Fungal Invasion Boosts Salicylic Acid and Anthocyanin Production in Apples

Jenn Hoskins
26th June, 2024

Fungal Invasion Boosts Salicylic Acid and Anthocyanin Production in Apples

Image Source: Natural Science News, 2024

Key Findings

  • Researchers at Shandong Agricultural University found that fungal infections in apples cause red circles around necrosis areas due to high anthocyanin levels
  • The study revealed that salicylic acid (SA) from fungal invasion boosts anthocyanin production in apples
  • Key genes, MdNPR1 and MdTGA2.2, were identified as crucial for SA-induced anthocyanin biosynthesis, enhancing fruit coloration
Understanding the molecular mechanisms behind plant responses to pathogens is crucial for developing better agricultural practices. One intriguing phenomenon observed in apple fruits is the appearance of a red circle surrounding necrosis areas induced by pathogens. A recent study conducted by researchers at Shandong Agricultural University has shed light on this phenomenon, revealing that the accumulation of salicylic acid (SA) due to fungal infection promotes anthocyanin biosynthesis through the MdNPR1-MdTGA2.2 module in apples[1]. The study began by inoculating apple fruits with two types of fungi, Valsa mali and Botryosphaeria dothidea. This induced the characteristic red circle around necrosis areas, similar to what is observed in the field. The researchers found that these red circles accumulated high levels of anthocyanins, which are pigments responsible for red, purple, and blue colors in plants. Importantly, the accumulation of anthocyanins was positively correlated with the levels of SA stimulated by the fungal invasion. To further understand this process, the researchers examined the role of SA in promoting anthocyanin biosynthesis. They discovered that SA enhances anthocyanin production in a dose-dependent manner in both apple calli (a type of plant tissue) and fruits. This finding aligns with earlier research showing that SA can enhance phenolic acid content in plants, including Salvia miltiorrhiza, through the action of NPR1[2]. The study then focused on MdNPR1, a key regulator in the SA signaling pathway, and its interaction with MdTGA2.2. MdNPR1 was found to positively regulate anthocyanin biosynthesis in both apple and the model plant Arabidopsis. MdNPR1 functions as a co-activator, interacting with and enhancing the activity of MdTGA2.2. This transcription factor, MdTGA2.2, binds directly to the promoters of genes involved in anthocyanin biosynthesis, thereby promoting their transcription. The importance of MdNPR1 and MdTGA2.2 was further demonstrated by genetic experiments. Suppressing the expression of either gene inhibited the coloration of apple fruits, while overexpressing them significantly enhanced fruit coloration. Additionally, silencing either MdNPR1 or MdTGA2.2 in apple fruits repressed the SA-induced fruit coloration, confirming their essential roles in this process. This study builds on previous research that highlighted the role of NPR1 in plant immunity and secondary metabolism. For instance, NPR1 is known to control systemic acquired resistance (SAR) in Arabidopsis by regulating the expression of pathogenesis-related genes, making plants more resistant to a broad spectrum of pathogens[3]. Similarly, in Salvia miltiorrhiza, NPR1 interacts with TGA transcription factors to regulate phenolic acid biosynthesis, a process that SA can modulate[2]. The current study extends these findings by demonstrating a specific role for the MdNPR1-MdTGA2.2 module in anthocyanin biosynthesis in response to fungal infection in apples. In conclusion, the research from Shandong Agricultural University provides critical insights into the molecular mechanisms underlying the red circles surrounding necrosis areas in apple fruits. By elucidating the role of the MdNPR1-MdTGA2.2 module in SA-induced anthocyanin biosynthesis, the study not only explains a previously unclear phenomenon but also offers potential avenues for enhancing fruit coloration and pathogen resistance in apple cultivation.

FruitsBiochemPlant Science

References

Main Study

1) Fungal invasion-induced accumulation of salicylic acid promotes anthocyanin biosynthesis through MdNPR1-MdTGA2.2 module in apple fruits.

Published 25th June, 2024

https://doi.org/10.1111/tpj.16890

Related Studies

2) Salicylic acid regulates phenolic acid biosynthesis via SmNPR1-SmTGA2/SmNPR4 modules in Salvia miltiorrhiza.

https://doi.org/10.1093/jxb/erad302

3) The Arabidopsis NPR1 gene that controls systemic acquired resistance encodes a novel protein containing ankyrin repeats.

Journal: Cell, Issue: Vol 88, Issue 1, Jan 1997


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