Maize In Planta Haploid Inducer Lines: A Cornerstone for Doubled Haploid Technology

Lipid anchoring and electrostatic interactions target NOT-LIKE-DAD to pollen endo-plasma membrane

“…This revision of NLD localization is an essential step forward to correctly understand the biological mechanism underlying NLD function, knowing that the absence of NLD in pollen (male) causes the induction of haploid embryos with solely the maternal (female) genome in the process of in planta haploid induction ( Jacquier et al, 2020 ). In fact, the cellular insights of this study raise the challenge to explain mechanistically the astonishing fact that the loss of NLD outside the sperm cells (on endo-PM) leads to a drastic phenotype on chromosome stability within sperm cells ( Li et al, 2017 ), together with double fertilization defects ( Jacquier et al, 2020 , 2021 ). The revised NLD localization lends support to the hypothesis regarding the importance of communications between the vegetative cell and the enclosed generative or sperm cells ( McCue et al, 2011 ; Sprunck, 2020 ) during plant reproduction.…”

“…The lack of certain phospholipases impairs pollen development ( Kelliher et al, 2017 ; Gilles et al, 2017a ; Kim et al, 2011 ; Liu et al, 2017 ) and, in the case of a particular maize mutant, leads to the formation of haploid embryos with only the chromosomes from the female parent, lacking the ones from the mutant male parent ( Coe, 1959 ; Jacquier et al, 2020 ). This maize mutant, named maternal haploid inducer, represents not only an interesting resource to study pollen development and plant reproduction, but also a powerful plant breeding tool ( Gilles et al, 2017b ; Jacquier et al, 2020 , 2021 ). Maize breeders draw benefits from this reproductive anomaly, combining haploid induction with genome doubling of resulting haploid embryos/plantlets to produce doubled haploid plants.…”

“…Maize breeders draw benefits from this reproductive anomaly, combining haploid induction with genome doubling of resulting haploid embryos/plantlets to produce doubled haploid plants. Doubled haploid plants are homozygous at all loci in only two generations, compared with the traditional method taking a minimum of seven generations ( Kalinowska et al, 2019 ; Jacquier et al, 2020 , 2021 ; Widiez, 2021 ). Mutational inactivation of the gene MATRILINEAL (MTL) / NOT LIKE DAD (NLD) / ZmPHOSPHOLIPASE-A (ZmPLA1) (for simplicity, NLD hereafter) was found to cause the induction of maternal haploid embryos ( Kelliher et al, 2017 ; Gilles et al, 2017a ; Liu et al, 2017 ).…”

CRISPR-Cas technology opens a new era for the creation of novel maize germplasms

“…Doubled haploid technology can create perfectly homozygous individuals by rapidly fixing the recombinant haploid genomes on homogenous progeny, overcoming various constraints in genetic improvement and enabling rapid evaluation of phenotypic traits in maize. If a doubled haploid technology is combined with CRISPR-Cas technology, the breeders can perform faster and more precise crop breeding (Jacquier et al, 2020;Jacquier et al, 2021). In maize, the editing of ZmPOD65, ZmPLD3, ZmPLA1 and ZmDMP using CRISPR-Cas technology has successfully generated haploids, providing an approach to unravel the molecular mechanisms of haploid induction and the creation of various haploid inducers (Liu et al, 2017;Zhong et al, 2019;Jiang et al, 2022).…”

Maize Transformation: From Plant Material to the Release of Genetically Modified and Edited Varieties

“…The haploid progeny, which is typically sterile, are then screened for CRISPR–Cas-induced mutations ( Figure 4B ) and subsequently treated with a colchicine mitotic inhibitor ( Prasanna et al, 2012 ; Melchinger et al, 2016 ; Chaikam et al, 2019 ) or another less toxic doubling agent ( Geiger and Gordillo, 2009 ; Häntzschel and Weber, 2010 ) to produce fertile doubled haploid and gene-edited nontransgenic plants ( Kelliher et al, 2019 ; Wang et al, 2019 ; Figures 4C – E ). However, improvements are needed to overcome the inherent problems related to haploid induction per se ( Trentin et al, 2020 ; Jacquier et al, 2021 ). For example, CRISPR-Cas can be used before or in parallel to HI-Edit to: (1) increase the haploid induction rates by targeting genes related to high haploid induction ( Kelliher et al, 2017 ; Zhong et al, 2019 ) or genes related to the inducer exclusion ( Kelliher et al, 2019 ); (2) accelerate and accurately sort kernels/seedlings with haploid embryos from normal embryos by modifying visual traits such as anthocyanin ( Chaikam et al, 2019 ) or by integrating visible transgenic markers into the inducers ( Yu and Birchler, 2016 ; Xu et al, 2021 ; Yan et al, 2021 ) or even targeting genes involved in the oil content of seeds ( Melchinger et al, 2013 ) and fixing recessive alleles of morphological traits in donors ( Trentin et al, 2020 ).…”