The secret of mycorrhizal symbiosis to improve the salt resistance of sour dates has been cracked

Secondary salinization of soil in winter jujube orchards in the Yellow River beach.

Adaptation mechanism of mycorrhizal jujube trees under salt stress. Images are provided by the author of the paper

Under adversity conditions, plants often recruit microorganisms at the rhizosphere to improve their ability to adapt. Arbuscular mycorrhizal fungi are such soil microorganisms, and their symbiosis with the root system promotes plant growth and development.

Jujube tree is an important economic forest tree species native to China, with a cultivated area of 2 million hectares. Currently, drought and soil salinization are the main adversity limiting factors for jujube production in the main producing areas. Studies have shown that the salt tolerance of plants is closely related to the ability of plants to maintain homeostasis of potassium and sodium ions.

Sour dates are wild species of jujube trees and are widely used as rootstocks in jujube cultivation. However, the scientific question of how symbiosis between fungi and roots function at the physiological and molecular levels in the growth of jujube trees has remained unanswered.

Recently, Huang Jian, an associate researcher at Northwest A & F University, led a research team to uncover the secret of this biological phenomenon.

Huang Jian’s research group found in the study of jujube trees that mycorrhizal symbiosis has a promoting effect on the absorption and transport of sodium ions, but has a stronger effect on the accumulation of potassium ions in leaves. By comparing transcriptome analysis and yeast function complementarity studies, the research group found that mycorrhizal symbiosis induced the expression of ZjHAH7 gene to initiate the excretion of hydrogen ions, and improving the absorption and transport of potassium ions by dates was the main way to maintain the homeostasis of potassium and sodium ions in leaves.

Huang Jian: Previous studies have shown that in the reciprocal symbiosis relationship of mycorrhizal, host plants are mainly provided to symbiotic fungi in the form of fatty acids as the main carbon source, and converted into triglycerides for storage in mycorrhizal fungal cells.

Huang Jian’s research group found in this study that mycorrhizal symbiosis not only increased the fatty acid content of the root system of sour dates, but also simultaneously increased the fatty acid content of leaves, especially palmitic acid, oleic acid, trans oleic acid and linoleic acid.

“The research group further confirmed that mycorrhizal symbiosis increasing the fatty acid content in leaves is also a conservative symbiophysiological effect by determining the fat of mycorrhizal poplar and alfalfa plants.” Huang Jian further added.

Their findings were published in the recently published Plant Physiology. The paper elucidated the analysis of the expression patterns of genes related to fatty acid synthesis pathways by the research group, and found that there were differences in the regulatory mechanism of mycorrhizal symbiosis on the biosynthesis and accumulation of fatty acids in the roots and leaves, and although mycorrhizal symbiosis increased the content of triglycerides in the roots, the triglycerides in the leaves did not increase; through the analysis of genes related to the triglyceride synthesis pathway, it was found that only the ZjDGAT2 gene in the roots was upregulated after mycorrhizal symbiosis, and there was no obvious regulatory effect in the leaves. Studies have further shown that the increase in triglycerides in jujube root mainly comes from the storage and utilization of mycorrhizal fungi, while the fatty acid content in the leaves is significantly increased, but not stored in the form of triglycerides.

Experts in related fields believe that this study provides a comprehensive understanding of mycorrhizal symbiosis to improve the adaptability of woody plants to salt stress, elucidates the mechanism of mycorrhizal symbiosis to improve the ion homeostasis of host plants, and discovers the new effect of mycorrhizal symbiosis in regulating the metabolism of fatty acids in host plants.

Doctoral student Ma Zhibo is the first author of the paper, and Associate Researcher Huang Jian is the corresponding author. The research was funded by the National Natural Science Foundation of China, the Key Open Project of the Tarim Basin Biological Resources Conservation and Utilization Laboratory of the Xinjiang Production and Construction Corps, and the Tang Zhongying Foundation. (Source: China Science Daily, Jin Jun, Zhang Xingyong)

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