Sweet Sorghum Originated through Selection of <i>Dry</i>, a Plant-Specific NAC Transcription Factor Gene

Abstract

Sorghum (<i>Sorghum bicolor</i>) is the fifth most popular crop worldwide and a C₄ model plant. Domesticated sorghum comes in many forms, including sweet cultivars with juicy stems and grain sorghum with dry, pithy stems at maturity. The <i>Dry</i> locus, which controls the pithy/juicy stem trait, was discovered over a century ago. Here, we found that <i>Dry</i> gene encodes a plant-specific NAC transcription factor. <i>Dry</i> was either deleted or acquired loss-of-function mutations in sweet sorghum, resulting in cell collapse and altered secondary cell wall composition in the stem. Twenty-three <i>Dry</i> ancestral haplotypes, all with dry, pithy stems, were found among wild sorghum and wild sorghum relatives. Two of the haplotypes were detected in domesticated landraces, with four additional <i>dry</i> haplotypes with juicy stems detected in improved lines. These results imply that selection for <i>Dry</i> gene mutations was a major step leading to the origin of sweet sorghum. The <i>Dry</i> gene is conserved in major cereals; fine-tuning its regulatory network could provide a molecular tool to control crop stem texture.