CRISPR/Cas9-Mediated Editing of AGAMOUS-like Genes Results in a Late-Bolting Phenotype in Chinese Cabbage (Brassica rapa ssp. pekinensis)

Abstract

Due to the sudden change in temperature in spring, Chinese cabbage, a leafy vegetable cultivated for consumption, loses its commercial value due to the onset of bolting—the phenomenon of switching from vegetative to reproductive growth. In this study, we applied clustered regularly interspaced short palindromic repeats/(CRISPR)-associated system 9 (CRISPR/Cas9) technology to analyze AGAMOUS-like genes. We performed functional analysis of AGL19 and AGL24 genes related to bolting and flowering using CRISPR/Cas9-mediated Chinese cabbage transformation. Single-guide RNA (sgRNA) sequences were created with a low off-targeting probability to construct gene-editing vectors. Agrobacterium-mediated transformation was conducted, and tentative E0 AGL-edited lines were analyzed using molecular biotechnological methods. Two AGL19-edited lines with nucleotide sequence mutations in the target sequence of the AGL19 genes and four AGL24-edited lines with nucleotide sequence mutations in the target sequence of the AGL24 genes showed particularly late bolting compared to the inbred line ‘CT001.’ Generational progression using bud pollination obtained T-DNA-free E1 AGL-edited lines, which also showed late bolting. The loss of function of the AGL protein was caused by the occurrence of an indel mutation in the AGL19 and AGL24 genes, which results in an early stop codon. Furthermore, frameshift mutations led to structural changes and the introduction of an early stop codon in the AGL19 and AGL24 proteins. Our results indicate that CRISPR/Cas9-mediated editing of AGAMOUS-like genes results in a late-bolting phenotype and that CRISPR/Cas9 is a useful technology for analyzing gene function in Chinese cabbage (Brassica rapa ssp. pekinensis).