Hirschberg, Joseph , Galpaz, Navot , Kachanovsky, David , Ronin, Ira , Isaacson, Tal , Wang, Qiang .
Regulation of carotenoid biosynthesis: Lessons from mutational analysis in tomato.
Developmental regulation of transcription of carotenoid biosynthesis genes is the major mechanism that controls accumulation of pigments in flowers and fruits. To identify genes that regulate carotenoid biosynthesis we have isolated mutants in tomato (S. lycopersicum, CV M82) that affect carotenoid accumulation in flowers and fruits. Analysis of these mutants suggests that expression of carotenoid genes also responds to environmental and physiological cues. Two examples will be discussed: the mutant high-pigment 3 (hp3) and the peculiar epistasis of tangerine (t) over yellow-flesh (r). Fruits of hp3 accumulate 40% more carotenoids compared with the wild type due to a mutation in zeaxanthin epoxidase. Characterization of hp3 indicated that it is a weak ABA mutant and that increased fruit carotenoids can be attributed to pleotropic effects caused by reduced ABA levels in an organ-specific manner. The mutant yellow-flesh is impaired in phytoene synthase (Psy1) and tangerine is mutated in a carotenoid isomerase (CrtISO) that is required for the formation of all-trans lycopene. The phenotype of the double mutant tangerine/yellow-flesh indicates that tangerine is epistatic on yellow-flesh. This observation is in contrast to the general principle in biosynthetic pathways that mutations in early steps in a pathway are epistatic over later ones. It was discovered that transcription of Psy1 in the double mutant is up-regulated 100 folds as compared to yellow-flesh, thus enabling the production of enough phytoene to allow the progression of pathway. These results suggest a feedback mechanism that regulates transcription of a carotenoid gene by products of the pathway.
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1 - The Hebrew University, Genetics, Institute of Life Sciences, Jerusalem, 91904, Israel
Presentation Type: Plant Biology Abstract
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM