In a discovery that could reshape how gardeners and breeders protect one of the world’s most beloved flowering shrubs, researchers in China have identified a single gene that acts as a molecular guardian against the fungal pathogen responsible for devastating leaf spot disease in bigleaf hydrangea. The study, published in Plant Cell Reports, systematically mapped an entire family of regulatory genes in the hydrangea genome and then demonstrated through functional experiments that one of them, HmaERF87, serves as a positive regulator of the plant’s natural defenses.
Bigleaf hydrangea, Hydrangea macrophylla, is celebrated worldwide for its showy mophead and lacecap blooms, whose blue or pink coloration famously shifts with soil chemistry. The species is a cornerstone of the global ornamental horticulture industry and a fixture of private and public gardens alike. Yet its popularity comes with a persistent vulnerability: leaf spot disease caused by the necrotrophic fungus Corynespora cassiicola. The pathogen produces unsightly lesions that spread across foliage, diminishing the ornamental value of infected plants and imposing significant economic losses on nurseries. While chemical fungicides can suppress outbreaks, they raise environmental and cost concerns, making genetically informed breeding for resistance an increasingly attractive strategy.
To understand the molecular machinery hydrangea uses when it comes under fungal attack, the research team, led by Shuyuan Chen and Xintong Liu under the supervision of Zedong Wu and Yanming Deng, focused on the APETALA2/ethylene-responsive factor, or AP2/ERF, transcription factor family. Transcription factors are proteins that bind to specific DNA sequences and switch other genes on or off, acting as master regulators of cellular programs. The AP2/ERF superfamily is one of the largest such families in plants and is deeply implicated in how plants respond to stresses of all kinds, from drought and salinity to wounding and pathogen invasion. Its members fall into several subfamilies, defined by the presence of a highly conserved DNA-binding domain, and include the APETALA2 proteins, the ethylene-responsive factors, the dehydration-responsive element-binding proteins known as DREBs, and the related to ABI3/VP1, or RAV, proteins.
Using the recently available hydrangea genome as a reference, the researchers conducted a comprehensive genome-wide survey and identified 164 AP2/ERF genes. They classified these genes into the expected subfamilies and then painstakingly annotated their characteristics, including where each gene sits on the plant’s chromosomes, which conserved amino acid motifs the encoded proteins contain, the structural organization of the genes themselves, and the patterns of gene duplication that have shaped the family’s evolution over time. Such duplication events are a major engine of evolutionary novelty in plants, allowing duplicated genes to diverge and take on specialized functions.
Identifying the genes was only the first step. The team then asked which of these 164 candidates actually respond when the plant encounters its fungal enemy. Drawing on an existing RNA sequencing dataset generated from leaves of both resistant and susceptible hydrangea cultivars, sampled both before and after inoculation with Corynespora cassiicola, the researchers filtered the family down to 46 genes that showed a clear transcriptional response to infection. RNA sequencing measures the abundance of messenger RNA transcripts in a tissue, providing a snapshot of which genes are active at a given moment. Comparing expression between resistant and susceptible varieties, and between infected and uninfected tissue, allowed the team to pinpoint members of the family most likely to participate in the defense response.
An intriguing pattern emerged when the researchers examined the promoter regions of these infection-responsive genes. Promoters are stretches of DNA upstream of a gene that harbor cis-regulatory elements, short sequence motifs that serve as docking sites for other regulatory proteins. The analysis revealed that HmaERF genes whose expression was upregulated after fungal infection carried a higher frequency and greater copy number of jasmonate-responsive elements in their promoters. Jasmonic acid is a plant hormone central to defenses against necrotrophic fungi such as C. cassiicola, which literally feed on dead plant tissue. This enrichment suggests that the hydrangea defense program orchestrated by these transcription factors is wired, at least in part, into hormone-mediated signaling pathways, echoing a theme documented across many plant species where jasmonate and ethylene signaling jointly activate resistance to this class of pathogens.
From the pool of infection-induced candidates, three genes were selected for direct functional testing: HmaERF56, HmaERF87, and HmaERF129. To probe what these genes do, the team employed virus-induced gene silencing, or VIGS, a technique in which a modified plant virus carries a fragment of the target gene’s sequence into plant tissue. The plant’s own antiviral RNA interference machinery then recognizes the matching native transcript and degrades it, effectively knocking down the gene’s expression without generating a stable transgenic line. VIGS is particularly valuable in ornamental species such as hydrangea, which are not routinely transformed and where traditional genetics is slow. Here, the researchers applied VIGS in hydrangea leaf discs, a rapid assay platform their group had previously developed and validated in earlier work showing that ethylene plays a crucial role in leaf spot resistance.
The results were striking and specific. When HmaERF87 expression was silenced, lesions developed significantly more extensively after inoculation with C. cassiicola, indicating that the plant’s ability to contain the fungus had been compromised. Conversely, when HmaERF87 was transiently overexpressed, the area of lesions on leaf discs shrank. Together, these gain-of-function and loss-of-function results demonstrate that HmaERF87 acts as a positive regulator of leaf spot resistance: the more of it is present, the better the plant fends off the pathogen. Notably, silencing the other two candidate genes did not produce the same clear-cut effect, underscoring the value of experimental validation in distinguishing genuine defense regulators from genes whose expression changes are merely correlated with infection.
The team went on to characterize the HmaERF87 protein at the cellular level. Subcellular localization experiments confirmed that the protein accumulates in the nucleus, the expected destination for a transcription factor that must physically contact DNA to do its work. Yeast-based assays, a standard method for assessing whether a protein can activate transcription on its own, revealed that the transcriptional activation activity of HmaERF87 resides mainly in its C-terminal region. This means the tail end of the protein carries the domains responsible for recruiting the cellular machinery that initiates gene expression, while the N-terminal AP2 domain presumably handles sequence-specific DNA binding.
The broader significance of the finding extends beyond hydrangea. ERF transcription factors have been shown in numerous crops and model plants to function as regulators of immunity, with some acting as activators of defense and others as repressors. Examples include ERF5 and ERF6 in Arabidopsis, which promote jasmonate and ethylene-mediated defense against Botrytis cinerea, and ZmERF105 in maize, which bolsters resistance to another fungal pathogen. The hydrangea work adds a horticulturally important species to this growing roster and provides a concrete molecular target for breeders seeking leaf-spot-resistant cultivars, whether through marker-assisted selection that tracks favorable versions of the gene or through future gene-editing approaches.
The study also fits into a wider research program on hydrangea biology led by the same collaboration, which spans Heilongjiang University, the Jiangsu Academy of Agricultural Sciences, Northeast Agricultural University, and the Nanjing Institute of Vegetable Science. Recent work from the group has illuminated the role of abscisic acid in hydrangea responses to C. cassiicola and the family-wide analysis of other gene types in the species, including transporters that underlie the plant’s remarkable aluminum tolerance. Together, these efforts are building a systems-level picture of how this iconic ornamental copes with both biotic and abiotic challenges.
For now, the identification of HmaERF87 offers a clear lead. As a nucleus-localized, pathogen-induced transcription factor whose manipulation demonstrably alters the outcome of fungal infection, it represents one of the first functionally validated disease resistance regulators in hydrangea. Future research will need to identify the downstream defense genes that HmaERF87 controls, determine how jasmonate and other hormonal signals converge on its promoter, and test whether naturally occurring variation in this gene explains differences in resistance among hydrangea cultivars. If those threads come together, the humble molecular switch uncovered in leaf disc experiments could one day help keep hydrangea gardens full of flawless, fungus-free foliage.
Subject of Research: Identification and functional validation of the AP2/ERF transcription factor gene HmaERF87 as a positive regulator of resistance to leaf spot disease caused by Corynespora cassiicola in Hydrangea macrophylla.
Subject of Research: Agriculture
Article Title: Genome-wide AP2/ERF analysis identifies HmaERF87 as a positive regulator of Hydrangea macrophylla leaf spot resistance
Article References: Chen, S., Liu, X., Zhang, C., Zhang, Z., Chen, H., Han, Y., Chen, S., Feng, J., Wang, G., Li, C., Wu, Z., & Deng, Y. (2026). Genome-wide AP2/ERF analysis identifies HmaERF87 as a positive regulator of Hydrangea macrophylla leaf spot resistance. Plant Cell Reports, 45(9), Article 241. https://doi.org/10.1007/s00299-026-03927-1
Image Credits: AI Generated
DOI: 10.1007/s00299-026-03927-1
Keywords: Hydrangea macrophylla, Corynespora cassiicola, AP2/ERF transcription factors, HmaERF87, leaf spot resistance, virus-induced gene silencing, jasmonic acid, plant immunity, genome-wide analysis, ornamental horticulture
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Juliet Wilcox. (September 7, 2026). Study finds HmaERF87 boosts hydrangea resistance to leaf spot disease. Scienmag. https://scienmag.com/study-finds-hmaerf87-boosts-hydrangea-resistance-to-leaf-spot-disease/
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