Targeted mutagenesis of two homologous ATP-binding cassette subfamily G (ABCG) genes in tomato confers resistance to parasitic weed Phelipanche aegyptiaca.

Phelipanche aegyptiaca and Orobanche spp. are obligate plant root-parasitic weeds that cause extensive damage in agricultural crop plants. Their germination requires exposure to strigolactones (SLs) exuded by the host plant roots. Here we studied genes in the host plant tomato involved in SL exudation and their impact on parasitic weeds. We provide evidence that CRISPR/Cas9-mediated targeted mutagenesis of two homologous ATP-binding cassette subfamily G (ABCG) genes, ABCG44 (Solyc08g067610) and ABCG45 (Solyc08g067620), in tomato significantly reduces SLs in the root exudate and abolishes germination of the root-parasitic weed P. aegyptiaca. Based on genome sequence similarity between ABCG44 and ABCG45, a 20-bp target sequence in their exon region was selected to design single guide RNA targeting both genes using CRISPR/Cas9. The plant binary vector constructs harboring the specific Cas9 and single guide RNA were transformed into tomato. Selected T0 mutated tomato plants showed different types of deletions at both gene loci. Genotype analysis of T1 plants suggested stable inheritance of the introduced mutations without any potential off-target effects. The phenotype of Cas9-mutated plants included increased shoot branching and growth of axillary buds, and reduced length of primary stems. Interestingly, reduced germination of P. aegyptiaca resulted from a decrease in the SL orobanchol in the root exudate of Cas9-mutated plants; however, orobanchol content in the root extract was unchanged compared to control plants. Moreover, in single and double ABCG mutants, expression of the SL-biosynthesis genes CCD8 and MAX1 decreased. The current study offers insights into CRISPR-mediated mutagenesis of ABCG genes, which could serve as an efficient control method to prevent root-parasitic weed germination.