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Recombinant yeast as a functional tool for understanding bitterness and cucurbitacin biosynthesis in watermelon ( Citrullus spp.)
Author(s) -
DavidovichRikanati Rachel,
Shalev Lior,
Baranes Nadine,
Meir Ayala,
Itkin Maxim,
Cohen Shahar,
Zimbler Kobi,
Portnoy Vitaly,
Ebizuka Yutaka,
Shibuya Masaaki,
Burger Yosef,
Katzir Nurit,
Schaffer Arthur A.,
Lewinsohn Efraim,
Tadmor Ya'akov
Publication year - 2015
Publication title -
yeast
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.923
H-Index - 102
eISSN - 1097-0061
pISSN - 0749-503X
DOI - 10.1002/yea.3049
Subject(s) - citrullus lanatus , biology , yeast , gene , biochemistry , atp synthase , triterpene , botany , medicine , alternative medicine , pathology
Cucurbitacins are a group of bitter‐tasting oxygenated tetracyclic triterpenes that are produced in the family Cucurbitaceae and other plant families. The natural roles of cucurbitacins in plants are probably related to defence against pathogens and pests. Cucurbitadienol, a triterpene synthesized from oxidosqualene, is the first committed precursor to cucurbitacins produced by a specialized oxidosqualene cyclase termed cucurbitadienol synthase. We explored cucurbitacin accumulation in watermelon in relation to bitterness. Our findings show that cucurbitacins are accumulated in bitter‐tasting watermelon, Citrullus lanatus var. citroides , as well as in their wild ancestor, C. colocynthis , but not in non‐bitter commercial cultivars of sweet watermelon ( C. lanatus var. lanatus ). Molecular analysis of genes expressed in the roots of several watermelon accessions led to the isolation of three sequences ( Cc CDS1, Cc CDS2 and Cl CDS1), all displaying high similarity to the pumpkin CpCPQ , encoding a protein previously shown to possess cucurbitadienol synthase activity. We utilized the Saccharomyces cerevisiae strain BY4743, heterozygous for lanosterol synthase, to probe for possible encoded cucurbitadienol synthase activity of the expressed watermelon sequences. Functional expression of the two sequences isolated from C. colocynthis ( CcCDS 1 and CcCDS2 ) in yeast revealed that only Cc CDS2 possessed cucurbitadienol synthase activity, while CcCDS1 did not display cucurbitadienol synthase activity in recombinant yeast. ClCDS1 isolated from C. lanatus var. lanatus is almost identical to CcCDS1 . Our results imply that CcCDS2 plays a role in imparting bitterness to watermelon. Yeast has been an excellent diagnostic tool to determine the first committed step of cucurbitacin biosynthesis in watermelon. Copyright © 2014 John Wiley & Sons, Ltd.