CmTGA8-CmAPX1/CmGSTU25 regulatory model involved in trehalose induced cold tolerance in oriental melon seedlings.

Plants have developed complex regulatory networks to adapt to various stresses, including cold stress. Trehalose (Tre), known as the "sugar of life," plays a crucial role in enhancing cold tolerance by triggering antioxidation. However, the underlying regulatory mechanisms remain unclear. This study examines the transcription factor gene CmTGA8, which is induced by Tre under normal and cold conditions in melon seedlings (Cucumis melo L.), through transcriptome analysis and RT-qPCR. Reverse genetic analyses showed that silencing CmTGA8 reduced ascorbate peroxidase (APX) and glutathione S-transferase (GST) activities, suppressed CmAPX1 and CmGSTU25 expression, and increased cold susceptibility in melon seedlings. Our previous reports illustrated that Tre treatment significantly induced the expression of respiratory burst oxidase homologues (CmRBOHD) gene, encoding NADPH oxidases responsible for generating apoplastic HO. Silencing CmRBOHD markedly inhibited CmTGA8, CmAPX1, and CmGSTU25 expression and reduced cold tolerance. Moreover, HO treatment upregulated CmTGA8 expression, while the NADPH oxidase inhibitor diphenyleneiodonium (DPI) treatment downregulated it. Additionally, CmTGA8 physically interacted with CmAPX1 and CmGSTU25 to promote their expression. Silencing CmGSTU25 decreased GST activity and ferric reducing ability of plasma (FRAP), further increasing cold sensitivity. These findings identify a novel regulatory hierarchy of the HO-CmTGA8-CmAPX1/CmGSTU25 cascade in the Tre-mediated cold response pathway in melon seedlings.