the two breeds were mainly involved in the process of protein phosphorylation and oxidation-reduction process under salt stress.And DEGs between treatment groups were mainly involved in oxidation-reduction process.The results of KEGG enrichment showed that the differentially expressed genes were mainly enriched in plant hormone signal transduction,MAPK signal pathway-plant and starch and sucrose metabolism.DEGs between treatment groups were mainly enriched in phenylpropanoid biosynthesis and plant hormone signal transduction.In the plant hormone signal transduction pathway,GA signaling pathway showed different up and down-regulation trends in the two breeds.Most of the genes involved in MAPK signaling pathway-plant were differentilally expressed only in S111-9.In starch synthesis pathway,most genes were down regulated under salt stress,but one GBSS gene was up regulated under salt stress.The expression of one PGI gene showed different change between two breeds.In the process of starch degradation,most of the genes were up regulated under salt stress,and the up-regulated degree of these genes of S111-9 was higher than that of Melrose.And the analysis of some plastic membrane located transporters showed that one GPT2 gene was down-regulated in Melrose and up-regulated in S111-9.The different expression of genes in these pathways may be one of the reasons that can explain the difference of starch accumulation and salt tolerance between two breeds.The expression of major genes in starch synthesis was confirmed by qRT-PCR.Most of the changes in gene expression were consistent with the transcriptome data.(3)PGI gene knockout mutant influenced starch accumulation in chloroplast.We used CRISPR-Cas9 technology to get PGI gene knockout mutant in rice.The weight of 1000 seeds of mutant was lighter than that of wild type.The seed endosperm of mutant was white,opaque and powdery.The seedling was short,and the edge of leaf was white.The accumulation of starch in leaves decreased,and there were almost no starch grains in chloroplasts.It indicated that PGI gene was important in starch accumulation in plants. |
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