Title

Investigating the role of carotenoid cleavage dioxygenase 4 in Mimulus lewisii nectar guide pigmentation

Date of Completion

Spring 5-1-2017

Thesis Advisor(s)

Yaowu Yuan; Arlene Albert

Honors Major

Molecular and Cell Biology

Disciplines

Biodiversity | Developmental Biology | Evolution | Genetics | Molecular Biology | Molecular Genetics

Abstract

Variation in the carotenoid biosynthetic pathway (CPB) in flowers is evolutionarily important due to its influence on pollinator specificity. In tomato flowers,elimination of β-carotenoid hydroxylase (BCH1) lead to an expected change in carotenoid composition, but an unexpected decrease in concentration by ~80% (Galpaz et al, 2006). Carotenoid cleavage dioxygenase 4 (CCD4) is an enzyme known to cleave carotenoids into colorless apocarotenoids. We hypothesized that CCD4 may be responsible for the observed decrease in carotenoidconcentration by selectively degrading carotenes (i.e. β-carotene) more than xanthophylls (i.e. zeaxanthin). To investigate this process in Mimulus lewisii, we developed RNAi lines for two CBP structural genes (BCH1 and ZEP1), then crossed them with a CCD4-RNAi line. Relative to the wild type, BCH1knockdown causes partial β-carotene accumulation, but a 90% decrease in total carotenoid concentration. ZEP1 knockdown causes partial zeaxanthin accumulation, but an 86% decrease in carotenoid concentration. CCD4knockdown causes a 50% increase in total carotenoid concentration, without affecting composition. Although concentration is partially restored by simultaneous knockdown of CCD4 with BCH1 or ZEP1, our data indicate thatCCD4 degrades all carotenoids non-selectively. Therefore, we suggest thatCCD4 is not responsible for the previously observed phenomenon and that differential storage capacity for carotenoids is the most likely explanation.

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