Naringin has been studied for decades as a pharmaceutical treasure. It belongs to the flavanone glycosides, a family of plant secondary metabolites linked in the scientific literature to anti-inflammatory, antioxidant, and metabolic benefits, and it is the dominant bitter compound in the rind and flesh of Huajuhong fruit, a traditional Chinese medicine material. The enzymes that build naringin step by step were already well characterized: phenylalanine ammonia-lyase, chalcone synthase, flavone synthase, and two glycosyltransferases that decorate the flavanone backbone with sugars. What remained murky was the regulatory layer above those enzymes, the machinery that decides when the whole pathway should be switched on in response to environmental and hormonal cues.

The research team, led by Genlin Mao, Diyang Qiu, and Ruiyi Fan from the Guangdong Academy of Agricultural Sciences and Jingchu University of Technology, focused on jasmonate, a plant hormone best known for coordinating defense responses against herbivores and pathogens. When they treated pomelo seedlings with methyl jasmonate, a cell-permeable jasmonate analog widely used as an elicitor, naringin levels surged 3.45-fold. Crucially, the gene encoding CgMYC2, a member of the basic helix-loop-helix transcription factor family, responded even faster, rising 6.6-fold before the peak expression of the five core biosynthetic genes. That timing mattered: the putative regulator switched on before its presumed targets, exactly the sequence expected of a genuine upstream controller rather than a downstream passenger.

To place CgMYC2 within the canonical jasmonate signaling cascade, the researchers turned to protein interaction assays. In the standard model of jasmonate perception, the hormone is sensed by a receptor complex that then degrades members of the JAZ family of repressor proteins. Those JAZ proteins, when present, physically clamp down on MYC transcription factors and prevent them from activating genes. Using pull-down and co-immunoprecipitation experiments, the team confirmed that CgMYC2 directly interacts with CgJAZ3, a JAZ repressor from pomelo. This interaction anchors CgMYC2 firmly in the jasmonate pathway: when jasmonate levels rise, JAZ proteins are destroyed, CgMYC2 is released, and the biosynthetic genes can be transcribed.

The next question was whether released CgMYC2 actually touches the DNA of the naringin pathway genes. The answer came from a battery of complementary techniques. Yeast one-hybrid assays confirmed binding to the promoter of Cg1,2RhaT, the rhamnosyltransferase that performs the final sugar-transfer step in naringin synthesis. Electrophoretic mobility shift assays went further, demonstrating that CgMYC2 binds directly, and in a G-box-dependent manner, to the promoters of all five core biosynthetic genes: CgPAL5, CgCHS, CgFNS, Cg7GlcT, and Cg1,2RhaT. The G-box is a short DNA motif, the canonical binding site for bHLH transcription factors, and mutating or masking it abolished the interaction, establishing the molecular grammar of the connection.

Binding alone does not prove activation, so the team ran dual-luciferase transactivation assays, a technique in which a promoter is wired to a light-producing reporter enzyme. CgMYC2 transactivated all five promoters, with the strongest effect on CgCHS, the chalcone synthase gene that catalyzes the first committed step of flavonoid biosynthesis. As chromatin-level support, a single-sample CUT&Tag profiling experiment revealed that CgMYC2-associated genomic regions were enriched for G-box motifs across jasmonate-responsive and secondary-metabolic loci, painting a genome-wide picture of the regulator in action. Together, these assays build a causal chain from hormone perception to promoter occupancy to transcriptional output.

Genetic loss-of-function evidence sealed the argument. Using virus-induced gene silencing, a technique that co-opts a plant viral mechanism to knock down endogenous gene expression, the researchers suppressed CgMYC2 in pomelo seedlings. Naringin content dropped by roughly 21 percent, and the expression of the biosynthetic genes fell in parallel. The partial rather than complete reduction suggests redundancy among MYC-family members or contributions from other regulatory pathways, but the direction and coherence of the effect confirm that CgMYC2 is a positive, load-bearing component of the naringin regulatory network.

Perhaps the most striking result came from moving the gene into a completely different species. When the team overexpressed CgMYC2 heterologously in tomato, the transgenic plants activated their own flavonoid pathway and accumulated elevated levels of sixteen different flavonoid compounds. This cross-species functionality indicates that the MYC2-to-G-box regulatory logic is evolutionarily conserved, consistent with earlier work in tomato where an SlMYC2-SlMYB12 module orchestrates fruit flavonoid metabolism, and with jasmonate-driven MYC2 regulation of anthocyanin accumulation in Arabidopsis. A regulatory principle discovered in a medicinal pomelo thus appears to be a general design feature of plant secondary metabolism.

The practical implications extend in several directions. For breeders of Huajuhong and other citrus, CgMYC2 offers a molecular marker and a potential editing target for tuning naringin content, whether the goal is maximizing medicinal quality or reducing bitterness in juice cultivars. The study also connects to a broader agricultural context: recent work has shown that stabilizing MYC2 in citrus can confer resistance to Huanglongbing, the devastating citrus greening disease, suggesting that a single regulatory node influences both defense chemistry and quality traits. More broadly, jasmonate elicitation is already used to boost secondary metabolite production in medicinal plants, and knowing the specific transcription factor that gates a target pathway makes such elicitation strategies far more predictable and engineerable.

Scientifically, the study exemplifies how modern plant biology dissects a regulatory question by triangulating across scales: hormone physiology, gene expression kinetics, protein-protein interaction, protein-DNA binding, chromatin profiling, and transgenic functional tests all converge on the same answer. CgMYC2 emerges as a bridge between jasmonate perception and naringin biosynthesis, a single point of control where an environmental signal becomes a chemical phenotype. For a compound with documented pharmacological relevance and a central role in the identity of one of China’s most valued medicinal fruits, that bridge is likely to attract intense attention from both basic researchers and the citrus industry in the years ahead.

Subject of Research: Jasmonate-regulated transcriptional control of naringin flavonoid biosynthesis in Citrus grandis 'Tomentosa'

Article Title: CgMYC2 directly activates jasmonate-induced naringin biosynthesis in Citrus grandis 'Tomentosa'

Article References: CgMYC2 directly activates jasmonate-induced naringin biosynthesis in Citrus grandis 'Tomentosa'. (n.d.). https://doi.org/10.1007/s00299-026-03960-0

Image Credits: AI Generated

DOI: 10.1007/s00299-026-03960-0

Keywords: CgMYC2, naringin, jasmonate, Citrus grandis, flavonoid biosynthesis, bHLH transcription factor, JAZ repressor, G-box, methyl jasmonate, plant hormone signaling, secondary metabolism, virus-induced gene silencing

The team began by charting where and when VvbHLH10 switches on. Under laboratory conditions, its transcription was rapidly and strongly induced by both salt and alkali treatments, a pattern consistent with a gene recruited into the front line of the stress response. Intriguingly, the gene is also predominantly expressed in actively growing tissues, including latent buds, young stems and young tendrils, placing it at the intersection of stress defense and development. Using a VvbHLH10-GFP fusion protein, the researchers confirmed that the protein localizes to the nucleus, the expected working address for a transcription factor that binds promoter regions and orchestrates the expression of downstream target genes.

To test function rather than mere correlation, the researchers deployed two complementary experimental systems. The first was homologous overexpression in grape callus cultures, an in vitro system derived from the plant itself. When grape calli engineered to overexpress VvbHLH10 were challenged with salt and alkali stress, they survived and grew significantly better than control calli. Biochemical assays pointed to the mechanism behind that resilience: the engineered tissues accumulated markedly lower levels of reactive oxygen species (ROS) and malondialdehyde (MDA), two classic signatures of oxidative damage. Because salt and alkali stress disrupt photosynthesis and electron transport, plants typically respond with bursts of ROS that damage membranes, proteins and DNA; reducing that oxidative burden is a central goal of stress-resilience breeding.

The second system took the gene out of grapes altogether. In a heterologous expression approach, the team introduced VvbHLH10 into tomato, a widely used surrogate that allows plant scientists to ask whether a gene’s function is conserved across species. The answer was a clear yes. Transgenic tomato lines overexpressing VvbHLH10 showed markedly improved tolerance to salt-alkali treatment compared with wild-type controls, again with reduced oxidative damage and better overall growth. Cross-species validation of this kind matters for breeders because it suggests the underlying regulatory module is not a grape-specific quirk but a portable stress-protection circuit that could, in principle, be engineered into other horticultural crops facing the same soil chemistry problems.

Then came the surprise. Beyond its protective function, ectopic expression of VvbHLH10 in tomato promoted axillary bud outgrowth and altered the plants’ vegetative architecture. Axillary buds are the embryonic shoots that sit in the angle between leaf and stem, and whether they remain dormant or break out into branches is governed by a tight hormonal and transcriptional network involving strigolactones, auxin and cytokinin. A transcription factor that simultaneously modulates this developmental switch and the stress response is unusual, and it hints that VvbHLH10 belongs to a growing group of bHLH proteins whose roles have diversified beyond single functions. In practical terms, the same gene that helps a vine survive degraded soil could also be tuned to change how the plant allocates its growth, a lever for shaping canopy structure and productivity.

The dual identity of VvbHLH10 fits into a broader emerging picture of the bHLH family. With hundreds of members in most plant genomes, bHLH transcription factors have been implicated in everyone’s favorite processes, from iron uptake and flavonoid biosynthesis to light signaling and hormone crosstalk. Group 9 bHLH factors, the subclass to which VvbHLH10 belongs, have drawn particular interest for their roles in abiotic stress responses. What this study adds is evidence that in a woody perennial crop of global economic importance, one group 9 member can be rapidly mobilized by salinity and alkalinity cues, act in the nucleus to dampen oxidative injury, and at the same time remodel shoot architecture by freeing axillary buds from dormancy.

For viticulture, the implications are concrete. Salt-alkali soils are expanding in many grape-growing regions as irrigation, climate change and intensive cultivation push pH and sodium levels upward, and vineyards on marginal land often suffer stunted vines, poor bud break and yield losses. A gene that improves survival under both saline and alkaline conditions, verified in both homologous and heterologous systems, offers a candidate target for marker-assisted selection or genome editing. Because VvbHLH10 is naturally expressed in latent buds, breeders could also exploit its developmental role to improve bud fertility and branching in varieties where shy bud break limits yield. The authors position VvbHLH10 as a promising candidate for the genetic improvement of both salt-alkali tolerance and plant architecture in grapevine.

The research, led by Rui Xu and Huiping Liu as co-first authors and corresponding author Ke Li, was published open access on 12 September 2026 after acceptance on 9 September, and was supported by the Key Research and Development Project of Shandong Province, the National Natural Science Foundation of China, the Shandong Provincial Natural Science Foundation and several programs at the Shandong Academy of Agricultural Sciences. The team also released transcriptomic datasets from VvbHLH10-overexpressing tomato as supplementary material, giving the community a resource to trace which downstream pathways the transcription factor rewires, from antioxidant defenses to branching hormones.

What remains to be resolved is the direct target repertoire of VvbHLH10 and how its stress-protective and developmental outputs are mechanistically linked. If the same set of bound promoters underlies both ROS quenching and bud release, that would suggest an elegant coupling in which growth resumption under stress is actively licensed rather than merely permitted. If the two functions run through separate downstream circuits, breeders may be able to dial in salt tolerance without unwanted changes in vine shape. Either outcome broadens understanding of the functional diversification of bHLH transcription factors in horticultural crops and brings grape growers one gene closer to vines that thrive where the soil fights back.

Subject of Research: Functional characterization of the VvbHLH10 transcription factor in grapevine salt-alkali stress tolerance and axillary bud growth regulation

Article Title: VvbHLH10 promotes axillary bud growth and salt-alkali tolerance in grapevine

Article References: Xu, R., Liu, H., Mu, Q., Li, A., Wang, F., & Li, K. (2026). VvbHLH10 promotes axillary bud growth and salt-alkali tolerance in grapevine. BMC Plant Biology. https://doi.org/10.1186/s12870-026-09949-x

Image Credits: AI Generated

DOI: 10.1186/s12870-026-09949-x

Keywords: grapevine, VvbHLH10, bHLH transcription factor, salt-alkali stress, axillary bud growth, reactive oxygen species, abiotic stress tolerance, Vitis vinifera, plant architecture, viticulture, plant molecular biology, transgenic plants