When trees grow sideways: Genetic control of branch angles for smarter orchards
image: Representative ‘Stanley’ OP and LAZY1-antisense Line 4 on ‘Myrobalan’ rootstock trained into planar systems. (A) Espalier training. (B) SSA training. Note that ‘Stanley’ OP trees trained as Espalier and SSA grew past the top (fourth) trellis wire by August 2021 while the LAZY1-antisense trees grew along it and downwards. ‘Myro’ indicates ‘Myrobalan’ rootstock.
Credit: Horticulture Research
Optimizing tree architecture is a long-standing challenge in fruit production, as branch orientation directly affects light interception, labor requirements, and yield efficiency. This study shows that silencing a single gravity-related gene, LAZY1, can permanently reshape tree growth patterns. By reducing LAZY1 expression, researchers produced plum trees with wider branch angles, outward and wandering growth trajectories, and more open canopies. These architectural changes were stable across years, environments, and rootstocks, and did not compromise branch strength or fruit formation. The findings demonstrate a genetic strategy for redesigning tree form from within, offering a long-term alternative to labor-intensive pruning, tying, and growth-regulator applications.
In modern high-density orchards, tree shape is critical for maximizing light capture, improving fruit quality, and reducing management costs. However, many fruit trees naturally grow upright, requiring repeated pruning, branch bending, or chemical treatments to control canopy structure. These practices are labor-intensive, costly, and often only temporarily effective. Previous research has shown that branch angle is largely genetically controlled, particularly through pathways involved in gravity perception and auxin transport. Among these regulators, LAZY1 plays a central role in directing upward growth responses. Based on these challenges, there is a clear need to investigate genetic approaches that can permanently modify branch orientation and optimize tree architecture.
Researchers from Michigan State University, the U.S. Department of Agriculture Agricultural Research Service, and the University of Maryland reported (DOI: 10.1093/hr/uhaf106) on 16 April 2025 in Horticulture Research, that suppressing the LAZY1 gene dramatically alters branch orientation in European plum (Prunus domestica). Through long-term greenhouse and field experiments, the team demonstrated that LAZY1-silenced trees developed wider branch angles and non-upright growth patterns that improved canopy openness. Published online in April 2025, the study provides one of the most comprehensive real-world evaluations of genetically modified tree architecture to date.
The researchers generated multiple transgenic plum lines carrying an antisense construct designed to reduce LAZY1 expression. Molecular analyses confirmed that the construct specifically targeted LAZY1 without affecting closely related genes involved in root or shoot orientation. Across six effective lines, LAZY1 expression was significantly reduced, resulting in consistently wider petiole and branch angles compared with control trees.
Field and greenhouse observations showed that LAZY1-silenced branches no longer exhibited strong upward growth in response to gravity. Instead, branches followed wandering, arching, or outward trajectories, producing more open and horizontally distributed canopies. Importantly, these traits were maintained when trees were grafted onto standard commercial rootstocks, indicating that the altered architecture was intrinsic to the scion.
To assess practical relevance, the team trained trees in two planar orchard systems—espalier and super slender axe. Compared with controls, LAZY1-silenced trees were easier to constrain below trellis height, showed reduced apical dominance, and required less aggressive pruning. Mechanical testing revealed that branch stiffness and load-bearing capacity were not reduced, despite changes in wood material properties. Although some lines displayed seasonal leaf chlorosis and reduced photosynthesis, all lines produced flowers and fruit with quality traits remaining within normal ranges.
“Tree architecture has traditionally been managed with intensive labor over many years,” said one of the study’s senior authors. “Our results show that by modifying how a tree responds to gravity at the genetic level, it is possible to create growth habits that naturally align with modern orchard systems. While some physiological trade-offs still need to be addressed, this approach opens the door to designing trees that are fundamentally easier to train, maintain, and manage throughout their productive lifespan.”
Genetic control of branch orientation could significantly reduce labor inputs in fruit production while improving canopy uniformity and light distribution. Trees with inherently wider branch angles may be better suited for high-density planting systems and mechanized orchard management. Beyond commercial fruit production, the wandering and weeping growth habits observed in LAZY1-silenced trees may also hold value for ornamental horticulture. More broadly, this work highlights the potential of targeting gravity-response pathways to redesign perennial crop architecture, offering a foundation for future breeding and biotechnological strategies aimed at more efficient and sustainable orchard systems.
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References
DOI
Original Source URL
https://doi.org/10.1093/hr/uhaf106
Funding information
Funding for this work was provided by Michigan State University, The Michigan State Horticultural Society, The United States Department of Agriculture National Institute of Food and Agriculture HATCH project 1013242 (C.A.H.), MSU AgBioResearch Project GREEEN grant GR18-03, and the Agriculture and Food Research Initiative Competitive Grants Program, grant no. WVAW-2011-04220, from the USDA National Institute of Food and Agriculture (C.D.).
About Horticulture Research
Horticulture Research is an open access journal of Nanjing Agricultural University and ranked number one in the Horticulture category of the Journal Citation Reports ™ from Clarivate, 2023. The journal is committed to publishing original research articles, reviews, perspectives, comments, correspondence articles and letters to the editor related to all major horticultural plants and disciplines, including biotechnology, breeding, cellular and molecular biology, evolution, genetics, inter-species interactions, physiology, and the origination and domestication of crops.