| Sweet sorghum is an important energy crop,its biomass yield and stalk sugar content are the most important breeding targets. Soluble acid invertase(SAI) is a key enzyme in sugar metabolism pathway, it is impotort to understand the allelic variation and its biological effects of gene encode the enzyme to improve breeding efficiency. In this study, we cloned the full length DNA sequcence of SAI-1 gene in 80 sweet sorghum accessions and compared with 56 grain sorghum accessions. Association analysis between allelic variation and important agronomic traits were made. The relative transcriptional expression and the enzyme activity of this gene were determined at flag leaf stage and milk stage with 4 typical haplotypes of materails(35 accessions). The main results were obtained as follows:1. The full-length of SAI-1gene in 80 sweet sorghum accessions was 3953- 3967 bp, which contained 30 polymorphic loci, including 20 SNP loci, 10 InDel loci.Most allelic variations were found in non-coding introns, only 3 SNP loci were found in the coding region(the third exon). There was only one non-synonymous mutation,which was C/T mutation in the 3376 bp, led to amino acid change from A into V. 56 grain sorghum showed more polymorphic loci in SAI-1 gene sequence, which contained 45 polymorphic loci, including 15 In Del loci, 30 SNP loci, the three exons has 2, 1, 3 SNP loci, respectively. There were two non-synonymous mutations:the 1508 bp C/T mutation made amino acid changed from T to I and the 3376 bp T/C mutation made amino acid changed from A into V. Tajima’D test showed that the SAI-1 gene of both sweet sorghum and grain sorghum conform to the neutrality test. The degree of linkage disequilibrium among polymorphic sites was stronger in sweet sorghum than in grain sorghum.2. Association analysis showed that SAI-1 allelic variation was signicantly associated with main agronomic traits such as plant height, stem diameter, fresh weight per plant, dry weight per plant and sugar content(Brix). Sequence length of the first intron was significantly positively related with yield related traits, weakly negatively related with sugar content. It was on the contrary for the second intron, and signicantly positively correlation between the length and sugar content. Total sequence of both introns showed the same trend as the second intron in these correlations, which proved the second intron took key roles in regulating the yield formation. Of the 30 polymorphic sites in 80 sweet sorghum accessions, 12 sites were significantly associated with all agronomc traits test. Variation at the 985 bp site in the first and the 2964 bp site in the second intron contributed mostly to the association.3. Four sweet sorghum haplotypes showed significantly difference in relative expression and enzyme activity of the SAI-1 gene in stem at flag leaf stage and milk stage. At flag leaf stage, SAI-1a2 haplotype had the highest SAI-1 gene relative expression level, and then is SAI-1a1, SAI-1b and SAI-1c in descending order. At the milk stage, SAI-1a1 showed the highest relative expression, then SAI-1a2, SAI-1b and SAI-1c. For the enzyme activity, four haplotypes showed the effect trend at both stage, SAI-1a1, SAI-1a2, SAI-1b, SAI-1c decreased in the order.The result described above showed that SAI-1 is significantly associatd with yield traits and sugar content, and the repeat number of 5 bases “ATTGA” in the second intron palyde an important role in regulating yield formation and sugar accumulation. The function marker developed in our laborory which called SBX1 for sugar content will be useful in sweet sorghum breeding for high yiled. |
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