Fruit aroma plays a critical role in consumer appeal and market value, with esters being key contributors to the signature fragrance of apples. Although the lipoxygenase (LOX) pathway is known to drive the biosynthesis of aroma volatiles, the transcriptional regulators that modulate this pathway remain largely unknown. Recent research has identified transcription factors involved in terpene or ester production in various fruits, yet few studies have explored how stress-responsive genes affect aroma biosynthesis. Moderate abiotic stress, such as salinity, has shown potential in enhancing flavor-related metabolites in fruits. Based on these challenges, further investigation is needed into the stress-mediated regulation of aroma-related genes to improve fruit flavor and resilience.
Researchers from Shandong Agricultural University and the Shandong Institute of Pomology have published (DOI: 10.1093/hr/uhae215) a study in Horticulture Research (August 8, 2024), unveiling how the gene MdASG1 enhances apple aroma under salt stress. The team identified MdASG1 as a direct activator of MdLOX1a, a key gene in the LOX pathway that drives ester biosynthesis. Their findings show that MdASG1 upregulates aroma compound production and improves stress tolerance in apple and tomato plants, providing a promising genetic target for breeding flavorful, stress-resilient fruit.
The researchers first confirmed that MdLOX1a is highly expressed during apple ripening and correlates positively with ester content. Using yeast one-hybrid screening, they identified MdASG1 as a transcription factor that directly binds to the MdLOX1a promoter. EMSA and dual-luciferase assays confirmed that MdASG1 activates MdLOX1a expression. Transient overexpression of MdASG1 in apple fruit significantly increased the levels of key volatiles like 1-hexanol and hexyl acetate, while silencing the gene suppressed these compounds. Stable overexpression in apple calli and tomato plants further validated the role of MdASG1 in boosting aroma production. Under salt stress, MdASG1-overexpressing plants exhibited greater tolerance, higher expression of LOX pathway genes, and elevated aroma volatiles. In contrast, CRISPR/Cas9-mediated knockout of MdASG1 resulted in reduced volatile levels and no response to salt stress. These findings reveal that MdASG1 mediates aroma biosynthesis through stress-responsive regulatory pathways, functioning both as a flavor enhancer and a stress-response factor.
“Our study uncovers a novel function of MdASG1, linking abiotic stress response with aroma biosynthesis in apples,” said Prof. Xuesen Chen, senior author of the study. “By activating MdLOX1a, MdASG1 significantly improves aroma compound production, especially under moderate salt stress. This opens new possibilities for breeding flavorful and resilient fruit crops suited for suboptimal environments.”
This discovery presents a dual opportunity: enhancing fruit quality while adapting crops to increasingly saline soils. As global agricultural land faces challenges from salinization, using genes like MdASG1 to improve flavor and stress resilience could help maintain both crop yield and marketability. Furthermore, this regulatory mechanism may extend beyond apples to other horticultural crops, as demonstrated by similar effects in tomato. Future breeding and biotechnological strategies could leverage MdASG1 to meet growing consumer demands for tastier fruit, even under environmental stress.
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References
DOI
10.1093/hr/uhae215
Original Source URL
https://doi.org/10.1093/hr/uhae215
Funding information
We thank the National Natural Science Foundation of China (grant nos. 31701892, 32002047, and 32172533), the Natural Science Foundation of Shandong Province (grant no. ZR2022MC017), and the Agricultural Variety Improvement Project of Shandong Province (grant no. 2022LZGC010).
About Horticulture Research
Horticulture Research is an open access journal of Nanjing Agricultural University and ranked number one in the Horticulture category of the Journal Citation Reports ™ from Clarivate, 2023. The journal is committed to publishing original research articles, reviews, perspectives, comments, correspondence articles and letters to the editor related to all major horticultural plants and disciplines, including biotechnology, breeding, cellular and molecular biology, evolution, genetics, inter-species interactions, physiology, and the origination and domestication of crops.