The Arabidopsis thaliana Gulono-1,4 γ-lactone oxidase 2 (GULLO2) facilitates iron transport from endosperm into developing embryos and affects seed coat suberization.

Plants synthesize ascorbate (ASC) via the D-mannose/L-galactose pathway whereas animals produce ASC and HOvia the UDP-glucose pathway, with Gulono-1,4 γ-lactone oxidases (GULLO) as the last step. A. thaliana has seven isoforms, GULLO1-7; previous in silico analysis suggested that GULLO2, mostly expressed in developing seeds, might be involved in iron (Fe) nutrition. We isolated atgullo2-1 and atgullo2-2 mutants, quantified ASC and HO in developing siliques, Fe(III) reduction in immature embryos and seed coats. Surfaces of mature seed coats were analysed via atomic force and electron microscopies; suberin monomer and elemental compositions of mature seeds, including Fe, were profiled via chromatography and inductively coupled plasma-mass spectrometry. Lower levels of ASC and HO in atgullo2 immature siliques are accompanied by an impaired Fe(III) reduction in seed coats and lower Fe content in embryos and seeds; atgullo2 seeds displayed reduced permeability and higher levels of C18:2 and C18:3 ω-hydroxyacids, the two predominant suberin monomers in A. thaliana seeds. We propose that GULLO2 contributes to ASC synthesis, for Fe(III) reduction into Fe(II). This step is critical for Fe transport from endosperm into developing embryos. We also show that alterations in GULLO2 activity affect suberin biosynthesis and accumulation in the seed coat.