Sweet sorghum was originally cultivated in the U.S. for the production of food-grade syrup or alcohol, and it still has commercial value as a source of these commodities, as well as an important bioenergy crop.  Understanding the genetic mechanisms underlying sugar production and storage in sorghum is of great interest to both biologists and breeders, and the genes in this pathway represent potential targets for crop improvement.


To enable investigation of genomic differences between sweet and grain-type sorghums, researchers at the University of North Carolina at Charlotte and Clemson University in South Carolina, with support from the Community Sequencing Program (CSP) at the DOE’s Joint Genome Institute (JGI), have generated a high-quality reference genome for sweet sorghum based on the archetypal ‘Rio’ genotype (Cooper et al. 2019).  By comparing this new genome with the original sorghum reference, which comes from the short-stature, early maturing ‘BTx623’ genotype used for the production of grain sorghum hybrids, the authors identified 54 genes that were present only in Rio, along with 276 genes present only in BTx623.  Of the genes that were deleted in Rio, three are known sucrose pathway genes from the SWEET transporter family, suggesting that changes in sugar transport, rather than sugar synthesis, may be key to the sweet phenotype in sorghum.  Consistent with that idea, complementary transcriptomics analysis also uncovered differential expression and post-transcriptional regulation of many genes involved in sugar transport.


In addition to finding differences directly related to sugar accumulation, comparison of the Rio and BTx623 reference genomes revealed more than 2 million mutations, more than 100,000 of which are in the coding regions of genes.  The discovery of these mutations, along with the identification of more than 300 gene presence/absence variants, confirms that the Rio genome will provide a useful resource for future agronomic and physiological studies, allowing sorghum researchers to better identify changes in genomic architecture that may be linked to important phenotypes.


The latest version of the Rio genome and its annotation can be found on Phytozome (https://phytozome.jgi.doe.gov/pz/portal.html).  To download data or browse the genome, go to the ‘Species’ tab on the Phytozome home page and select ‘Sorghum bicolor Rio v2.1’.  Or, to directly link to the genome, use: https://phytozome-next.jgi.doe.gov/info/SbicolorRio_v2_1.


Raw data and data from the transcriptomics study are available for download from the NCBI SRA database under BioProject PRJNA331825.

A New Reference Genome for Sweet Sorghum
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