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RNA from maternal plant tissue ensures seed development
How does a single plant cell become a functional pollen? And who tells the pollen what to do? A new study shows that pollen development is influenced by more than just its own blueprint. Instead, they receive crucial molecular “text messages” from maternal plant tissue. These can be transported over long distances within the plant. Researchers at the Max Planck Institute of Molecular Plant Physiology (MPI-MP) report these findings in a recent publication in Nature Plants.
Small RNAs are short RNA molecules that help determine which genes in a cell are switched on or off. Until now, it was assumed that the small RNAs necessary for pollen development originate in the pollen itself and in the directly surrounding maternal tissue. However, the new study conducted by the MPI-MP reveals a surprisingly different picture: the crucial signals do not originate in the pollen, but in maternal tissue and can be transported over long distances, for example from the roots.
To find out where these signals come from, the research team led by Prof. Dr. Claudia Köhler used the method of grafting, a classic yet effective technique in which the shoot of one plant is joined to the rootstock of another. A species related to shepherd's purse served as a model (Capsella rubella).
Unexpected senders: instructions for pollen from maternal tissue
The researchers specifically switched off RNA polymerase IV (Pol IV) in the shoots of Capsella. This is an enzyme that is necessary for the production of certain small RNAs. If Pol IV is missing, pollen development in plants of the genus Capsella stops early: Hardly any mature pollen is produced and the plants fail to produce seeds.
But then, surprisingly, when a modified shoot was grafted onto an unmodified rootstock, the plants formed mature pollen and produced seeds. This shows that a mobile signal, in this case from the root, can control pollen development in the shoot. The plant thus organizes its reproduction over long distances with the help of molecular “text messages.”
“Our data shows that small RNAs can act as mobile instructions for development,” explains first author Jiali Zhu. “They are formed in maternal tissues, enter the male part of the plant, and are crucial for normal pollen maturation there.”
No epigenetic repair, but targeted interventions
Pol IV is normally part of a well-known epigenetic mechanism called RNA-directed DNA methylation. This process permanently silences genes or mobile DNA elements. However, this mechanism alone did not explain the new observations.
Although small RNAs reappeared in the pollen after grafting, they did not restore the missing DNA methylation. Instead, the data suggests that the mobile RNAs act after the genes have been transcribed and specifically break down certain RNA molecules. The “text messages” from the maternal tissue thus directly intervene in ongoing processes instead of leaving longer-term epigenetic traces.
A hidden system is revealed
Particularly surprising is the similarity of these small RNAs to so-called reproductive phasiRNAs. These are known from many flowering plants, where they play a central role in male fertility. In the Brassicaceae plant family, which includes cabbage and mustard in addition to Capsella rubella, such systems were long thought to be absent.
The new study now suggests that there is indeed a phasiRNA-like mechanism in Capsella, but that it is triggered differently: not by classic miRNA triggers (these are special small RNAs), but by mobile, Pol IV-dependent small RNAs.
Why this changes our view of plants
“It is very likely that this mechanism is also conserved in other plant species,” says Prof. Claudia Köhler, director at the Max Planck Institute of Molecular Plant Physiology and co-author of the study. “This finding opens up a number of exciting follow-up questions: What ‘messages’ are generated in maternal tissues? How are they transported through the plant? And to what extent does the plant in this way link its reproduction to environmental conditions or its own developmental state? Plant reproduction is a very finely tuned process in which there are still several hidden variables to be discovered.”
The study changes our understanding of plant reproduction, showing that small RNAs can act as mobile messengers over long distances, thereby specifically controlling the development of the next generation.
Prof. Dr. Claudia Köhler
Director
Max Planck Institute of Molecular Plant Physiology
Mail: Koehler@mpimp-golm.mpg.de
Tel.: +49 331 567-8100
Zhu, J., Santos-González, J., Wang, Z. et al. Long-distance transport of siRNAs with functional roles in pollen development. Nat. Plants (2026). https://doi.org/10.1038/s41477-026-02219-6
https://www.nature.com/articles/s41477-026-02219-6
Dr. Jiali Zhu studied grafted plants of the species Capsella rubella for her work.
Quelle: MPI-MP/sevens+maltry
Copyright: MPI-MP/sevens+maltry
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