Sorghum in scope: high protein, gene editing and nitrogen dynamics

Abstract

Drought and heat tolerance is increasingly becoming a valuable trait sought worldwide to address food security and climate change. This trait is one of the most valued in sorghum, however, its usefulness as a food and feed crop are limited due to its low protein content, a poor starch/protein digestibility, and small grain size. These downsides are the reason why sorghum is considered as a minor crop. Additionally, the recalcitrant nature of sorghum in tissue culture supposes an added challenge for new breeding technologies.
To add value to the crop, we aim to develop a high-protein gene edited sorghum. Previous studies by our group successfully silenced FOLDASE using miRNA in sorghum, leading to a higher overall protein content and greater grain digestibility phenotype without any clear pleiotropic effects upon yield (Unpublished data). FOLDASES are folding catalyst and chaperones involved in maintaining the homeostasis, plant development, response to biotic and abiotic stresses.

Two strategies are being followed to develop a partial loss of function mutant. At the genetic level, a knock-down of FOLDASE by making a deletion in the promoter region is being generated to reduce gene expression. In parallel, at the protein level, a mutant protein FOLDASE with a reduced catalytic activity has been designed. In silico analyses have identified amino acid substitutions that potentially reduce FOLDASE activity. Additionally, an expression system for FOLDASE has been developed to analyse how these mutations impact protein structure and enzymatic function in vitro. Edited lines from both strategies are being generated to test their physiological behaviour, particularly regarding nitrogen use dynamics. One of the main questions is whether they need a higher uptake of nitrogen from soil or remobilise nitrogen more efficiently.

Finally, all gene edited lines share the same genetic background so the results must be demonstrated in elite commercial hybrid parents to understand the broad applicability of this approach. Further validation of grain quality and phenotype of these edited lines could unlock the potential of this drought tolerant crop, addressing one of sorghum's principal limitations.