Circadian Regulation of the PhCCD1 Carotenoid Cleavage Dioxygenase Controls Emission of [beta]-Ionone, a Fragrance Volatile of Petunia Flowers1

• Published in: Plant physiology (Bethesda) Vol. 136; no. 3; p. 3504
• Main Authors: Simkin, Andrew J, Underwood, Beverly A, Auldridge, Michele, Loucas, Holly M
• Format: Journal Article
• Language: English
• Published: Rockville American Society of Plant Biologists 01.11.2004
• Subjects: Carotenoids; Circadian rhythms; Emissions control; Flowers; Leaves; Tomatoes; Transgenic plants
• ISSN: 0032-0889; 1532-2548

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.