24 May 2022, Ghent, Belgium
To produce fruits and seeds, plants need to be fertilized in a narrow time frame during which the flower is receptive to viable pollen. In crops, excessive heat and drought stress can negatively impact fertilization causing a reduction in seed yield. Collaborative research between the VIB-UGent Center for Plant Systems Biology and Corteva AgriscienceTM identified a key regulatory mechanism to prolong female fertility in maize. This knowledge may become an important asset to stabilizing seed production for maize, and potentially for other cereal crops growing in changing climate conditions caused by global warming.
Let’s talk about maize
Maize is a high-yielding cereal crop and therefore staple food throughout most of the world. To obtain high grain yields, an ear with full seed set requires optimal fertilization conditions in which the receptiveness of the female inflorescence (flower) is synchronized with the presence of viable pollen. Environmental stresses such as heat and drought reduce the time frame in which viable pollen availability and female fertility including silk viability overlap, causing reduced seed yield.
“In light of climate change, knowledge on the modulation of female fertility can become increasingly important in our struggle to stabilize seed yield under adverse environmental conditions,” according to prof. Moritz Nowack (VIB-UGent).
More particularly, the duration of female flower fertility of maize is a critical characteristic in grain yield and thus important for farmers. Extending the time window during which the female flower of maize can be pollinated by delaying the process of floral aging can increase the chance of a complete seed set on maize ears in suboptimal growing conditions.
Don’t KIL(1) me now
Female maize flowers develop elongated silk structures. Once airborne pollen from maize tassels lands on silks, the pollen tubes grow through the silk strand toward the ovary where fertilization occurs. When floral aging sets in, the receptivity period of the silk ends, and the potential of seed production is irreversibly lost. The Nowack lab, which studies programmed cell death in a developmental context, in collaboration with maize scientists from Corteva Agriscience, a global agriculture company, identified molecular factors that determine the longevity of silk viability.
Together, researchers from both organizations discovered that KIRA-LIKE1 (KIL1) is the main gene regulating the loss of female fertility induced by the aging of the maize silks. Maize plants in which KIL1 gene function is lost – indicated as kil1 – show delayed flower aging leading to a prolonged period of female flower receptivity to pollen. The researchers found that when KIL1 is expressed it initiates cell death at the base of each silk strand, causing the strand to collapse and preventing the pollen tube from reaching and fertilizing the female flower ovary. The result is that KIL1 terminates the receptivity period of the silk.
Tom Greene, Senior Research Director and Leader of Biotechnology at Corteva says, “For decades we have known that silk receptivity is a critical component to determining grain yield in maize. Now that we also know one of the key genes that control this natural function, we can target this gene to further enhance maize productivity for our customers, helping to drive higher yields.”
Cell death determines new life
Programmed cell death is inherently part of life. It is tightly controlled and shapes developmental processes that contribute to plant growth and reproduction. The results from this study indicate a role for programmed cell death in regulating plant fertility, in several plant species. KIRA1, the KIL1 counterpart in Arabidopsis, has a similar function in terminating flower fertility using programmed cell death. Despite a large evolutionary distance between maize and Arabidopsis, the mechanism of fertility control appears to be conserved.
“Fertility mechanisms that are common among plants are intriguing targets for plant improvement. With this new discovery we have an opportunity to enhance fertility not only in maize, but also in other crop plants to improve their seed yield,” indicates Jeff Habben, Senior Research Manager at Corteva. “This discovery and our collaboration with the VIB-UGent Center for Plant Systems Biology has the potential to help us address one of the many pressures farmers face: the ability to do more with less in more precise and planet-friendly ways.”
Šimášková et. al., The Plant Cell 2022