Transcription factors are the master regulators of gene expression, proteins that bind to specific DNA sequences and determine which genes are switched on and which remain silent. The bZIP family, short for basic leucine zipper, is one of the largest and most widespread transcription factor families in plants, involved in everything from seed development to stress responses. Yet despite their ubiquity, the specific role of rapeseed bZIP transcription factors in pathogen defense has remained largely unexplored. The research team, led by Pinyuan Jin and corresponding author Huajian Zhang, set out to change that by focusing on a previously uncharacterized group I bZIP factor from rapeseed, BnabZIP1, which they found to be strongly induced when rapeseed is attacked by Sclerotinia sclerotiorum.

Because rapeseed is genetically complex and difficult to manipulate, the researchers turned to a classic strategy in plant biology: heterologous expression. They introduced the rapeseed BnabZIP1 gene into Arabidopsis thaliana, the small mustard plant that serves as the workhorse model organism of plant science. This allowed the team to observe, in a genetically tractable system, exactly what BnabZIP1 does when the plant is challenged by pathogens. The results were striking. Arabidopsis lines overexpressing BnabZIP1 showed significantly enhanced resistance to Pseudomonas syringae pv. tomato DC3000, the hemibiotrophic bacterium responsible for bacterial speck disease in tomatoes and a standard model pathogen in plant immunity research.

The mechanism behind this enhanced resistance is a story of molecular subterfuge and counter-subterfuge. Pst DC3000 is famous among plant pathologists for producing a toxin called coronatine, a molecule that mimics the plant hormone jasmonic acid and tricks stomata, the tiny pores on leaf surfaces, into reopening after they have closed in response to bacterial attack. This allows the bacteria to slip inside the leaf. In the BnabZIP1 overexpression lines, the researchers observed reduced coronatine-triggered stomatal reopening, meaning the bacterial entry route was effectively sealed. At the same time, the transgenic plants deposited more callose, a sticky polysaccharide that plants use to wall off infection sites, reinforcing the physical barriers against bacterial spread.

But BnabZIP1’s influence extends far beyond stomata and callose. The researchers found that the transgenic lines were less sensitive to exogenous methyl jasmonate, a synthetic form of the jasmonic acid hormone, and accumulated lower levels of jasmonic acid after Pst DC3000 infection. This is significant because jasmonic acid and salicylic acid, another key defense hormone, often act in opposition, with salicylic acid generally promoting resistance to biotrophic pathogens and jasmonic acid promoting resistance to necrotrophs. By dampening jasmonic acid signaling, BnabZIP1 appears to tip the hormonal balance in favor of salicylic acid-mediated defenses, which are more effective against the hemibiotrophic bacterium.

The team also probed BnabZIP1’s role in pattern-triggered immunity, the plant’s first line of defense. Pattern-triggered immunity is activated when pattern recognition receptors on the plant cell surface detect pathogen-associated molecular patterns, such as flg22, a conserved 22-amino acid peptide from bacterial flagellin. In the BnabZIP1 overexpression lines, flg22 treatment triggered elevated production of reactive oxygen species, the chemical burst that plants use to kill invading microbes, and enhanced phosphorylation of mitogen-activated protein kinases, the signaling cascades that amplify immune signals inside the cell. These findings suggest that BnabZIP1 contributes to the earliest stages of immune recognition, before the pathogen has even established a foothold.

Yet the story takes an unexpected turn when the researchers shifted their focus from bacteria to fungi. When the BnabZIP1 overexpression lines were challenged with Sclerotinia sclerotiorum and Botrytis cinerea, two necrotrophic fungal pathogens that kill plant tissue and feed on the dead cells, the transgenic plants were actually more susceptible, not more resistant. This is a classic example of the trade-offs that shape plant immunity. The very hormonal and cellular changes that make BnabZIP1 lines better at fighting hemibiotrophic bacteria appear to compromise defenses against necrotrophic fungi, which thrive on the dead tissue that hemibiotroph-resistant strategies can inadvertently provide.

The findings provide new insights into the roles of rapeseed bZIP transcription factors in plant immunity and establish a foundation for future functional studies in rapeseed itself. The work was supported by the Innovation Project of Bio-breeding Laboratory of Anhui Province and the National Natural Science Foundation of China. The researchers emphasize that their results, obtained through heterologous expression in Arabidopsis, now need to be validated in rapeseed, where the genetic context is far more complex and where BnabZIP1 may interact with different partners and regulatory networks.

For a crop that feeds billions and underpins a global oilseed industry worth hundreds of billions of dollars, the identification of a single transcription factor that can modulate resistance to multiple pathogen classes is a significant step forward. If future studies can harness BnabZIP1 or its rapeseed homologs to engineer broad-spectrum disease resistance, the implications for food security could be enormous. The paradoxical nature of BnabZIP1’s effects, enhancing resistance to one pathogen class while compromising resistance to another, also serves as a reminder that plant immunity is not a simple on-off switch but a complex network of trade-offs shaped by millions of years of evolution.

As climate change and global trade continue to introduce new pathogens to new regions, the need for crops with robust, engineered disease resistance has never been greater. The discovery of BnabZIP1 adds a new piece to this puzzle, revealing how a single rapeseed transcription factor can sit at the intersection of hormonal signaling, stomatal behavior, cellular reinforcement, and immune recognition. Whether this molecular switch can be turned to the advantage of rapeseed farmers worldwide remains to be seen, but the foundation has now been laid.

Subject of Research: Plant Biology

Article Title: The rapeseed transcription factor BnabZIP1 modulates defense responses in Arabidopsis

Article References: Jin, P., Tetteh, C., Zhang, H., Wang, Y., Zhang, C., Luo, S., Zhang, T., Liu, Y., & Zhang, H. (2026). The rapeseed transcription factor BnabZIP1 modulates defense responses in Arabidopsis. BMC Plant Biology. https://doi.org/10.1186/s12870-026-09931-7

Image Credits: AI Generated

DOI: 10.1186/s12870-026-09931-7

Keywords: rapeseed, BnabZIP1, transcription factor, plant immunity, bZIP, Arabidopsis, Pst DC3000, Sclerotinia sclerotiorum, pattern-triggered immunity, jasmonic acid, transcription, factor