Overexpression of CsANR Increased Flavan-3-ols and Decreased Anthocyanins in Transgenic Tobacco

Abstract

Anthocyanins and flavan-3-ols are distributed widely in plants and synthesized by a common biosynthetic pathway. Anthocyanin reductase (ANR) represents branching-point enzyme of this pathway converting anthocyanidins to flavan-3-ols. Since tea contains highest amount of flavonoids, a cDNA encoding anthocyanin reductase from tea (CsANR) was overexpressed in transgenic tobacco to check the influence on anthocyanin and flavan-3-ols. The transgenic tobacco was confirmed by genomic PCR and expression of transgene was analyzed through semiquantitative PCR. Interestingly flowers of transgenic tobacco were light pink/white in color instead of dark pink in wild tobacco, documenting the decrease in anthocyanins content. Upon measurement, flower anthocyanin content was found to be lesser. While flavan-3-ols (epicatechin and epigallocatechin) contents were increased in leaf tissue of transgenic lines. The expressions of other endogenous flavonoid biosynthetic pathway genes in different floral parts (sepal, petal, stamen, and carpel) of CsANR overexpressing tobacco as well as wild tobacco were analyzed. The transcript levels of PAL and CHI genes were downregulated, while transcript levels of F3H, FLS, CHS, ANR1, and ANR2 genes were upregulated in all floral parts of CsANR transgenic plants compared to wild tobacco. The expressions of DFR and ANS genes were also spatially modulated in different floral parts due to overexpression of CsANR. Thus, CsANR overexpression increased flavan-3-ols and decreased anthocyanin content by modulating the expressions of various flavonoid biosynthetic pathway genes in flower of tobacco. These changes might be responsible for the observed pollen tube in the pollens of CsANR overexpressing transgenic tobacco when they were still in the anther before pollination.