High-throughput haploid induction in species with bisexual flowers

Dear Editor,Doubled haploid(DH)technology can significantly accelerate the development of homozygous lines.DH breeding has achieved great success inmaize because of the discovery of the first haploid inducer,Stock6,and the development of a series of high-efficiency haploid inducers(Hu et al.,2016).Pioneering studies on the genetic basis of haploid induction(HI)revealed that loss-offunction mutation of the phospholipase gene ZmPLA1/MATL/NLD triggers HI and that the HI rate(HIR)can be dramatically enhanced by a single nucleotide substitution from T to C in ZmDMP(Jacquier et al.,2020).Remarkably,knockout of ZmPLA1/MATL/NLD homologs in rice,wheat,and foxtail millet results in HIRs of 2%–6%,5%–15%,and 2%–3%,respectively(Jacquier et al.,2020;Cheng et al.,2021).In addition,loss of function of ZmDMP-like genes enables HI in species including Arabidopsis,tomato,rapeseed,tobacco,etc.,with an average HIR of around 2%(Zhong et al.,2020,2022a,2022b).These successes have laid solid foundations for the construction of a universal DH breeding system in different crop species.More importantly,HI-Edit/IMGE systems that enable gene editing in elite germplasms have been established on the basis of HI,making HI even more important(Kelliher et al.,2019;Wang et al.,2019).