Genetic transformation and genome editing of flax (Linum usitatissimum L.): current status and future perspectives

Flax (Linum usitatissimum L.) is an important multipurpose crop cultivated for fiber, oil (edible and industrial), and bioactive compounds used in medicine and cosmetics, making reliable transformation methods essential for targeted product quality improvement. This review compares three classic delivery platforms (Agrobacterium-mediated transformation, protoplast transformation, and particle bombardment) regarding efficiency, chimerism frequency, reproducibility, and suitability for genome editing, while also discussing virus-mediated delivery as a developing alternative. Currently, Agrobacterium-mediated transformation of hypocotyls followed by callus induction is widely used, but untransformed escapes and chimerism complicate the production of fully transgenic plants. This issue is mitigated when anther-derived calli are used as explants instead of hypocotyls and is absent in floral dip and protoplast transformation methods. Promising genome editing approaches now target the generation of non-transgenic flax plants. Although transgene-free lines were reportedly obtained through Cas-mediated oligonucleotide-directed mutagenesis (a single-stranded oligonucleotide template combined with transient clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein (Cas) and transcription activator-like effector nucleases (TALEN) expression) in protoplasts, the lack of data confirming the absence of transgenes undermines these findings, therefore, verification of the obtained plants is essential. In theory, ribonucleoprotein (RNP) complexes could achieve a sufficient editing outcome via particle bombardment or delivery to protoplasts. Similarly, virus-induced genome editing (VIGE) utilizing viral vectors to deliver CRISPR/Cas components is also suggested as a viable approach to generate non-transgenic genome-edited plants, which is particularly advantageous as it bypasses the highly challenging plant regeneration stage.