Two showy traits, scent emission and pigmentation, are finely coregulated by the MYB transcription factor PH 4 in petunia flowers

Summary The mechanism underlying the emission of phenylpropanoid volatiles is poorly understood. Here, we reveal the involvement of PH 4 , a petunia MYB ‐R2R3 transcription factor previously studied for its role in vacuolar acidification, in floral volatile emission. We used the virus‐induced gene silencing (VIGS) approach to knock down PH 4 expression in petunia, measured volatile emission and internal pool sizes by GC ‐ MS , and analyzed transcript abundances of scent‐related phenylpropanoid genes in flowers. Silencing of PH 4 resulted in a marked decrease in floral phenylpropanoid volatile emission, with a concurrent increase in internal pool levels. Expression of scent‐related phenylpropanoid genes was not affected. To identify putative scent‐related targets of PH 4 , we silenced PH 5 , a tonoplast‐localized H + ‐ ATP ase that maintains vacuolar pH homeostasis. Suppression of PH 5 did not yield the reduced‐emission phenotype, suggesting that PH 4 does not operate in the context of floral scent through regulation of vacuolar pH . We conclude that PH 4 is a key floral regulator that integrates volatile production and emission processes and interconnects two essential floral traits – color and scent.