title: MATRILINEAL, a sperm-specific phospholipase, triggers maize haploid induction.
abstract: Sexual reproduction in flowering plants involves double fertilization, the union of two sperm from pollen with two sex cells in the female embryo sac. Modern plant breeders increasingly seek to circumvent this process to produce doubled haploid individuals, which derive from the chromosome-doubled cells of the haploid gametophyte. Doubled haploid production fixes recombinant haploid genomes in inbred lines, shaving years off the breeding process. Costly, genotype-dependent tissue culture methods are used in many crops, while seed-based in vivo doubled haploid systems are rare in nature and difficult to manage in breeding programmes. The multi-billion-dollar maize hybrid seed business, however, is supported by industrial doubled haploid pipelines using intraspecific crosses to in vivo haploid inducer males derived from Stock 6, first reported in 1959 (ref. 5), followed by colchicine treatment. Despite decades of use, the mode of action remains controversial. Here we establish, through fine mapping, genome sequencing, genetic complementation, and gene editing, that haploid induction in maize (Zea mays) is triggered by a frame-shift mutation in MATRILINEAL (MTL), a pollen-specific phospholipase, and that novel edits in MTL lead to a 6.7% haploid induction rate (the percentage of haploid progeny versus total progeny). Wild-type MTL protein localizes exclusively to sperm cytoplasm, and pollen RNA-sequence profiling identifies a suite of pollen-specific genes overexpressed during haploid induction, some of which may mediate the formation of haploid seed. These findings highlight the importance of male gamete cytoplasmic components to reproductive success and male genome transmittance. Given the conservation of MTL in the cereals, this discovery may enable development of in vivo haploid induction systems to accelerate breeding in crop plants.
authors.affiliation: Seeds Research, Syngenta Crop Protection, 9 Davis Drive, Research Triangle Park, North Carolina 27709, USA.
authors.forename: Timothy
authors.initials: T
authors.lastname: Kelliher
authors.affiliation: Seeds Research, Syngenta Crop Protection, 9 Davis Drive, Research Triangle Park, North Carolina 27709, USA.
authors.forename: Dakota
authors.initials: D
authors.lastname: Starr
authors.affiliation: Seeds Research, Syngenta Crop Protection, 9 Davis Drive, Research Triangle Park, North Carolina 27709, USA.
authors.forename: Lee
authors.initials: L
authors.lastname: Richbourg
authors.affiliation: Syngenta Seeds, 2369 330th Street, Slater, Iowa 50244, USA.
authors.forename: Satya
authors.initials: S
authors.lastname: Chintamanani
authors.affiliation: Syngenta Seeds, 4133 East County Road O, Janesville, Wisconsin 53546, USA.
authors.forename: Brent
authors.initials: B
authors.lastname: Delzer
authors.affiliation: Seeds Research, Syngenta Crop Protection, 9 Davis Drive, Research Triangle Park, North Carolina 27709, USA.
authors.forename: Michael L
authors.initials: ML
authors.lastname: Nuccio
authors.affiliation: Seeds Research, Syngenta Crop Protection, 9 Davis Drive, Research Triangle Park, North Carolina 27709, USA.
authors.forename: Julie
authors.initials: J
authors.lastname: Green
authors.affiliation: Seeds Research, Syngenta Crop Protection, 9 Davis Drive, Research Triangle Park, North Carolina 27709, USA.
authors.forename: Zhongying
authors.initials: Z
authors.lastname: Chen
authors.affiliation: Seeds Research, Syngenta Crop Protection, 9 Davis Drive, Research Triangle Park, North Carolina 27709, USA.
authors.forename: Jamie
authors.initials: J
authors.lastname: McCuiston
authors.affiliation: Seeds Research, Syngenta Crop Protection, 9 Davis Drive, Research Triangle Park, North Carolina 27709, USA.
authors.forename: Wenling
authors.initials: W
authors.lastname: Wang
authors.affiliation: Seeds Research, Syngenta Crop Protection, 9 Davis Drive, Research Triangle Park, North Carolina 27709, USA.
authors.forename: Tara
authors.initials: T
authors.lastname: Liebler
authors.affiliation: Syngenta Seeds, 2369 330th Street, Slater, Iowa 50244, USA.
authors.forename: Paul
authors.initials: P
authors.lastname: Bullock
authors.affiliation: Seeds Research, Syngenta Crop Protection, 9 Davis Drive, Research Triangle Park, North Carolina 27709, USA.
authors.forename: Barry
authors.initials: B
authors.lastname: Martin
mesh_terms: D000483:Alleles; D001947:Breeding / Q000379:methods; D003593:Cytoplasm / Q000201:enzymology; D005306:Fertilization; D016368:Frameshift Mutation; D000072669:Gene Editing; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant / Q000235:genetics; D005816:Genetic Complementation Test; D006238:Haploidy; D010641:Phenotype; D010740:Phospholipases / Q000235:genetics* / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism; D011058:Pollen / Q000166:cytology / Q000201:enzymology* / Q000235:genetics; D012639:Seeds / Q000235:genetics; D017423:Sequence Analysis, RNA; D003313:Zea mays / Q000166:cytology / Q000201:enzymology* / Q000235:genetics*
chemical_list: D010940:Plant Proteins; D010740:Phospholipases