| Sorghum grain pericarp thickness is an important factor affecting the brewing process and quality of sauce-flavored Baijiu.It not only determines the cooking resistance of sorghum,but also affects the yield of Baijiu.However,incomplete understanding of the population genetics and domestication history limits its broad applications,especially the lack of genetics knowledge underlying liquor-brewing properties makes it difficult to establish scientific standards for sorghum breeding.In this study,a population of 244 recombinant inbred lines(RILs)was constructed by crossing varieties 654 and LTR108,which had significant differences in pericarprelated traits.BSA-seq and genetic mapping were carried out in order to identify QTL/gene for pericarp thickness-related traits,and candidate genes controlling mesocarp thickness were preliminarily determined.The main results are as follows:1.Seven pericarp-related traits were investigated for 244 RILs across two years,and the results showed that the absolute values of skewness and kurtosis of exocarp,mesocarp,testa,and hulk thickness were all less than 1,indicating a continuous normal distribution and typical quantitative traits.2.Correlation analysis between different traits showed that there was a highly significant negative correlation between exocarp color and thickness of mesocarp,exocarp,and total pericarp.The mesocarp thickness was highly positively correlated with thickness of pericarp and husk,indicating that the thickness of mesocarp is the main factor affecting the thickness of husk.3.Using BSA-seq analysis,a total of 2.57 M SNPs and 0.57 M Indels were detected between two parents and a mixed pool,and important QTL loci affecting mesocarp thickness were mapped to 57.20-58.11 Mb,which is consistent with the reported location of the Z gene for mesocarp thickness and exocarp luster.4.Using QTL mapping,a total of 25 QTLs for 7 pericarp traits were identified,including 4 for exocarp thickness,4 for mesocarp thickness,3 for pericarp thickness,3for testa thickness,4 for husk thickness,2 for exocarp color,and 2 for testa color.15 unique QTL loci on 7 chromosomes were involved,of which an important locus on chromosome 2(57.83-57.96 Mb)contained 7 QTLs,consistent with the BSA-seq results.5.Combining BSA-seq analysis and QTL mapping results,the Z gene affecting mesocarp thickness was determined within the interval region of 57.20-57.96 Mb.Four genes homologous to those controlling rice seed development were identified in or near to this region.Gene sequence alignment revealed several SNPs and Indels occurring in the exons of the three genes,resulting in changes in amino acid sequences.Transcriptome analysis showed significant differential expression of two genes(Sobic.002G186800 and Sobic.002G192600)at different stages of seed development,and were preliminarily inferred as candidate genes for the Z locus.6.Based on sequence data,a total of 187 pairs of Indel primers were designed in the 57.20-58.11 Mb region,of which 31 pairs could amplify polymorphic fragments between the two parents.Further validation in extreme materials of RIL resulted in the identification of 4 pairs of Indel primers closely linked to mesocarp thickness,which could be used in molecular breeding of high-quality sorghum for Maotai-liquor brewing in the future. |
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