CRISPR/Cas9-Mediated Mutagenesis of Carotenoid Cleavage Dioxygenase 8 (CCD8) in Tobacco Affects Shoot and Root Architecture.

Strigolactones (SLs) are a class of phytohormones that regulate plant architecture. () genes are involved in the biosynthesis of SLs and are identified and characterized in many plants. However, the function of genes in tobacco remains poorly understood. In this study, two closely related genes and were cloned from tobacco ( L.). The two genes are orthologues of the tomato () 8 () gene. and were primarily expressed in tobacco roots, but low expression levels of these genes were detected in all plant tissues, and their transcript levels significantly increased in response to phosphate limitation. and mutations were introduced into tobacco using the CRISPR/Cas9 system and transgenic tobacco lines for both mutant alleles were identified. The and mutant alleles were inactivated by a deletion of three nucleotides and insertion of one nucleotide, respectively, both of which led to the production of premature stop codons. The mutants had increased shoot branching, reduced plant height, increased number of leaves and nodes, and reduced total plant biomass compared to wild-type plants; however, the root-to-shoot ratio was unchanged. In addition, mutant lines had shorter primary roots and more of lateral roots than wild type. These results suggest that genes are important for changes in tobacco plant architecture.