A rapid and highly efficient sorghum transformation strategy using GRF4-GIF1/ternary vector system

Sorghum is an important crop for food, forage, wine and biofuel production. To enhance its transformation efficiency without negative developmental by-effects, we investigated the impact of GRF4-GIF1 chimaera and GRF5 on sorghum transformation. Both GRF4-GIF1 and GRF5 effectively improved the transformation efficiency of sorghum and accelerated the transformation process of sorghum to less than 2 months which was not observed when using BBM-WUS. As agrobacterium  effectors increase the ability of T-DNA transfer into plant cells, we checked whether ternary vector system can additively enhance sorghum transformation. The combination of GRF4-GIF1 with helper plasmid pVS1-VIR2 achieved the highest transformation efficiency, reaching 38.28%, which is 7.71-fold of the original method. Compared with BBM-WUS, overexpressing GRF4-GIF1 caused no noticeable growth defects in sorghum. We further developed a sorghum CRISPR/Cas9 gene-editing tool based on this GRF4-GIF1/ternary vector system, which achieved an average gene mutation efficiency of 41.36%, and null mutants were created in the T0 generation.