Pollen self-elimination CRISPR–Cas genome editing prevents transgenic pollen dispersal in maize

Genome editing with clustered regularly interspaced short palindromic repeats (CRISPR)–CRISPR-associated nuclease (Cas)-mediated technologies have revolutionized basic plant science and crop genetic improvement (Chen et al., 2019). Stable genetic transformation of CRISPR–Cas cassette(s) is the main approach to genome editing in planta. In many sexually reproducing plants, a major concern is the dispersal of genetically modified elements through pollen (Devos et al., 2005). Maize (Zea mays L.), a typical outcrossing crop species, can produce as many as two to five million pollen grains per plant (Goss, 1968) and has a recommended isolation distance of 200 m due to wind dispersal (Ma et al., 2004) or even >3 km due to foraging by insects like honey bees (Danner et al., 2014). A previously reported strategy using suicide transgenes effectively killed immature embryos and pollen harboring a Cas9 transgene produced by T0 plants and produced transgene-free edited T1 plants (Heet al., 2018). Especially for vegetativy propagated plants, this technology solves the problem of removing transgenic components, as it is not feasible to remove them through meiotic recombination and segregation. However, genome editing has a number of useful applications for which the Cas transgene needs to be retained in the plants, including RNA guided Cas9 as an in vivo desired-target mutator (Li et al., 2017) and haploid induction-coupled editing (Kelliher et al., 2019; Wang et al., 2019) through the paternal haploid using acenh3-null mutant as the female gametophyte (Ravi and Chan, 2010). In this correspondence, we present PSEC, which prevents pollen transgene dispersal from plants that harbor a T-DNA containing a pollen suicide cassette next to specific single guide RNA and Cas cassettes. At the same time, PSEC can still be inherited through the female gamete to the next generation and also retains CRISPR–Cas gene editing activity. Through sexual crossing, it acts in trans to induce efficient target mutations in the parental genome of crosses for breeding applications.