EMBO: A common strategy to create high-yielding plants is hybrid breeding –
crossing two different inbred lines to obtain characteristics superior
to each parent. However, getting the inbred lines in the first place can
be a hassle. Inbred lines consist of genetically uniform individuals
and are created through numerous generations of self-crossing. In maize,
the use of so-called “haploid inducers” provides a short cut to this
cumbersome procedure, allowing to produce inbred lines in just one
generation. A study by Laurine Gilles and colleagues, published today in
The EMBO Journal, sheds light on the genetics behind haploid
induction. “Knowing the molecular identity of haploid induction
represents an important breakthrough to fully understand the
fertilization process in plants, and hopefully will allow to translate
this breeding tool to other species,” said the study’s senior author Dr.
Thomas Widiez, an INRA (Institut National de la Recherche Agronomique)
researcher at the École Normale Supérieure in Lyon, France.
Haploid inducers were first discovered in the 1950s. Pollination of
female flower with pollen of a haploid inducer strain will yield
offspring that are haploid, meaning that they will only contain one
single copy of each gene as opposed to the usual two copies. All their
genetic material comes from the mother. Treating these haploid plants
with a chemical that causes chromosome doubling will lead to plants with
two identical copies of all genes in just one generation. With
classical inbreeding, this condition takes seven to ten years to
achieve.
Haploid offspring in maize are not unusual; they emerge naturally,
albeit at a very low rate. Haploid inducers can bring this rate up to
about 10% of the progeny being haploid - enough to make it a useful tool
for breeders. More than 50 years after the discovery of haploid
inducers, Widiez and his team, in collaboration with Limagrain, have now
identified the gene that mainly causes the phenomenon and termed it Not Like Dad
to highlight the fact that its dysfunction induces embryos without
genetic contribution from the father. The gene product is necessary for
successful fertilization so that its failure promotes the formation of
haploid embryos. Two other research groups have in parallel identified
the same gene and come to similar conclusions.
Haploid inducers are nowadays powerful breeding tools, but as yet the
technology is restricted to maize, while in-vitro haploid induction in
certain crops is labor-intense. Understanding the genes and molecular
mechanism behind the process will help translate this technology to
other crops. The identification of Not Like Dad is an important step to this end. While Not Like Dad
is the most important contributor to haploid induction in inducer
lines, there are at least seven more genes that play a role in
increasing the rate of haploid offspring. Revealing their molecular
identity, as well as understanding their mode of action, will be
important to fully understand the process.
Loss of pollen-specific phospholipase Not Like Dad (NLD) triggers gynogenesis in maize
Laurine M Gilles, Abdelsabour Khaled, Jean-Baptiste Laffaire,
Sandrine Chaignon, Ghislaine Gendrot, Jérôme Laplaige, Hélène Bergès,
Genséric Beydon, Vincent Bayle, Pierre Barret, Jordi Comadran,
Jean-Pierre Martinant, Peter M. Rogowsky and Thomas Widiez
Read the paper: doi: 10.15252/embj.201796603