Sugar accumulation enhancement in sorghum stem is associated with reduced reproductive sink strength and increased phloem unloading activity.

Sweet sorghum has emerged as a promising source of bioenergy mainly due to its high biomass and high soluble sugar yield in stems. Studies have shown that loss-of-function locus alleles have been selected during sweet sorghum domestication, and decapitation can further boost sugar accumulation in sweet sorghum, indicating that the potential for improving sugar yields is yet to be fully realized. To maximize sugar accumulation, it is essential to gain a better understanding of the mechanism underlying the massive accumulation of soluble sugars in sweet sorghum stems in addition to the locus. We performed a transcriptomic analysis upon decapitation of near-isogenic lines for mutant (, juicy stems, and green leaf midrib) and functional (, dry stems and white leaf midrib) alleles at the locus. Our analysis revealed that decapitation suppressed photosynthesis in leaves, but accelerated starch metabolic processes in stems. negatively correlates with sugar levels supported by genotypes ( vs. ), treatments (control vs. decapitation), and developmental stages post anthesis (3d vs.10d). locus gene and other programmed cell death-related genes were downregulated by decapitation, while sugar transporter-encoding gene was induced. Both and were detected in phloem companion cells by RNA assay. Loss of the homolog, in led to a sugar accumulation increase. This study provides new insights into sugar accumulation enhancement in bioenergy crops, which can be potentially achieved by reducing reproductive sink strength and enhancing phloem unloading.