Progress and challenges in sorghum biotechnology, a multipurpose feedstock for the bioeconomy

Abstract

Sorghum [Sorghum bicolor (L.) Moench] is the fifth most important cereal crop globally by harvested area and production. Its drought and heat tolerance allow high yields with minimal input. It is a promising biomass crop for the production of biofuels and bioproducts. In addition, as an annual diploid with a relatively small genome compared with other C4 grasses, and excellent germplasm diversity, sorghum is an excellent research species for other C4 crops such as maize. As a result, an increasing number of researchers are looking to test the transferability of findings from other organisms such as Arabidopsis thaliana and Brachypodium distachyon to sorghum, as well as to engineer new biomass sorghum varieties. Here, we provide an overview of sorghum as a multipurpose feedstock crop which can support the growing bioeconomy, and as a monocot research model system. We review what makes sorghum such a successful crop and identify some key traits for future improvement. We assess recent progress in sorghum transformation and highlight how transformation limitations still restrict its widespread adoption. Finally, we summarize available sorghum genetic, genomic, and bioinformatics resources. This review is intended for researchers new to sorghum research, as well as those wishing to include non-food and forage applications in their research.

Keywords: Agrobacterium; biofuels; bioinformatic resources; genetic engineering; genetic resources; sorghum transformation.

Fig. 1.

Sorghum plant morphology (A) and panicle and spikelet phenotypes of the five basic races (B). The race bicolor is the most primitive of the cultivated races and has upright semi-open panicles, with long and clasping glumes. Commercially cultivated sorghum tends to be a mixture of these major races. The race guinea originated in humid regions of West Africa and has open, elongated panicles, which helps decrease mold infection. Caudatum originated in eastern Africa and has panicles ranging from compact to open, with shorter, asymmetric, glumes that expose the grain. On the other hand, kafir, which originated in southern Africa, has tighter and longer panicles. Durras have compact panicles and originated in southern Sahara.

Fig. 2.

Timeline of advances in sorghum transformation. Cat, chloramphenicol acetyltransferase; NptII, neomycin phosphotransferase II.

Fig. 3.

Representation of transformation methods adopted for sorghum. GOI, gene of interest; CIM, callus induction media.