Evolution of the DELLA gene family in plants and functional characterization of PmDELLA-like in the regulation of plant architecture in Prunus mume
This study elucidates the evolutionary history of the DELLA gene family across 324 plant species and demonstrates that the *Prunus mume* gene *PmDELLA-like* functions as a key regulator of plant architecture by integrating gibberellin signaling with light-responsive and cell elongation pathways to control growth and branching in woody plants.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
Plants are masters of shape-shifting, constantly adjusting their height and branching to compete for sunlight or survive harsh conditions. At the heart of this flexibility lies a sophisticated internal communication system driven by hormones, specifically a group called gibberellins. Think of gibberellins as the plant's growth accelerator; when levels are high, stems stretch, cells divide, and the plant reaches for the sky. However, nature rarely allows unchecked acceleration. To prevent a plant from growing too tall or too fast, it employs a set of molecular brakes known as DELLA proteins. These proteins act as central switches, holding growth in check until the hormone signal tells them to step aside. When gibberellin is present, it binds to a receptor that marks the DELLA proteins for destruction, effectively releasing the brakes and allowing the plant to grow. This delicate balance between the accelerator and the brake determines the final architecture of a tree or flower, influencing everything from crop yields to the aesthetic form of an ornamental garden.
For decades, scientists understood how this system worked in model plants like Arabidopsis, but the full story of how these molecular brakes evolved across the entire tree of life remained incomplete. A new study by researchers at Qingdao Agricultural University and their colleagues has traced the history of these proteins across hundreds of millions of years and in hundreds of different species. By examining the genetic blueprints of 324 distinct plant species, ranging from ancient mosses to modern flowering trees, the team reconstructed the evolutionary journey of the DELLA family. They discovered that these proteins did not appear fully formed but evolved through three distinct stages, mirroring the step-by-step assembly of the plant's growth-control machinery. In the earliest land plants, the molecular "brake" was a loose, variable structure that functioned independently of the hormone signal. As vascular plants evolved, this structure hardened into a precise, conserved shape that could finally interact with the gibberellin receptor, creating the modern on-off switch. Later, as flowering plants diversified, the family split into two distinct lineages: one that retained the classic, hormone-sensitive brake, and another that evolved into a permanent, unyielding brake that could not be removed by the hormone.
The researchers then turned their attention to the Chinese plum, Prunus mume, a tree cherished for over 3,000 years for its early spring blossoms and elegant, sprawling branches. Despite its horticultural value, breeding compact, highly branched varieties for bonsai and pot culture has been difficult because the genetic rules controlling its shape were unknown. The team identified a specific gene in the plum tree, which they named PmDELLA-like, that belonged to the second, permanent-brake lineage. Unlike the classic DELLA proteins, this version had lost the ability to bind to the gibberellin receptor, meaning it could not be destroyed by the hormone signal. To understand what this gene actually does, the scientists performed a series of experiments. They first confirmed that the gene is most active in the growing tips of the tree and the young leaf buds, the very places where height and branching are determined. Surprisingly, even though the protein itself cannot be degraded by gibberellin, the gene's activity increases when the plant is sprayed with the hormone, suggesting the plant uses it as a feedback mechanism to fine-tune its growth.
To see the gene in action, the researchers introduced the PmDELLA-like gene into poplar trees, a fast-growing model species, to observe what happened when the tree was forced to produce extra amounts of this permanent brake. The results were dramatic. The modified poplars grew significantly shorter than their normal counterparts, with much shorter distances between their leaves. Instead of a single, tall trunk, the trees became bushy, sprouting a dense network of side branches. Under a microscope, the cells in the stems of these modified trees were visibly smaller and more tightly packed, indicating that the gene was successfully inhibiting cell expansion and division. The scientists also measured the hormone levels inside these trees and found that the endogenous gibberellin content had dropped. This suggests that the presence of the permanent brake triggers the plant to reduce its own production of the growth hormone, creating a self-reinforcing cycle of compactness.
Digging deeper into the genetic changes caused by this gene, the team analyzed the entire set of active genes in the modified poplar stems. They found that the gene did not just act as a simple stop sign; it rewired the plant's internal clock and its response to light. The genes that control the daily circadian rhythm and those that help the plant sense light intensity were significantly altered. This indicates that the PmDELLA-like protein acts as a central hub, integrating signals about the time of day and the quality of light with the hormone signals to decide how the tree should grow. By connecting these different systems, the gene allows the plant to coordinate its height and branching in a way that is perfectly suited to its environment. The study concludes that while the classic DELLA proteins act as the primary switch for growth, this DELLA-like variant serves as a sophisticated regulator that fine-tunes the plant's architecture by balancing hormone levels with light and time cues. These findings offer a new roadmap for breeders who wish to develop ornamental trees with compact, bushy forms, providing a specific genetic target to manipulate the shape of woody plants without relying on traditional, often unpredictable, breeding methods.
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