Extracellular Vesicle GABA Responds to Cadmium Stress, and GAD Overexpression Alleviates Cadmium Damage in Duckweed

Zhanpeng Sun ^1,2 Ziyang Qu ^1,3 Yuman He ⁴ Yun Xing ^1,3 Sizheng Liu ^1,3 Yi Hu ^1,3 Yumeng Jiang ^1,3 Yiqi Yu ^1,3 Yuanyuan Liu ^1,3 Weibo Sun ^1,3 Lin Yang ^1,3*

• ¹ Key Laboratory of Animal and Plant Resistance, College of Life Sciences, Tianjin Normal University, Tianjin, China
• ² Faculty of Education, Tianjin Normal University, Tianjin, China
• ³ Tianjin Normal University, Tianjin, China
• ⁴ School of Life Sciences, Westlake University, Hangzhou, Zhejiang, China

Cadmium (Cd) pollution lead to ecological problems and cause severe damages to plants.Investigating the signal response to Cd is crucial for improving Cd resistance during phytoremediation. Recent studies have shown that γ-aminobutyric acid (GABA) accumulates rapidly in response to environmental stress. However, the real-time changes in GABA signaling activity have not been directly measured by biosensors, and the mechanistic link between GABA metabolism and stress adaptation remains unclear. In the study herein, a sensitive GABA sensor iGABASnFR was transferred into plant firstly. The glutamate-decarboxylase (GAD), a key enzyme that promotes the conversion of Glu to GABA, was over-expressed in duckweed. The results showed that: (1) GABA in extracellular vesicles of duckweed responded under Cd stress, which was observed by iGABASnFR transgeic duckweed. The GABA content in extracellular vesicles was also enhanced during Cd treatment; (2) GAD over-expressing transgenic duckweed showed an improved photosynthesis ability and antioxidant system during Cd stress; (3) the Cd accumulation was increased in GAD transgenic duckweed showed by Cd 2+ flow, Cd content and Cd staining in protoplasts by flowsight. This study provides new insights into the responds of GABA in extracellular vesicles during Cd stress, and provides evidence that the GABA metabolism enzyme GAD enhances Cd stress resistance and Cd accumulation.