Genetic Basis of Stem Growth in Sorghum

Sorghum is the fifth most widely grown crop worldwide, by acreage.  While grown primarily for grain in the U.S., it is also grown for forage, sugar, and, increasingly, biofuels.  In its native Africa, sorghum accessions are often 3-4 meters tall; however, U.S. grain sorghum was bred for reduced height to decrease lodging and to aid machine harvesting.  For biofuel production, increasing height can increase stem sugar and/or biomass yield.  In order to further our knowledge of this important trait, we examined the diversity of the sorghum germplasm from the Sorghum Association Panel with Digital Genotyping at ~50,000 loci.  In the 1950s, it was determined that there are four major loci that control height in sorghum, named Dw1-Dw4.  Dw3 was previously identified as the IAA transporter ABCB1, an ortholog of Br2 in maize (Multani et al., 2003).  In the present study, QTL mapping in biparental populations was used to locate loci that control height, including Dw1 and Dw2.  Furthermore, a set of accessions with different Dw1-Dw4 alleles was used to examine gene expression variation in growing internodes.  RNA-seq revealed differentially expressed genes during stem internode development and between the diverse germplasm providing new information about the genetic basis of height in sorghum.