Genetic transformation and regeneration in the Galena hop variety, towards CRISPR/Cas9 modification of shoot elongation

Hop has separate female and male individuals, and self-fertilization cannot be used to generate plants homozygous for recessive alleles and traits, inhibiting breeding efforts. A long-sought trait is semi-dwarfism, as hop bines require tall trellises and specialized harvesting equipment. Recently developed CRISPR/Cas9 genome editing technology can be used to generate homozygous recessive mutant alleles, potentially overcoming this issue, but typically requires initial plant transformation and regeneration of transgenic plants – technologies that are inefficient and variety-specific in hop. Here we demonstrate the first example of (1) genetic transformation and shoot regeneration in the popular hop cultivar Galena and (2) improved transformation in hop through the ectopic expression of Arabidopsis BABYBOOM and WUSCHEL transcription factors. In addition, targets for gene editing of semi-dwarfism were identified and CRISPR cassettes for loss of function genome editing were generated and introduced into the Galena variety. Transformants are currently being evaluated based on genotype and stature.