| Seed dormancy is a key domesticated trait for major crops,which is acquired in the long-term system development process and enables the survival of flowering plants to adverse natural conditions.It is a complex trait under polygenic control and affected by endogenous and environmental factors.Improving seed dormancy is an important breeding objective for the gramineae and other species.Cell wall materials are the most abundant renewable resources on the earth,which can be used for food,feed,fiber and bio-energy.As a major biomass energy crop for ethanol and feedstock,the study of cell wall related mutations in sorghum have important biological and practical significance.To identify the genomic regions controlling seed dormancy in sorghum,we used an F2 segregating population derived from a cross between a deep dormant weedy sorghum line B140 and a weak dormant grain sorghum lines CK60B.We had isolated a brittle culm mutant bcl from the ethyl methane sulphonate(EMS)-mutagenized population of sorghum variety Shangzhuang broomcom,in the present study,map-based cloning and fiunctional analysis of this mutant gene were couducted.The main results are as follows:1.Three QTLs for seed dormancy were detected in the F2 population of B14OxCK60B,two of which were located on the chromosome 4 and one was loeated on the chromosome 7 and the three QTL accounted for 15.30%?31.20%of the phenotypic variance.These QTLs were different from those reported previously.2.Using the extreme recombinants from the F3,F4 and F5 mapping populations,the major dormancy QTL,qDor7 was fine-mapped to a 96-kb genomic region on the chromosome 7,which contained 16 predicted genes in the BTx623 genome.Gene function annotation,gene expression,sequencing polymorphism and a signature of selection results showed that Sobic.007G 177000 may be the seed dormancy candidate gene in the parent B140,which need to be verified in the further study.3.Compared with wild type,the brittle culm mutant showed reduced mechanical strength in culms and leaves while other agronomic traits were indistinguishable with wild type.Cell wall morphology observation showed the wall thickness of mechanical tissue is thinner in the culm of bcl.The cellulose content reduced by 40%,the lignin content increased by 25%and glucose content decreased by approximately 40%in bcl,which indicated BC1 may involve in cell wall synthesis in culm.4.Results of genetic analysis showed that the reduced mechanical strength phenotype of bcl mutant was controlled by a single recessive gene.Using an F2 population derived from the cross between BTx623 and bcl mutant,we mapped BC1 to a 56-kb region on the chromosome 1.Comparing the genomic sequence of candidate genes in the 56-kb region in the wild type and bcl,we found a single-nucleotide change(C to A)at the position+344 from the beginning of the 2nd exon of gene,Sobic.001G336700,which results in a premature stop codon in bcl mutant,therefore,we speculated Sobic.001G336700 was the candidate gene of BC1.5.To demonstrate that Sobic.001G336700 corresponds to the bcl locus,we constructed an RNAi vector PBCI-RNAi-1 and transformed it into the switchgrass variety Alamo.Compared with wild type,the culm and leaf of all the transgenie plants showed reduced mechanieal strength.This result adequately verified that Sobic.001G336700 is the candidate gene for BC1.6.RT-PCR showed that BC1 was expressed universally throughout all organs detected with the highest expression level in stem.The relative expression level of BC1 in young and elongating stage of organs was higher than that of mature and nonelongating stage.In addition,transcriptome sequencing and RT-PCR showed that the expression level of homology in sorghum of the cell wall synthesis-related gene from rice were affected,which indicated that BC1 may regulated cellulose synthesis and cell wall assembly through affecting the expression of cell wall synthesis-related gene. |
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