The significance of this finding lies in the way it connects two domains of plant biology that have often been studied in isolation: hormone signalling and central carbon metabolism. Brassinosteroids are perceived at the cell surface by receptor complexes that ultimately inactivate a protein kinase called BIN2, a glycogen synthase kinase 3-like enzyme that functions as a central negative regulator of the brassinosteroid pathway. When brassinosteroid levels are low, BIN2 is active and phosphorylates a suite of targets, including transcription factors of the BZR1 family, thereby suppressing growth-related gene expression. When hormone levels rise, BIN2 is inhibited, its targets escape phosphorylation, and growth programmes are unleashed. The new work shows that this logic extends far beyond transcriptional control, reaching directly into the enzymatic core of sugar production.

PCK occupies a fascinating position in plant metabolism. In many plants, particularly those using C4 photosynthesis such as maize and sorghum, phosphoenolpyruvate carboxykinase catalyses the decarboxylation of oxaloacetate to release carbon dioxide and regenerate phosphoenolpyruvate, a step that concentrates carbon around the photosynthetic enzyme Rubisco and dramatically improves efficiency in hot, sunny climates. In other contexts, PCK drives gluconeogenesis, the synthesis of sugars from organic acids and lipid-derived carbon, which is essential during germination when seedlings must convert stored fat into the sugars needed to fuel early growth. In Arabidopsis, a C3 plant, PCK1 contributes to gluconeogenesis and to photosynthetic carbon metabolism, making the enzyme a versatile node at the intersection of energy production and carbon allocation.

The trail leading to the new discovery began with earlier proteomic work. A study by Tang and colleagues published in 2008 used prefractionation and two-dimensional difference gel electrophoresis to catalogue proteins whose modification changed after brassinosteroid treatment, and it revealed that PCK1 underwent dephosphorylation in response to the hormone. At the time, the observation was intriguing but mechanistically unexplained: it was not known which kinase placed the phosphate on PCK1, whether that modification affected enzyme activity, or whether the change mattered physiologically. The new study closes those gaps by identifying BIN2 as the kinase responsible and by showing that the phosphorylation event is functionally inhibitory.

A decisive piece of evidence came from a 2023 mapping effort by Kim and colleagues, who used TurboID-mediated proximity labelling coupled with mass spectrometry and phosphoproteomics to chart the signalling network of BIN2. That approach, which genetically fuses a promiscuous biotin ligase to BIN2 so that nearby proteins are labelled and can be identified, flagged PCK1 as a candidate substrate of the kinase. The new Nature Plants study builds directly on that lead, confirming that BIN2 physically interacts with PCK1, phosphorylates it at specific residues, and that this phosphorylation dampens the enzyme’s catalytic output. When brassinosteroids accumulate and BIN2 is restrained, PCK1 retains its unphosphorylated, active state, and sugar synthesis accelerates.

The physiological consequences of this regulatory module were tested across a remarkable evolutionary span. In Arabidopsis, the researchers manipulated brassinosteroid signalling and PCK1 phosphorylation status and observed corresponding changes in sugar accumulation. Strikingly, the same regulatory relationship held in maize and sorghum, two C4 grasses of enormous agricultural importance. The conservation of the BIN2–PCK1 module across such divergent species suggests that the coupling of brassinosteroid signalling to carbon metabolism is an ancient and fundamental feature of plant physiology rather than a quirk of a single lineage. For crop scientists, that conservation is encouraging news, because it implies that a single regulatory principle might be exploited to improve yield across cereals broadly.

The discovery also reframes a long-standing puzzle about how plants balance growth with carbon availability. Building new tissue requires both hormonal growth signals and an adequate supply of sugars, so plants need mechanisms that keep these two inputs in register. Recent work has shown that this coordination runs in both directions. In 2021, Zhang and colleagues reported that high sugar levels under light conditions can actually inhibit brassinosteroid signalling by enhancing BIN2-mediated phosphorylation of BZR1, providing a brake that prevents runaway growth when carbon status is already high. Conversely, the target of rapamycin pathway, a conserved nutrient-sensing network, promotes the accumulation of BZR1 in response to sugar, as shown in a 2016 study, thereby ensuring that sugar availability feeds positively into brassinosteroid signalling output.

Starvation adds a further layer of control. A 2025 study by Zhang and colleagues demonstrated that the ubiquitin ligase UPL3 mediates the degradation of BZR1 when nutrients run low, driving growth arrest and improving seedling survival under starvation stress. Taken together with the new findings, a coherent picture emerges: brassinosteroid signalling sits at the hub of a bidirectional dialogue with carbon metabolism, promoting sugar synthesis through PCK1 when conditions favour growth, while being restrained by sugar feedback and dismantled when carbon becomes scarce. The BIN2 kinase emerges as a shared bottleneck in this dialogue, phosphorylating both transcriptional regulators and metabolic enzymes to enforce the plant’s overall growth-versus-survival decision.

From a biotechnological standpoint, the implications are considerable. Enhancing PCK activity or reducing its inhibitory phosphorylation could, in principle, increase the efficiency with which crops convert carbon dioxide into sugars, the raw material for grain, biomass, and ultimately yield. Because the module operates in maize and sorghum, engineering or breeding strategies that favour the dephosphorylated, active state of PCK could be pursued in crops where even modest gains in photosynthetic efficiency translate into substantial harvest improvements. The finding also offers a mechanistic explanation for why brassinosteroid-related traits, such as enhanced seedling vigour, often correlate with improved performance in the field: the hormone is not merely stretching cells but also feeding the metabolic engine that powers growth.

As with any major advance, questions remain. The precise kinetic consequences of PCK1 phosphorylation at each target residue, the relative contributions of gluconeogenesis versus photosynthetic carbon concentration to the observed sugar increases, and the tissue-specific architecture of the BIN2–PCK1 module in developing seeds and leaves are all ripe for further study. It will also be important to determine whether tuning the module carries trade-offs, since unchecked sugar production could alter source–sink relationships within the plant. Nevertheless, by identifying a direct biochemical link between a growth hormone and a sugar-synthesising enzyme, the study transforms our understanding of how plants coordinate the decision to grow with the metabolic capacity to sustain it, and it hands crop engineers a concrete molecular target in the quest for more productive plants.

Subject of Research: Brassinosteroid hormone regulation of sugar synthesis through BIN2-mediated phosphorylation of phosphoenolpyruvate carboxykinase in plants

Article Title: Brassinosteroids boost sugar production by inhibiting PCK phosphorylation

Article References: Brassinosteroids boost sugar production by inhibiting PCK phosphorylation. (2026). Nature Plants, 12(9), 1673-1674. https://doi.org/10.1038/s41477-026-02378-6

Image Credits: AI Generated

DOI: 10.1038/s41477-026-02378-6

Keywords: brassinosteroids, BIN2 kinase, PCK, phosphorylation, sugar synthesis, gluconeogenesis, C4 photosynthesis, Arabidopsis thaliana, maize, sorghum, plant signalling, carbon metabolism