Spotlight on plant double fertilisation

With EU funding, the GAMETEFUSION project has uncovered signalling mechanisms in double fertilisation. The importance of this process cannot be understated as one fertilisation gives rise to the embryo and the other a nutrient-rich food source for the developing plant.

Studying the model plant Arabidopsis thaliana, the researchers looked at two sperm-enriched tetraspanins (TETs), also signalling mediators in diverse processes in animal systems: adhesion and gamete fusion. Gene expression analysis confirmed that TETs are membrane-associated proteins in specific reproductive tissues including gametes.

Similar to their animal counterparts, TETs' functions in plants may depend on the assembly of multi-molecular membrane complexes that rely on presence of potential binding partners. The unique localisation pattern found for the TETs in the interface of both types of sperm cell suggests a membrane scaffold could be involved in mediating sperm-sperm cell adhesion or communication.

The GAMETEFUSION team identified two potential TET binding partners. Using knockout mutants, fertility defects occurred, such as a single fertilisation. This finding is relevant in particular as a heightened understanding of cellular processes behind gamete differentiation and double fertilisation may contribute to possible divergent and conserved mechanisms in plants and animals.

Researchers developed a fluorescence-activated cell sorting tool to isolate individual subcellular components of the male gametophyte and analysed their repertoires of expressed messenger RNAs (mRNAs). Researchers plan to detect and track sperm mRNAs during male gamete differentiation and pollen tube growth. The experimental system represents the first application of an in vivo system to image mRNA movement in pollen. Scientists expect to reveal molecular events during double fertilisation and early embryogenesis.

GAMETEFUSION has developed several unparalleled molecular tools that are already or will become available to the scientific research community. Ability to manipulate the fertilisation process has powerful applications in the field of plant breeding.