The ABCB family belongs to the larger superfamily of ATP-binding cassette (ABC) transporters, membrane proteins found from bacteria to humans that burn cellular energy in the form of ATP to pump molecules across membranes. In plants, ABC transporters ferry an astonishing variety of cargo: defense compounds, heavy-metal chelators, waxes and, critically, phytohormones. Within this superfamily, the B subgroup—full-length transporters containing both nucleotide-binding domains and transmembrane domains—has attracted particular attention because several of its members in the reference plant Arabidopsis thaliana are proven hormone movers. AtABCB1 and AtABCB19, for instance, are celebrated auxin efflux carriers that help establish the localized auxin gradients sculpting virtually every organ of the plant, and recent structural work has revealed that AtABCB19 also exports brassinosteroids, the steroid hormones that drive stem elongation, vascular development and stress resilience.

What happens to these functions in crop plants with larger, more complex genomes has been far less clear. The Brassica genus, which includes cabbage, broccoli, oilseed rape and choy sum, descended from a common ancestor with Arabidopsis through extensive whole-genome triplication followed by diploidization and rearrangements, meaning that for every Arabidopsis ABCB gene there may be several Brassica relatives whose functions have diverged, specialized or been lost. Floting Chinese cabbage is an economically important vegetable in southern China, and its tall, succulent stalk is the product of vigorous cell elongation intimately tied to brassinosteroid and auxin action—making it an ideal system in which to ask what the ABCB repertoire is doing.

To answer that question, the team carried out a genome-wide survey of the B. rapa var. parachinensis genome, an effort made feasible by a recent high-continuity genome assembly of the species. Using rigorous bioinformatic screening, they identified 36 BraABCB genes and constructed phylogenetic trees that placed them into four evolutionary groups, consistent with the canonical architecture of ABCB families described in other angiosperms. Conserved domain analysis confirmed that the predicted proteins carry the hallmarks expected of functional transporters:Walker A and Walker B motifs and the signature C-loop within the nucleotide-binding domains, together with the membrane-spanning α-helices that form the translocation pathway. When Arabidopsis ABCB proteins were included in the phylogeny, the BraABCB27 and BraABCB28 proteins clustered tightly with AtABCB1 and AtABCB19, immediately flagging them as the closest functional relatives of the best-characterized hormone transporters in any plant.

Evolutionary forensics added context to this inventory. The researchers mapped each BraABCB gene to its position on the ten chromosomes of the species and examined collinearity—the synteny between genomic regions—to trace how the family expanded. Synonymous and nonsynonymous substitution rates (Ka/Ks) calculated for duplicated gene pairs told a story of constraint: with Ka/Ks values well below one, most BraABCB paralogs have been maintained under purifying selection, meaning that the protein-coding sequences have been preserved largely intact since their duplication. In other words, the family did not balloon through sloppy replication but rather through ancient genome duplication events whose products the plant has carefully conserved—an evolutionary signature typically associated with genes that matter.

But conservation at the sequence level is only a hypothesis about function; the real test lies in where the genes are switched on and what the proteins do. The group focused its experimental attention on Group IV, the clade containing the AtABCB1/19 relatives. Mining the promoter regions upstream of these genes revealed a rich catalog of cis-regulatory elements implicated in hormone responsiveness and abiotic stress, including motifs associated with drought, heat, and both auxin and brassinosteroid signaling. To put these predictions to the test, the researchers grew choy sum seedlings under several perturbations—drought stress, elevated temperature, exogenous application of the bioactive brassinosteroid brassinolide, and treatment with the primary natural auxin, indole-3-acetic acid—and quantified the expression of selected Group IV BraABCB genes by reverse-transcription quantitative PCR using the standard 2^-ΔΔCT method. The results were striking in their diversity: individual family members responded differently and often in opposite directions to the same stimulus, indicating that the Brassica expansion of this family is not mere redundancy but a differentiated toolkit, with distinct transporters likely deployed in different tissues, developmental stages and environmental contexts.

Subcellular localization supplied a further piece of the puzzle. Because ABCB transporters must sit in a membrane to move hormones across it, the team fused Group IV BraABCB proteins to fluorescent reporters and expressed the constructs to determine where the fusion proteins accumulated in living cells. The analyses showed predominant localization to the plasma membrane, exactly where an efflux carrier engaged with extracellular signaling and long-distance hormone movement would be expected to reside. This placement also matters for a second reason: the brassinosteroid receptor itself, BRI1 (BRASSINOSTEROID-INSENSITIVE 1), is a leucine-rich repeat receptor kinase embedded in the plasma membrane, discovered in the 1990s as the cell-surface sensor for the steroid hormones. If ABCB transporters share membrane real estate with BRI1, opportunities for physical and functional crosstalk multiply.

That possibility is precisely where the new study makes its most intriguing contribution. In Arabidopsis, a regulatory protein called TWISTED DWARF1—an immunophilin-like co-chaperone—has been shown to associate physically with BRI1 and to be required for the full activity of the ABCB1- and ABCB19-mediated auxin transport machinery; mutations in the corresponding gene produce pleiotropic, hormone-defective growth phenotypes, and the interplay between ABCB transporters and BRI1-related membrane complexes has become a model of how transport and signaling are coordinated at the cell surface. Using bimolecular fluorescence complementation (BiFC), a technique in which two proteins are fused to halves of a fluorescent protein so that a physical interaction brings the halves together and restores fluorescence, together with a split-ubiquitin yeast two-hybrid assay that is better suited to membrane proteins, the Guangzhou University team tested whether the choy sum homologs could engage BRI1-related proteins. The answer was yes: BraABCB27 and BraABCB28, the two closest relatives of AtABCB1 and AtABCB19, showed detectable physical associations with BRI1-related proteins in both systems.

The authors are careful in their claims—and appropriately so. Detecting an association is not the same as demonstrating a transport function, and the study stops short of showing that BraABCB27 and BraABCB28 actually pump brassinosteroids or auxin in planta. What the work provides instead is a complete, experimentally grounded framework: a full inventory of 36 genes with their evolutionary history, a demonstration that Group IV members are stress- and hormone-responsive, confirmation of plasma-membrane targeting, and two strong candidates whose interaction with BRI1-related proteins now invites direct functional interrogation. The logical next steps—CRISPR knockout or overexpression of BraABCB27 and BraABCB28, followed by measurements of stalk elongation, brassinosteroid distribution and auxin gradients—would test whether these transporters are genuinely part of the machinery that regulates the trait for which choy sum is grown.

The broader implications reach beyond a single vegetable. Brassinosteroids have become a major focus of crop engineering because of their capacity to enhance yield, stress tolerance and architectural traits, and recent structural biology has revealed the atomic details of how the Arabidopsis ABCB1 and ABCB19 transporters export these steroids. Whether the same transport-signaling coupling exists in Brassica crops—and how the triplicated genome has diversified it—remains open, but this study supplies the map on which such questions can now be asked. For breeders seeking taller stalks, denser flowering or improved drought resilience in flowering Chinese cabbage, the BraABCB family just moved from anonymous genomic baggage to a shortlist of actionable targets. And for plant biologists more generally, the finding that ABCB-BRI1 associations are conserved in a distantly related crop reinforces an emerging picture: in plants, hormone transport and hormone perception are not separate layers of regulation but physically intertwined systems working at the same membrane, in the same cells, at the same time.

Brassinosteroids regulate nearly every stage of plant development. They influence cell expansion, vascular differentiation, root and shoot growth, reproductive development, and the plant’s ability to adjust to environmental stress. Their effects begin when a brassinosteroid binds to a receptor kinase known as BRI1, located in the plasma membrane. BRI1 is not simply an on-and-off molecular switch. It functions as part of a receptor system whose activity depends on ligand binding, receptor conformation and the recruitment of a co-receptor, most notably BAK1. The resulting signaling complex activates a phosphorylation cascade that ultimately changes gene expression and growth patterns.

The difficulty lies in the chemistry. Brassinosteroids share a steroid framework, but small differences in hydroxylation, oxidation, stereochemistry and side-chain structure can strongly affect their biological activity. Some compounds act as powerful agonists, while others bind less efficiently or produce weaker physiological responses. Until now, these differences have often been described through isolated structures or activity measurements rather than through a unified explanation of how the receptor reads chemical information. The new study seeks to connect those observations by examining the physical principles governing recognition across the brassinosteroid family.

The researchers describe BRI1-family receptors as molecular sensors that combine broad chemical tolerance with highly selective signaling control. Rather than recognizing a single rigid molecular shape, the receptor’s binding pocket appears capable of accommodating related brassinosteroids through a network of complementary interactions. These include hydrogen bonds involving steroid hydroxyl groups, hydrophobic contacts with the steroid core and interactions that position the ligand’s side chain within the receptor. The balance among these contacts determines how effectively a compound stabilizes the receptor in a signaling-competent state.

This distinction between binding and activation is crucial. A molecule may fit into a receptor pocket without producing the structural rearrangement required for efficient signal transmission. In BRI1, ligand recognition is linked to changes in the extracellular portion of the receptor that promote association with BAK1. Once the co-receptor is recruited, the intracellular kinase domains are brought into an arrangement that enables reciprocal phosphorylation. This molecular choreography converts an extracellular chemical event into an intracellular response. The study’s framework emphasizes that brassinosteroid activity depends not only on whether a compound binds, but also on how it reshapes the receptor complex.

The work also helps explain why closely related receptors within the BRI1 family can respond differently to the same hormone-like molecules. Family members may preserve the overall architecture of the ligand-binding site while differing at selected residues that control pocket volume, polarity and flexibility. Such substitutions can alter the orientation of a brassinosteroid or change the energetic cost of receptor rearrangement. As a result, one receptor may favor a particular steroid structure, whereas another may recognize the same compound weakly or translate its binding into a different signaling output.

By bringing these features together, the researchers provide a way to interpret brassinosteroid recognition as a dynamic process rather than a simple lock-and-key interaction. The receptor must accommodate chemical variation while maintaining enough structural precision to activate downstream signaling. This balance may allow plants to use a broad hormonal vocabulary without requiring a completely separate receptor for every steroid. It also offers a molecular explanation for why modifications at seemingly minor positions on the brassinosteroid scaffold can produce major differences in growth-promoting activity.

The findings could have implications well beyond basic plant physiology. Brassinosteroid signaling is already of interest in agriculture because it affects biomass accumulation, architecture, fertility and stress resilience. A clearer understanding of receptor selectivity could support the design of synthetic brassinosteroid analogues with tailored properties. Instead of searching only for compounds that produce the strongest response, researchers may be able to develop molecules that selectively activate particular receptor family members, work at lower concentrations or deliver desirable growth effects while minimizing unwanted developmental changes.

The study also highlights the broader value of receptor-kinase biology in plants. Many plant hormones are perceived by membrane receptors that must recognize chemically diverse signals and convert them into context-dependent responses. The BRI1 system offers an especially clear model for studying how ligand chemistry, protein motion and co-receptor assembly are integrated. By defining the principles that govern brassinosteroid recognition, the research provides a foundation for predicting how new molecules might interact with plant receptors and for understanding how evolutionary changes in receptor proteins can reshape hormone sensitivity.

In a field increasingly focused on climate-resilient crops and precision agriculture, that predictive capacity could become highly valuable. Plants cannot escape drought, heat, nutrient limitation or disease, but they can adjust growth through interconnected signaling networks. Manipulating brassinosteroid perception may eventually help fine-tune those responses without broadly disrupting development. The new mechanistic framework does not by itself create a new crop technology, but it supplies the kind of molecular map needed to move from trial-and-error hormone treatments toward rational design. It transforms brassinosteroid recognition from a collection of individual receptor–ligand observations into a more coherent story about chemical diversity, protein dynamics and plant growth control.

Subject of Research: Recognition and signaling mechanisms of chemically diverse brassinosteroids by BRI1-family receptor kinases in plants

Article Title: A mechanistic framework for the recognition of chemically diverse brassinosteroids by BRI1-family receptor kinases

Article References: Caregnato, A., Chen, H., Kvasnica, M. et al. A mechanistic framework for the recognition of chemically diverse brassinosteroids by BRI1-family receptor kinases. Nat. Plants (2026). https://doi.org/10.1038/s41477-026-02346-0

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41477-026-02346-0

Keywords: brassinosteroids, BRI1, receptor kinases, plant hormones, plant growth, hormone signaling, BAK1, ligand recognition, molecular biology, crop science

The role of reactive oxygen species has evolved from being considered merely harmful byproducts of cellular metabolism to being recognized as essential signaling molecules in plants. When subjected to abiotic stresses, plants experience cellular oxidative stress, leading to the generation of ROS. Contrary to the previous perception, these molecules play a dual role; while they can cause damage to cellular components, they also activate signaling pathways that enhance stress tolerance. This critical balance between ROS accumulation and detoxification mechanisms forms the crux of plant responses to adverse environmental conditions.

In the context of abiotic stress, hormonal signaling becomes indispensable. Plant hormones, including abscisic acid (ABA), salicylic acid (SA), jasmonic acid (JA), and ethylene, orchestrate a wide array of physiological responses. For example, ABA is pivotal in regulating stomatal closure during drought conditions, minimizing water loss. Meanwhile, SA and JA are involved in orchestrating defense responses against environmental stressors. The dynamic interplay between ROS and these hormones creates a finely tuned system that facilitates a plant’s adaptation and resilience against various abiotic challenges.

The groundbreaking research by Bali offers insights into how ROS not only function as secondary messengers but also interact with various plant hormones to modulate plant responses. One critical finding suggests that under conditions of oxidative stress, certain hormones can regulate the expression of genes involved in ROS scavenging pathways, effectively enhancing a plant’s ability to mitigate damage. This suggests a feedback mechanism where the coordination between ROS production and hormonal signaling can significantly influence a plant’s overall health and reproductive success.

Another interesting aspect highlighted in the study is the role of signaling cross-talk between different types of stress. Plants often encounter multiple stressors simultaneously. For instance, drought conditions can invoke not only water-deficit stress responses but also alter disease susceptibility. Bali emphasizes that understanding how ROS and hormone signaling networks interact can reveal strategies for breeding more resilient crop varieties. This integration of knowledge could lead to innovative agricultural practices that ensure food security against the backdrop of climate change.

Bali’s research sheds light on specific signaling pathways that illustrate this integration. In the face of drought, for example, the activation of ABA leads to the accumulation of ROS, which in turn can promote the expression of drought-responsive genes. This axis between ABA and ROS generation not only enhances the plant’s tolerance to drought but also places it in a better position to respond to other stresses concurrently. This multifaceted approach towards understanding plant resilience is what sets this research apart from traditional single-factor studies.

Furthermore, the research argues that this relationship may also extend to nutrient signaling, where deficiencies can produce ROS that initiate hormonal responses aimed at promoting nutrient uptake and utilization. The implication here is profound, as it opens up avenues for exogenous application of certain hormones or plant growth regulators under specific stress conditions to enhance ROS management. This highlights a promising area for future research into precision agriculture, where tailored treatments could boost plant health and productivity.

One of the most exciting implications of this study is the potential for biotechnology applications. By altering ROS and hormone signaling pathways, scientists could engineer crops that not only withstand but thrive under stress conditions. Genetic modifications aimed at enhancing ROS scavenging capabilities or improving hormone sensitivity could revolutionize agricultural practices. This aligns with a growing focus on sustainable farming methods that prioritize resilience, yield, and environmental stewardship.

Moreover, Bali’s findings have implications beyond just crop science; they could also inform conservation efforts for natural plant ecosystems. As climate variability continues to escalate, understanding plant stress responses will be crucial for preserving biodiversity. The mechanisms elucidated in this research can serve as a foundation for enhancing the resilience of endangered plant species faced with habitat changes.

The urgency of this research cannot be overstated. As global temperatures rise and climate change continues to alter weather patterns, the effects on agriculture and ecosystems represent a significant challenge for humanity. Innovations driven by studies like Bali’s provide vital insights that could lead to effective strategies to bolster plant resilience, thus safeguarding our food supply and preserving the environment.

Standing at the crossroads of advanced agricultural science, the integration of ROS and plant hormone signaling presents a promising frontier. Acknowledging the complexities of these interactions not only enhances our understanding of plant biology but is also pivotal for developing strategies to mitigate the impending challenges posed by climate change and other environmental stressors.

As we delve deeper into these research narratives, it becomes increasingly clear that the synergy between reactive oxygen species and hormonal signaling represents a delicate yet powerful mechanism that underpins plant survival. The ongoing investigation into these signaling networks will undoubtedly enrich our approaches to agriculture and conservation, ultimately bridging the gap between scientific discovery and practical application. By leveraging these insights, we can aspire to cultivate a more resilient and sustainable future.

By continuing these explorations, the scientific community reinforces its commitment to developing holistic approaches that address the multifaceted challenges of agricultural resilience in an era of uncertainty. Not only does this research provide a glimpse into the remarkable adaptability of plants, but it also underscores our responsibility to harness this knowledge for the greater good of our planet and its inhabitants.

Subject of Research: Integration of reactive oxygen species and plant hormone signaling in response to abiotic stress.

Article Title: Integrating ROS and plant hormone signaling in response to abiotic stress.

Article References: Bali, A.S. Integrating ROS and plant hormone signaling in response to abiotic stress. Discov. Plants 2, 355 (2025). https://doi.org/10.1007/s44372-025-00440-9

Image Credits: AI Generated

DOI: https://doi.org/10.1007/s44372-025-00440-9

Keywords: abiotic stress, reactive oxygen species, plant hormones, drought, salinity, climate change, agricultural resilience, biotechnology, food security, conservation.

At the core of Dr. Strader’s research is the intricate hormonal network regulated by auxin, a pivotal phytohormone that orchestrates diverse developmental processes in plants. Unlike animals, which follow genetically predetermined developmental schedules, plants exhibit remarkable plasticity, adapting their growth cycles based on environmental stimuli. Auxin’s regulation of cell division, elongation, and differentiation enables this flexibility, allowing plants to optimize resource allocation and survival strategies amid shifting conditions such as temperature fluctuations and nutrient variability.

Strader’s laboratory adopts a multidisciplinary methodology, weaving together approaches from molecular biology, biochemistry, genetics, systems biology, and synthetic biology to decipher the precise molecular mechanisms underpinning auxin signaling pathways. By employing cutting-edge technologies—from high-resolution structural biology to advanced biophysical assays—her team probes the dynamic protein interactions and regulatory feedback loops that modulate auxin transport and signal transduction. This integrative strategy aims to map the comprehensive auxin regulatory network, revealing nodes amenable to engineering for enhanced plant resilience.

The environmental responsiveness of auxin pathways holds profound implications for agricultural innovation. As global temperatures rise and arable land faces increased stress from extreme weather events, there is urgent need to develop crops with robust stress tolerance and efficient nutrient utilization. Strader’s research delves into how external factors such as thermal stress and soil nutrient composition influence auxin synthesis and distribution, thereby affecting developmental decisions like flowering time and root architecture. These insights form the scientific substrate for designing bioengineered plants capable of sustained productivity under adverse environmental conditions.

Beyond fundamental discovery, Strader is deeply committed to translational science. Her group is pioneering the application of auxin pathway modulation to create crop varieties that maintain reproductive competence despite elevated nighttime temperatures, a known threat to yield stability. Furthermore, her investigations into the hormonal crosstalk regulating nitrogen use efficiency have yielded promising strategies to reduce dependency on synthetic fertilizers, thereby promoting sustainable agriculture practices that mitigate environmental pollution and greenhouse gas emissions.

The Salk Institute’s supportive research environment plays a pivotal role in facilitating Strader’s ambitious scientific agenda. The Institute’s focus on interdisciplinary collaboration and freedom from conventional institutional distractions enables sustained intellectual pursuit and rapid translation of discoveries into practical solutions. Strader highlights the unique culture at Salk that fosters dynamic interactions across biology, chemistry, physics, and computational sciences, accelerating the development of innovative approaches to plant biology challenges.

Strader’s academic journey traces a trajectory of rigorous training and impactful contributions. She completed her undergraduate studies in agronomy at Louisiana State University, followed by a PhD in molecular plant sciences at Washington State University. Her postdoctoral work at Rice University further honed her biochemical and cell biology expertise, laying the foundations for her later scientific breakthroughs. Over her career, Dr. Strader has garnered prestigious honors, including a fellowship from the American Association for the Advancement of Science and the National Science Foundation’s Early Faculty Career Development Award. Her recognition as one of the 25 Inspiring Women in Plant Biology by the American Society of Plant Biologists underscores her influence and leadership in the field.

The importance of auxin in regulating plant development cannot be overstated. This small, yet powerful hormone influences processes ranging from embryogenesis to organogenesis, mediating adaptive responses to environmental stimuli. Strader’s research elucidates how auxin’s spatial and temporal gradients are established and maintained through tightly controlled biosynthesis, conjugation, transport, and signaling mechanisms. Elucidating these complex layers of regulation is fundamental for understanding phenotypic plasticity in plants—an evolutionary advantage that could be harnessed for designing crops resilient to climate change.

Technological advancements in synthetic biology are integral to Strader’s strategy for enhancing crop traits. By engineering synthetic auxin-responsive circuits and optimizing hormone receptor functions, her group is exploring ways to fine-tune developmental outputs with high precision. This synthetic approach holds promise for creating plants with tailored growth patterns, optimized resource use, and improved resistance to biotic and abiotic stressors, revolutionizing the paradigm of crop improvement.

Strader’s interdisciplinary framework extends to collaborations with computational biologists and systems scientists, who model the complex auxin regulatory networks and predict outcomes of genetic or environmental perturbations. These predictive models inform targeted experiments and accelerate the iterative cycle of hypothesis testing and validation. Through systems-level understanding, her work bridges molecular mechanisms to organismal phenotypes and ecological relevance, contributing to the broader goal of sustainable ecosystem management.

Moreover, Strader’s research aligns synergistically with the Salk Institute’s Harnessing Plants Initiative, a visionary program dedicated to reimagining plant productivity and resilience in the face of a rapidly changing climate. By integrating her expertise into this initiative, Strader’s research promises to elevate efforts toward breeding and engineering crops that not only survive but thrive under environmental stress, represented by extreme heat, drought, and nutrient-poor soils.

In summary, Dr. Lucia Strader’s appointment at the Salk Institute marks a momentous advancement in plant biology, combining deep mechanistic insights with a mission-driven focus on agricultural sustainability. Her work on auxin biology and environmental signal integration has the potential to transform how scientists and farmers address food security under the looming pressures of global climate change. The fusion of innovative molecular techniques and practical application sets the stage for groundbreaking discoveries and agricultural technologies that may safeguard crop yields and support human wellbeing well into the future.

Subject of Research: Plant hormone biology focusing on auxin signaling and its role in plant development and environmental adaptability.

Article Title: Dr. Lucia Strader Joins Salk Institute to Pioneer Molecular Insights and Applications in Plant Hormone Biology

News Publication Date: August 20, 2025

Web References:

• Salk Institute: www.salk.edu
• Harnessing Plants Initiative: https://www.salk.edu/harnessing-plants-initiative/
• Gerald Joyce profile: https://www.salk.edu/scientist/gerald-joyce/

Image Credits: Credit: Salk Institute

Keywords: Plant sciences, Plant signaling, Plant biochemistry, Plant biotechnology, Plant development, Plant genetics, Plant physiology, Plant products, Plants, Climate change, Climate change effects, Agriculture, Sustainable agriculture