CmCML11 interacts with CmCAMTA5 to enhance γ-aminobutyric acid (GABA) accumulation by regulating GABA shunt in fresh-cut cantaloupe

The effect of calcium chloride (CaCl2) treatment on gamma-aminobutyric acid (GABA) accumulation in fresh-cut cantaloupe and the involved mechanisms were investigated. The result showed that 1% (w/v) CaCl2 treat-ment increased GABA content and activities of glutamate decarboxylase (GAD) and succinate semialdehyde dehydrogenase (SSADH), while decreased glutamate (Glu) content and GABA transaminase (GABA-T) activities in fresh-cut cantaloupe. CmCML11 and CmCAMTA5 expressions of CaCl2-treated fruit increased by 187.4% and 165.6% than control fruit in the initial 6 h. Besides, expressions of GABA shunt genes, including CmGAD1, CmGAD2, CmGABA-T and CmSSADH were also up-regulated by CaCl2 treatment during early storage. Moreover, acting as a transcriptional activator, CmCAMTA5 could bind to the CG-box in promoters of CmGAD1, CmGABA-T and CmSSADH and activate their transcription. Furthermore, the interaction between CmCML11 and CmCAMTA5 could enhance the transcriptional activation on GABA shunt genes which were regulated by CmCAMTA5. Collectively, our findings revealed that CaCl2 treatment promoted GABA accumulation in fresh-cut cantaloupe via the combined effect of CmCML11 and CmCAMTA5 in the regulation of expressions of CmGAD1, CmGABA-T, and CmSSADH in GABA shunt.

Automated summary

This study investigated the effect of calcium chloride (CaCl2) treatment on GABA accumulation in fresh-cut cantaloupe and the underlying mechanisms. The results showed that CaCl2 treatment increased GABA content and the activities of GAD and SSADH enzymes, while reducing glutamate content and GABA-T activity. Additionally, CaCl2 treatment upregulated the expressions of CmCML11 and CmCAMTA5, as well as several GABA shunt genes, through the transcriptional activation by CmCAMTA5. Furthermore, the interaction between CmCML11 and CmCAMTA5 enhanced the transcriptional activation of GABA shunt genes. Overall, this study reveals that CaCl2 treatment promotes GABA accumulation in fresh-cut cantaloupe through the combined effect of CmCML11 and CmCAMTA5 in regulating the expressions of GABA shunt genes.