CRISPR/Cas9-mediated editing of gene in onion ( L.).

INTRODUCTION

Clustered regularly interspaced short palindromic repeats (CRISPR)/ CRISPR-associated protein 9 (Cas9) is a precise genome editing tool used to introduce genetic modifications in a wide range of crop species. Thus far, there is no report of CRISPR/Cas9-mediated genome editing in onions ().

METHODS

In the present study, we targeted two exons of the gene coding for Phytoene desaturase () in onion cv. Bhima Super. The sgRNA-carrying constructs were co-cultivated with 8-week-old embryogenic calli using an -mediated transformation protocol and incubated on the media without hygromycin B selection.

RESULTS AND DISCUSSION

Out of the total 617 co-cultivated calli, 21 (3.4%) regenerated shoots exhibited three distinct phenotypes: albino, chimeric, and pale green; in comparison to the wild-type non-transformed regenerated shoots. Total chlorophyll content was drastically reduced in albino shoots and significantly decreased in chimeric shoots. Out of the six gene PCR-confirmed regenerated shoots, two exhibited the albino phenotype due to insertions/deletions (InDels) and substitution-based mutations in and around the target sites. Deep amplicon sequencing revealed a significantly variable InDel frequency between two sgRNAs, ranging from 1.2% to 63.4%, along with a 53.4% substitution frequency. The mutation of the gene generated a visually detectable albino phenotype, thus confirming the successful editing of the gene. This is the first time a CRISPR/Cas9-mediated genome editing protocol has been successfully established in onion, with the gene serving as an example. This study will provide the necessary momentum for researchers to further basic and applied research on onions.