The DELLA protein is responsible for repressing growth in plants leading to a dwarf trait. A fully functional DELLA protein is sensitive to gibberellic acid (GA), which promotes DELLA degradation and thus plant growth. Several loss-of-function mutations in the DELLA-encoding gene PROCERA are present in cultivated crops like tomato, barley, and rice. 

Researcher Laurence Tomlinson and colleagues from Norwich Research Park in UK and University of Minnesota in the USA used CRISPR-Cas9 to edit the gene coding for DELLA proteins in tomato. Tomatoes are economically important and widely studied for traits such as disease resistance, fruit shape, and color. Aiming for a tomato with a dwarf trait will reduce the need for additional mechanical support, pruning, and side support management.

Results of the study showed the generation of three transgene-free heritable genotypes through genome editing. The first genotype is homozygous PRO^D/PRO^D, which confer the dwarf trait and partial responsiveness to GA; the second one is heterozygous PRO^D/PRO, which had intermediate height when young but dwarf when matured. The mutation introduced is therefore dominant. The third genotype is also a loss-of-function mutation that conferred traits like the DELLA-silenced plant. 

For more information, read the article in Plant Biotechnology Journal.