FIGURE 1.

Transgenerational gene editing and applications in plants. (A) Principle of transgenerational gene editing (TGE). A transgenic plant represented as a chromosome pair is hemizygous for a CRISPR/Cas9 containing T-DNA locus (red triangle) and edited in both alleles (stars). When crossed with a WT, the resulting progeny either lacks the T-DNA and inherits a single edited allele or inherits the T-DNA, resulting in (transgenerational) editing of the inherited WT allele. (B–D) Examples of TGE. (B) TGE for continued editing of homoeoalleles in wheat. A transgenic line may have edits only in a subset of homoeoalleles at the homologous chromosomes. After self-crossing and selecting plants that inherited the T-DNA, all homoeoalleles may now be edited (Wang et al., 2018b). (C) TGE for allelic variation. In tomato, a loss-of-function mutant (stars) also contains a CRISPR/Cas9 containing T-DNA targeting the promoter of the mutant gene. After a cross with WT, resulting T-DNA containing plants have one loss-of-function allele (star), and an allele with a promoter edit (other symbols). Every individual F1 plant has potentially a different promoter edit and phenotype as the phenotype is not determined by the inherited loss-of-function allele (Rodríguez-Leal et al., 2017). (D) Desired-target mutator (DTM) strategy. A maize plant hemizygous for a CRISPR/Cas9 containing T-DNA locus (red triangle) is crossed with an elite inbred line, resulting in TGE and editing of the elite allele. Additional rounds of TGE and backcrossing result in a new edited variety with no linkage drag (Li et al., 2017a).