Abstract text: Synthesis of plant cell wall polysaccharides and glycoproteins relies on the supply of nucleotide sugars. Among them, GDP-L-fucose serves as a substrate for synthesis of xyloglucan and rhamnogalacturonan-II side chains, as well as glycoproteins. Despite its relatively low abundance, L-Fuc is necessary for proper growth and development of Arabidopsis thaliana as exemplified by the pleiotropic phenotypes of fucose-deficient mur1 mutant lacking MUR1/GMD2 - one of the two GDP-D-mannose 4,6-dehydratases (GMD) catalyzing the first reaction in the 3-step de novo synthesis of GDP-L-fucose from GDP-D-mannose. The two final reactions of this pathway are catalyzed by a bifunctional enzyme GDP-4-keto-6-deoxy-D-mannose 3,5-epimerase 4-reductase (GER) represented by two isoforms, GER1 and GER2. Here, based on the biochemical and phenotypical analysis of ger1 and ger2 mutant lines, we show that, unlike GMDs, GER1 and GER2 are functionally redundant and only simultaneous knockdown of both isoforms leads to a decrease in foliar L-Fuc content and mur1-like growth phenotype. Moreover, through analysis of ger1 ger2/GER2 plants we demonstrate that ger1 ger2 pollen is viable but infertile. Our work highlights the redundant role of GER1 and GER2 in plant development and reproduction.