Carotenoids are thought to be the precursors of terpenoid volatile compounds that contribute to flavor and aroma. One such volatile, beta-ionone, is important to fragrance in many flowers, including petunia (Petunia hybrida). However, little is known about the factors regulating its synthesis in vivo. The petunia genome contains a gene encoding a 9,10(9',10') carotenoid cleavage dioxygenase, PhCCD1. The PhCCD1 is 94% identical to LeCCD1A, an enzyme responsible for formation of beta-ionone in tomato (Lycopersicon esculentum; Simkin AJ, Schwartz SH, Auldridge M, Taylor MG, Klee HJ [2004] Plant J [in press]). Reduction of PhCCD1 transcript levels in transgenic plants led to a 58% to 76% decrease in beta-ionone synthesis in the corollas of selected petunia lines, indicating a significant role for this enzyme in volatile synthesis. Quantitative reverse transcription-PCR analysis revealed that PhCCD1 is highly expressed in corollas and leaves, where it constitutes approximately 0.04% and 0.02% of total RNA, respectively. PhCCD1 is light-inducible and exhibits a circadian rhythm in both leaves and flowers. beta-Ionone emission by flowers occurred principally during daylight hours, paralleling PhCCD1 expression in corollas. The results indicate that PhCCD1 activity and beta-ionone emission are likely regulated at the level of transcript.
Simkin, Andrew J. Underwood, Beverly A. Auldridge, Michele. Loucas, Holly M. Shibuya, Kenichi. Schmelz, Eric. Clark, David G. Klee, Harry J.
Plant physiology.
2004.
136(3).
3504-14.