In January 2024, Kohji Yamada and Akira Mine published an article titled "Sugar coordinates plant defense signaling" in Science Advances, revealing the crucial role of Sugar in coordinating the defense system of the model plant Arabidopsis thaliana, and drawing a signaling flowchart of sugar in plant defense.
Plants have formed a variety of constitutive and inducible defense mechanisms to adapt to the environment during long-term biotic and abiotic stresses.
This study investigated the effects of Sucrose (Suc) on gene expression through RNA sequencing (RNA-seq), and the results showed that although both sugars act through Hexokinase (HXK), Suc is more likely to stimulate gene expression than glucose (Glc).
In this study, two non-metabolizable Glc analogs, 3-O-methyl-d-Glc and 2-deoxy-d-Glc (2DG) were applied to tomato seedlings to explore the detailed mechanism of Glc activation of defense signals. The results showed that sugar transporters and HXK contribute to 2DG-induced plant defense signaling.
Fig. 1 HXK-mediated Glc phosphorylation is required for sugar-induced defense signaling. (Yamada, et al., 2024)
Under sugar-sufficient conditions, the phosphorylation level of calcium-dependent protein kinase 5 (CPK5) is increased through Glc-6-phosphate (G6P)-mediated inhibition of protein phosphatases, thereby enhancing the defense response before plant pathogen invasion. Subsequently, recognition of bacterial flagellin activates sugar transporters leading to increased cellular G6P, which triggers CPK5-independent signaling and promotes the synthesis of the phytohormone Salicylic Acid (SA) for antimicrobial defense.
In this experiment, plants were treated with chitin under high sugar conditions (100 mM Suc) to increase the basal cellular sugar content. It was concluded that chitin-triggered SA synthesis was undetectable because sugar influx activity was not enhanced and cytoplasmic sugar content was not increased, indicating that cellular sugar content is a key factor in SA Synthesis during plant pattern-triggered immunity (PTI).
This study explains an important plant defense system that can not only inhibit pathogens but also coordinate plant defense. Based on the fact that defense signaling is energy-intensive transmission, a comprehensive view of sugar-promoted plant defense signaling is drawn, providing a new perspective for the study of plant defense mechanisms.
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