How Soil Fungi Partnership Changes Gene Activity in Walnut Tree Roots

Greg Howard
28th May, 2024

How Soil Fungi Partnership Changes Gene Activity in Walnut Tree Roots

Image Source: Natural Science News, 2024

Key Findings

  • The study analyzed how the English walnut (Juglans regia) rootstock responds to colonization by the arbuscular mycorrhizal fungus Rhizophagus irregularis
  • Mycorrhizal walnut trees showed significant increases in growth and higher nitrogen and phosphorus levels in both roots and shoots compared to non-colonized plants
  • Researchers identified 1,549 genes that were differentially expressed in mycorrhizal walnut roots, with 832 genes up-regulated and 717 down-regulated
Walnut trees are cultivated globally for their valuable timber and nut production. These trees are often heterografted, meaning they combine different plant parts to optimize growth conditions, anchorage, vigor, and resistance to soil-borne pests and diseases. However, no single rootstock can tolerate all the factors affecting walnut production. In Europe, Juglans regia, also known as the English walnut, is commonly used as a rootstock. Like most terrestrial plants, walnut trees form arbuscular mycorrhizal (AM) symbioses, which enhance water and nutrient uptake and provide additional ecosystem benefits. Despite the widespread use of AM symbiosis, its effects on root gene regulation in walnut trees had not been previously assessed. A recent study conducted by INRAE, Institut Agro, and Univ. Bourgogne Franche-Comté aimed to fill this gap by analyzing the response of a J. regia rootstock to colonization by the arbuscular mycorrhizal fungus Rhizophagus irregularis DAOM197198[1]. The study found significant increases in plant growth and nitrogen and phosphorus concentrations in both roots and shoots of mycorrhizal plants compared to non-colonized plants. Additionally, the researchers identified 1,549 genes that were differentially expressed, with 832 up-regulated and 717 down-regulated. This study builds on previous research highlighting the benefits of AM symbiosis. For instance, it has been established that AM associations provide nutritional benefits, particularly in terms of inorganic phosphate (Pi), leading to improved plant growth and defense responses[2]. The current study corroborates these findings by demonstrating enhanced nutrient uptake and growth in mycorrhizal walnut trees. Moreover, the study revealed that some rootstock genes involved in plant nutrition through the mycorrhizal pathway are regulated similarly to those in other mycorrhizal woody species like Vitis vinifera (grapevine) and Populus trichocarpa (poplar). This suggests a conserved mechanism across different plant species for optimizing nutrient uptake through AM symbiosis. The research also performed an enrichment analysis on Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, uncovering some regulations specific to J. regia, such as the juglone pathway. Juglone is a compound produced by walnut trees that can inhibit the growth of other plants, a phenomenon known as allelopathy. Understanding how AM symbiosis affects the juglone pathway could provide insights into managing walnut orchards more effectively. Previous studies have shown that AM symbiosis induces various transcriptional and metabolic changes in plants. For example, in Medicago truncatula, mycorrhization was found to up-regulate genes involved in flavonoid, terpenoid, jasmonic acid (JA), and abscisic acid (ABA) biosynthesis[2]. These biochemical pathways are crucial for plant defense and stress responses. The current study extends this understanding by showing specific gene regulation in walnut rootstocks, highlighting the complex interplay between AM symbiosis and plant metabolism. Another relevant aspect is the role of lipids in AM symbiosis. During this symbiotic relationship, significant amounts of lipids are generated, modified, and transported within the root cells to accommodate the fungus. Specific lipid biosynthetic enzymes and transporters are required for this process[3]. The current study did not focus on lipid biosynthesis but contributes to the broader understanding of how AM symbiosis affects various metabolic pathways in plants. In summary, this study by INRAE, Institut Agro, and Univ. Bourgogne Franche-Comté underscores the importance of AM symbiosis in enhancing nutrient uptake and growth in walnut trees. It also reveals specific gene regulations in J. regia that could inform future research and breeding programs aimed at improving walnut cultivation. By integrating these findings with previous research, we gain a more comprehensive understanding of the multifaceted benefits of AM symbiosis in plants.

BiochemPlant ScienceMycology

References

Main Study

1) Arbuscular mycorrhizal symbiosis with Rhizophagus irregularis DAOM197198 modifies the root transcriptome of walnut trees.

Published 27th May, 2024

https://doi.org/10.1007/s00572-024-01152-w

Related Studies

2) Enhanced Secondary- and Hormone Metabolism in Leaves of Arbuscular Mycorrhizal Medicago truncatula.

https://doi.org/10.1104/pp.16.01509

3) Arbuscular mycorrhiza-specific enzymes FatM and RAM2 fine-tune lipid biosynthesis to promote development of arbuscular mycorrhiza.

https://doi.org/10.1111/nph.14533


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