One RNA-Binding Protein Rewrites How Young Plants Grow Up

Every plant has an awkward adolescence. In the weeks after germination, a seedling lives out a juvenile phase — small, soft leaves, rapid growth, no thought of reproduction — before quietly shifting into adulthood, when its leaves change shape, its physiology hardens, and flowering becomes possible. For decades, biologists have understood this transition, called vegetative phase change, as a process governed largely by a single master switch: a tiny regulatory RNA known as miR156. Now a team at Bielefeld University has shown that the story is bigger than that. A single RNA-binding protein, AtGRP7, can hold that switch in its grip — and, remarkably, can also push plant development in directions the famous microRNA cannot explain on its own.

The research, published in BMC Plant Biology, centers on Arabidopsis thaliana, the thale cress that serves as plant biology’s laboratory mouse. The team, led by Stephan Weber, Alexander Steffen, Tino Köster, Martin Lewinski and Dorothee Staiger, set out to test whether AtGRP7 — a glycine-rich RNA-binding protein already known for its role in circadian rhythms and flowering time — also had a hand in the juvenile-to-adult transition. The answer turned out to be a resounding yes, and the way the protein exerts its influence is a textbook case of how post-transcriptional regulation, the control of RNA after it is made rather than the genes themselves, can sculpt an entire life stage.

The first clue came from plants engineered to produce excess AtGRP7. These overexpressors did something counterintuitive: they clung to their juvenile phase longer than wild-type plants, producing juvenile leaves for an extended period, while their overall rate of leaf emergence slowed. Yet when flowering time came, they bolted earlier than normal. The protein, in other words, was not simply a brake or an accelerator on development — it was decoupling two processes that usually move in lockstep, stretching one phase of life while hastening the arrival of another.

The mirror image appeared in the loss-of-function mutant, grp7-1, in which the gene is disabled. Those plants did the opposite: they abandoned their juvenile phase earlier than wild type, transitioning to adult vegetative characteristics ahead of schedule, and without any change in how fast new leaves emerged. Their flowering, however, was delayed. Delete the gene and the plant grows up faster but reproduces later; flood the plant with the protein and it stays young longer but flowers sooner. The symmetry is striking, and it establishes AtGRP7 as a genuine regulator of phase change rather than a bystander with side effects.

One obvious question followed: what about AtGRP8, the protein’s closest paralog? If two related proteins were doing the same job, removing both should have amplified the effect. It did not. The double mutant, grp7-1 grp8-2, transitioned no earlier than grp7-1 alone, indicating that AtGRP7 is the predominant player in this particular drama. In a genome full of redundant backups, this pathway apparently runs on a single named operator.

To find out what AtGRP7 was actually grabbing inside the cell, the team deployed one of the most powerful techniques in modern RNA biology: iCLIP2, an adapted version of individual-nucleotide-resolution crosslinking and immunoprecipitation. The method essentially freezes the protein to the RNA molecules it touches in living tissue, then sequences those contact points, producing a map of the protein’s direct targets in vivo. The screen returned forty-four pri-miRNAs — the long primary transcripts from which microRNAs are processed — bound by AtGRP7 inside living plants. Among them were MIR156A and MIR156C, two of the genes that produce the master regulator of phase change itself.

That binding was not incidental. When AtGRP7 was overproduced, the abundance of the MIR156A and MIR156C precursor transcripts changed, indicating that the protein alters how much raw material the cell feeds into its miR156 production line. To test whether this connection explained the developmental phenotype, the researchers crossed their overexpressor line with plants carrying MIM156, a target-mimic construct that soaks up miR156 and neutralizes it. The result: the prolonged juvenile phase of the AtGRP7 overexpressors was partially suppressed. In plain terms, at least part of the reason those plants stayed young too long is that AtGRP7 is meddling with the miR156 pathway — the very pathway biologists thought they had already mapped.

But here is where the story gets genuinely interesting, and where the paper earns its title. If AtGRP7’s effects ran entirely through miR156, then the downstream consequences should be clean and predictable. They were not. The expression of the SPL transcription factors — the family of genes that miR156 represses, and which drive the adult phase once released — was only modestly affected. A fully miR156-driven mechanism should have produced a strong, coordinated shift in SPL activity; instead the team saw a whisper. That mismatch means the protein must be working through additional, still-unidentified post-transcriptional routes, likely involving some of the other forty-two pri-miRNAs it binds, or entirely separate RNA-processing events. The canonical pathway explains part of the phenotype; the rest is unaccounted for, an open door for the next round of experiments.

The technical achievement deserves its own note. Prior to this work, the direct in vivo RNA targets of many RNA-binding proteins in plants remained stubbornly obscure — proteins were known to matter, but their contact lists were incomplete. By adapting the iCLIP2 workflow to Arabidopsis and applying it systematically to pri-miRNAs, the Bielefeld group has delivered both a biological finding and a methodological tool that other labs can immediately reuse. Every one of those forty-four bound pri-miRNAs is now a documented interaction, a starting point for anyone studying how RNA-binding proteins shape small-RNA production in plants.

Why should anyone outside a plant lab care? Because the timing of vegetative phase change is not academic trivia — it is fitness. When a plant abandons juvenility determines the architecture of its leaves, its stress tolerance, its biomass, and ultimately how much seed it makes. A protein that can lengthen youth while accelerating reproduction is, in agricultural terms, a dial with real leverage, and understanding its full circuitry is a step toward turning that dial deliberately. AtGRP7 was already known as a regulator of flowering time; this study extends its portfolio to coordinating the vegetative and reproductive halves of the plant life cycle as a whole. The juvenile phase, it turns out, is not just something plants pass through on the way to the good part. It is a stage with its own management — and AtGRP7, it appears, is one of the managers, working partly through the famous miR156 switch and partly through channels science has yet to name.

Subject of Research: Regulation of vegetative phase change in Arabidopsis by the RNA-binding protein AtGRP7

Article Title: MiR156-dependent and miR156-independent effects of the RNA-binding protein AtGRP7 on vegetative phase change in Arabidopsis

Article References: Weber, S., Steffen, A., Köster, T., Lewinski, M., & Staiger, D. (2026). MiR156-dependent and miR156-independent effects of the RNA-binding protein AtGRP7 on vegetative phase change in Arabidopsis. BMC Plant Biology. https://doi.org/10.1186/s12870-026-10084-w

Image Credits: AI Generated

DOI: 10.1186/s12870-026-10084-w

Keywords: Arabidopsis, AtGRP7, miR156, RNA-binding protein, vegetative phase change, iCLIP2, pri-miRNA, plant development, SPL transcription factors, post-transcriptional regulation, BMC Plant Biology, flowering time