Plant Physiol. pp.114.254367; First Published on February 3, 2015; doi:10.1104/pp.114.254367
From the article:
Two kiwifruit (Actinidia) species with contrasting terpene profiles were compared to understand the regulation of fruit monoterpene production. High rates of terpinolene production in ripe A. arguta fruit were correlated with increasing gene and protein expression of a terpene synthase AaTPS1 and correlated with an increase in transcript levels of the MEP pathway enzyme 1-deoxy-D-xylulose-5-phosphate synthase (DXS). In A. chinensis, AcTPS1 was identified as part of an array of eight tandemly duplicated genes and AcTPS1 expression and terpene production was observed only at low levels in developing fruit. Transient over-expression of DXS in tobacco leaves elevated monoterpene synthesis by AaTPS1 >100-fold, indicating that DXS is likely to be the key step in regulating MEP substrate flux in kiwifruit. Comparative promoter analysis identified potential NAC and EIN3-like transcription factor (TF) binding sites in the AaTPS1 promoter, and cloned members of both TF classes were able to activate the AaTPS1 promoter in transient assays. Electrophoretic mobility shift assays showed that AaNAC2, 3 and 4 bind a 28 bp fragment of the proximal NAC binding site in the AaTPS1 promoter but not the AcTPS1 promoter, where the NAC binding site was mutated. Activation could be restored by re-introducing multiple repeats of the 12 bp NAC core-binding motif. The absence of NAC transcriptional activation in ripe A. chinensis fruit can account for the low accumulation of AcTPS1 transcript, protein and monoterpene volatiles in this species. These results indicate the importance of NAC transcription factors in controlling monoterpene production and other traits in ripening fruits.