Characteristics Of Sucrose Accumulation And Screening Of Key Metabolism Genes In Sorghum Bicolor (L.)

Sorghum bicolor(L.)is one of the five major gramineous crops in the world.It has rich germplasm resources.Grain sorghums are rich in starch content,and sweet sorghum are rich in sugar in their stalks,which provides a resource basis for its development and utilization.Sucrose is a product of photosynthesis.It is not only the material basis for plant growth and development,but also as a signal molecule in response to adversity stress.Therefore,sucrose synthesis,degradation and transport play key roles in the growth and development of plants.Studies have shown that the enzymes involved in sucrose synthesis and degradation mainly include sucrose phosphate synthase,sucrose phosphate phosphatase,sucrose synthase,and invertase;protein families related to sugar transport include SUT,SWEET and MST families.In this study,two varieties,’BTx623’ and ’Tian C-H’.were used to study the changes of sucrose and total sugar in various tissues during different growth and development stages.Based on the whole genome sequence of sorghum,genes related to sucrose synthesis,degradation and sugar transport were selected using bioinformatics analysis.Then,the gene structure,gene expression pattern,protein conserved domain,conserved motif,genetic evolution,protein subcellular localization,heterologous function verification,were analyzed.Correlation between sorghum sugar metabolism and transport-related genes and sucrose accumulation,lays foundation for further research on the functions of sorghum sugar metabolism and transport-related proteins.The main findings are as follows:1.The variation of sucrose content in sorghum showed obvious variety and tissue diversity.The sucrose content in the leaves of BTx623 was the highest at 25 d after pollination,the sucrose content in the veins and sheaves was the highest at the elongation stage,the sucrose content in the stalks at 5 d after pollination,and the sucrose content in the grains at 10 d after pollination.The change rule of sucrose in each tissue of Tian C-H is basically similar to that of BTx623,except that the sucrose accumulation in stem is the highest,and the accumulation rate of sucrose in stem is the fastest from heading stage to 5 days after pollination.The sucrose content of BTx623 in leaves,veins,sheaths and stalks was positively correlated with total sugar.There was a significant positive correlation between sucrose and total sugar in leaves and grains,and a very significant positive correlation between Tian C-H and stem.The correlation analysis of sucrose and total sugar in leaf,vein,leaf sheath,stem and spikelet/seed at the same period showed that Tian C-H was significantly positively correlated at five time points after pollination,but not at jointing and heading stage.BTx623 showed a significant positive correlation between sucrose content and total sugar content at jointing stage,heading stage,5 d,15 d and 25 d after pollination.2.Through BLASTP homology analysis,a total of 32 sucrose metabolism-related genes from 6 families were identified in the whole sorghum genome.It contains 5 SPs(Sucrose-Phosphate Synthase),3 SPP(Sucrose-Phosphate Phosphatase),5 SUS(Sucrose Synthase),and 7 CIN(Cytoplasmic Invertase),11 CWIN(Cell Wall Invertase)and 1 VIN(Vacuolar Invertase)family members.A total of 98 sugar transporters were identified in 3 families.There were 6 SUT(Sucrose Transporter),23 SWEET(Sugars Will Eventually be Exported Transporter)and 69 MST(Monosaccharide)A member of the Transporter family.3.Sequence analysis of the genes encoding sucrose metabolism and sugar transporters showed similar or identical intron-exon distribution structures within each family.The protein characteristics showed that the S6PP domain was the conserved domain shared by SbSPS and SbSPP,Sucrose＿synth and Glycos＿tr＿1 were the conserved domain shared by SbSPS and SbSUS,and both SbCWIN and SbVIN contained Glyco＿32.The SbCIN family contains a special Glyco＿hydro＿100 domain.Sugar＿tr is a domain shared by both SbSUT and SbMST families.SbSWEET contains two MtN3＿slv domains,and sugar transporters all contain transmembrane domains,but the number and distribution of these domains are different.4.RNA-sequence analysis showed that 122 genes were expressed in different tissues,and there were differences in expression patterns among members of the same family.For example,the expression level of SbSUS1 was the highest in stem at jointing stage,while the expression level of SbSUS4 was higher in leaf,vein,sheath and stem.5.Correlation analysis between gene expression and sugar content showed that the relative expression levels of 14 genes were significantly positively correlated with sucrose content.SbSPS1,SbSPS2,SbSWEET18 and SbSUT1 were significantly positively correlated with sucrose content in leaves,SbSPS4 was significantly positively correlated with sucrose content in grains,and the expressions of SbSPS2 and SbSWEET11 in veins and sheath were significantly positively correlated with sucrose content.SbSGB2,SbTMT1,SbSPS4,SbSWEET11,SbPLT20,SbSUS1 and SbSWEET14 were significantly positively correlated with the sucrose content in leaves,veins,sheaves,stems and grains at the same period.6.Subcellular localization of onion epidermal cells and protoplasts showed that SbSWEET11,SbPLT3 and SbSTP3 were localized to the cytoplasmic membrane,while SbSWEET18 and SbGLT1 were localized to the specific membrane organelle membrane.SbSWEET15,SbPLT5,SbERD3 and SbINT3 were localized in the cytoplasmic membrane and membrane organelle membrane,while SbTMT2 was localized in the vacuolar membrane.SbSWEET11 and SbSWEET18 have galactose transporter activity,SbPLT5,SbPLT6,SbTMT2 and SbSGB2 can transport fructose in the yeast system,and SbGLT1,SbSTP8 and SbSTP9 can transport glucose.SbINT3 can transport glucose and mannitol,and SbERD3 can transport glucose and galactose.