Chloroplast Genome Characteristics and Phylogenetic Relationships of Different Sorghum Germplasms

Sorghum (Sorghum bicolor) is the fifth largest cereal crop in the world and is an important food and feed crop. However, the understanding of the chloroplast genome of sorghum is limited, especially for some landrace varieties. In this study, the complete chloroplast (cp) genomes of 10 sorghum varieties from southwestern China were assembled and analysed in depth. The genome sizes ranged between 140.644 and 140.814 bp; the b3 variety had the smallest genome size, and the b6, b7 and b8 varieties had the largest. Highly conserved sequences were found among the 10 cp genomes. A total of 136 genes, including 88 protein-coding genes, 40 tRNAs and 8 rRNAs, were found in each cp genome. Comparative genomic analysis revealed that the large single-copy (LSC) region had more SNPs and indels than the inverted repeat (IR) and small single-copy (SSC) regions. Furthermore, some genes, including matK, matK-trnk, psbM-petN, rps12-rpl20, and ccsA, exhibited greater sequence variation than others. Furthermore, phylogenetic analysis revealed that b3 had a distant genetic relationship with the other 9 varieties. Our findings provide valuable information for a deeper understanding of the genetic structure of sorghum germplasm resources globally and provide an important foundation for subsequent genetic improvement of sorghum.