| Sorghum [Sorghum bicolor(L.)Moench] is the fifth largest food crop in the world and is widely planted in arid and semi-arid areas.Sorghum has the characteristics of drought resistance,waterlogging resistance,saline alkali resistance and barren resistance.It plays an important role in dryland agriculture and marginal land in China.Sorghum is a successful model of utilizing heterosis.Except for planting conventional varieties in some areas,hybrids are used in most Sorghum Planting Areas in China.Although the research on the utilization of heterosis in sorghum was carried out earlier,there are few reports on the molecular mechanism of heterosis compared with rice,corn and other crops.In addition,hybrid breeding mostly depends on the experience of breeders,and the breeding efficiency is low.Therefore,clarifying the prediction method of sorghum heterosis and exploring the genetic basis of heterosis have important guiding significance for improving sorghum breeding efficiency and clarifying the mechanism of heterosis formation.In this study,21 sorghum parental lines were selected to prepare hybrid combinations,the combining ability and heterosis of various characters were analyzed,and the feasibility of combining ability and molecular genetic distance for heterosis prediction was discussed.Taking the strong heterosis combination Jinnuo NO.3 and its parents as experimental materials,combined with transcriptome and small RNA sequencing,this thesis explores the metabolic pathways and key genes involved in the formation of heterosis,and discusses the mechanism of the formation of heterosis of Jinnuo NO.3,so as to provide some new clues for the utilization of heterosis and high-yield breeding of sorghum.The results are as follows:1.Using incomplete diallel cross design(NCII),98 F1 combinations were prepared with 7 male sterile lines as female parents and 14 restorer lines as male parents.The parents and hybrid combinations were investigated for 5 characters for 2 years.The results showed that the middle parent heterosis of plant height,grain weight per panicle,panicle length and 1000 grain weight from strong to weak,and the order of high parent heterosis(HPH)and middle parent heterosis(MPH)from strong to weak was the same.The analysis of combining ability showed that there were great differences in general combining ability(GCA)and special combining ability(SCA)among different parents.Most combinations with high special combining ability have high general combining ability of their parents.Male sterile lines 10480 A,3765A and restorer lines R111,L2 R and JY15 had high combining ability and excellent comprehensive characters;Seven strong heterosis hybrid combinations were selected to provide reference for sorghum hybrid breeding.2.The genetic distance among parents was calculated based on 185,451 high-quality SNPs.The range of genetic distance among 21 parents ranged from 0.01 to 0.88,with an average of 0.45.The genetic distance between male sterile lines ranged from 0.13 to 0.71,with an average of 0.34.The genetic distance between restorers lines ranged from 0.01 to 0.58,with an average of 0.26,indicating that the restorers lines were closely related,and the genetic basis of restorers should be broadened.The genetic distance of SNP molecular markers among parents was only positively correlated with the super parent heterosis of ear length(r=0.21)and the high parent heterosis of yield(r=0.33)(P< 0.05).However,the mid parent heterosis and high parent heterosis of all traits were significantly positively correlated with GCA and SCA of their parents,indicating that in the prediction of heterosis,the combining ability of parents can effectively predict heterosis,and the prediction effect is better than molecular genetic distance.3.RNA-seq technique was used to analyze the transcriptome of young panicles of sorghum hybrid‘Jinnuo NO.3’ and its parents 10480 A and L17 R at the stage of secondary branch differentiation and spikelet differentiation,and to study the relationship between gene differential expression and heterosis.The results showed that there were 2641 and 2175 differentially expressed genes in the two stages compared with 10480 A.There were 1387 and 1094 differentially expressed genes in hybrids compared with L17 R,respectively.There were a wide range of differentially expressed genes between hybrids and parents.The analysis of gene expression patterns showed that most genes showed additive expression patterns,indicating that the complementary effect may play a basic role in Sorghum ear heterosis.In the non-additive expression genes,the super paternal expression pattern is dominant,indicating that the paternal L17 R may provide beneficial alleles that contribute to heterosis.Go and KEGG analysis showed that photosynthetic antenna protein,photosynthesis,photosynthetic carbon sequestration,amino acid metabolism,glycolysis and endoplasmic reticulum protein processing may be involved in the formation of yield heterosis of Jinnuo NO.3.Further analysis showed that the genes CB4 A and FER3 related to photosynthesis,the genes HS17 A,HSP7C,HSP21 and HS24 M related to stress resistance,and the transcription factors MADS1,MADS7,MADS16 and MADS55 related to ear structure development may play an important role in the formation of yield heterosis of Jinnuo NO.3.4.Small RNA sequencing was performed on the young panicles of Jinnuo NO.3 and its parents by high-throughput sequencing technology.After sequence assembly and functional annotation,142 expressed conserved mi RNAs were identified,and 51 and 41 differentially expressed mi RNAs between hybrids and parents were identified at the stage of secondary branch differentiation and spikelet differentiation,respectively.Among them,18 differential mi RNAs predicted 23 corresponding differentially expressed target genes,which were significantly enriched in metabolic pathways such as DNA,RNA regulation process and plant pathogen interaction.Combined with the combined analysis of m RNA differential expression,the non-additive regulated mi R156-SPL7 and mi R319-TCP pathways may be related to the heterosis of grain number per panicle and grain yield of sorghum hybrids.5、According to the results of RNA and mi RNA sequencing,it was found that the genes involved in photosynthesis,ear development and stress were up-regulated in hybrids,such as Psb W Psb R,Lhca2,Lhcb1,LAX3,MADS1,mi R156-SPL7,WRKY14,WRKY35,HSFB2 C,HSP70 and other genes,indicating that these genes play an important role in the formation of sorghum heterosis.These results provide new clues for revealing the key regulatory networks and genes of sorghum heterosis. |
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