The Citrus CitERF6 contributes to citric acid degradation via up-regulation of CitAclα1, encoding ATP-citrate lyase subunit α.

Citric acid is the most abundant organic acid in citrus fruit, and the acetyl-CoA pathway potentially plays an important role in citric acid degradation, which occurs during fruit ripening. Analysis of transcripts during fruit development of key genes in the acetyl-CoA pathway and transient overexpression assay in citrus leaves indicated that CitAcl alpha 1 could be a potential target gene involved in citrate degradation. In order to understand more about CitAcl alpha 1, 23 transcription factors coexpressed with CitAcl alpha 1 in citrus fruit were identified by RNA-seq. Using dual-luciferase assays, CitERF6 was shown to trans-activate the promoter of CitAcl alpha 1 and electrophoretic mobility shift assays (EMSAs) showed that CitERF6 directly bound to a 5'-CAACA-3' motif in the CitAcl alpha 1 promoter. Furthermore, citric acid content was significantly reduced when CitERF6 was overexpressed in transgenic tobacco leaves. Taken together, these results indicate an important role for CitERF6 in transcriptional regulation of CitAcl alpha 1 and control of citrate degradation.