Direct haploid formation in Arabidopsis using transgenic CENH3-based inducers.

Key message: This study introduces a streamlined transgenic method for generating haploid inducers using a single T-DNA construct, combining CENH3 disruption, functional complementation, and a visual marker for efficient haploid screening. The development of doubled haploid lines is crucial for plant breeding programs, but conventional inbreeding methods are laborious and costly. Centromere-mediated genome elimination using modified CENH3 histones offers an efficient single-generation approach to induce haploidy. However, this approach necessitates the generation of haploid inducer lines, which typically involves cumbersome random mutagenesis screens. In this study, we implemented a transgenic strategy to circumvent this and directly create haploid inducers in Arabidopsis. This was achieved by knocking out endogenous AtCENH3 using CRISPR/Cas while complementing it with mutated AtCENH3 variants on the same T-DNA. Four constructs with truncated or full-length AtCENH3 harboring the G83E mutation alone or with the L130F mutation, and one negative control without mutations, were transformed into Arabidopsis. Stable homozygous transgenic lines were obtained and pollinated with a glabra mutant (Atgl1). Progenies lacking RFP fluorescence and exhibiting a glabrate phenotype were recovered, and flow cytometry analyses showed their haploidy, suggesting genome elimination. Comparatively, the G83E variants showed the highest haploid induction rate. This transgenic approach directly generated haploid inducer lines in Arabidopsis while avoiding random mutagenesis. This novel transgenic strategy provides a powerful tool to rapidly establish haploid inducer lines in additional transformable crops.