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Abstract Haploid embryo seed production has been applied to accelerate plant breeding efficiency. Several genes, including DUF679 domain membrane protein (DMP) and phospholipase D3 (PLD3), are involved in maternal haploid induction in maize (Zea mays L.) and other plant species. However, how these gene variants trigger haploid induction and how they functionally interact remain largely unknown. Here, we generated CRISPR-induced DMP-knockout and examined the effects of DMP loss on the lipid composition of pollen and sperm cells in maize. Disruption of DMP led to a pronounced increase in phosphatidic acid (PA) accompanied by a decrease in phosphatidylcholine in sperm cells, with similar but weaker effects in pollen. Consistently, dmp mutants exhibited elevated transcript and protein levels of ZmPLDs, enzymes that hydrolyze phospholipids to produce PA, in both pollen and sperm cells. Immunoblot and PLD activity assays using isolated sperm cell proteins demonstrated the presence of active PLD enzymes in sperm cells and that DMP suppresses PLD activity. Manipulating sperm cell lipid composition further showed that increased PA levels, as well as the addition of DMP, enhance membrane fusogenicity. Structurally, DMP contains an N-terminal intrinsically disordered region and C-terminal transmembrane domains, and the full-length protein is required to suppress PLD activity and to promote membrane fusion. Together, these results indicate that DMP and PA have additive and compensatory effects on membrane fusion, while DMP suppresses PLD expression and PA production. These findings reveal a previously unrecognized role of DMP and its regulatory interplay with PLD in maintaining lipid homeostasis and modulating membrane fusion, providing mechanistic insights into maternal haploid induction. 

Abstract Efficient and precise targeted insertion holds great promise but remains challenging in plant genome editing. An efficient nonhomologous end-joining-mediated targeted insertion method was recently developed by combining clustered regularly interspaced short palindromic repeat (CRISPR)/Streptococcus pyogenes CRISPR-associated nuclease 9 (SpCas9) gene editing with phosphorothioate modified double-stranded oligodeoxynucleotides (dsODNs). Yet, this approach often leads to imprecise insertions with no control over the insertion direction. Here, we compared the influence of chemical protection of dsODNs on efficiency of targeted insertion. We observed that CRISPR/SpCas9 frequently induced staggered cleavages with 1-nucleotide 5′ overhangs; we also evaluated the effect of donor end structures on the direction and precision of targeted insertions. We demonstrate that chemically protected dsODNs with 1-nucleotide 5′ overhangs significantly improved the precision and direction control of target insertions in all tested CRISPR targeted sites. We applied this method to endogenous gene tagging in green foxtail (Setaria viridis) and engineering of cis-regulatory elements for disease resistance in rice (Oryza sativa). We directionally inserted 2 distinct transcription activator-like effector binding elements into the promoter region of a recessive rice bacterial blight resistance gene with up to 24.4% efficiency. The resulting rice lines harboring heritable insertions exhibited strong resistance to infection by the pathogen Xanthomonas oryzae pv. oryzae in an inducible and strain-specific manner.