Exploring genetic redundancy of Arabidopsis thaliana Gulono-1,4 γ-lactone oxidases by transcript correlation analysis

Ascorbic acid is mainly synthesized, in plants, by the Smirnoff-Wheeler pathway; an alternative route is the L-Gulose pathway, with a last step catalyzed by Gulono-1,4 γ lactone oxidase (GULLO). The Arabidopsis thaliana Gullo gene family consists of seven isoforms AtGullo1 to 7. However, an in vivo physiological role has been attributed only to AtGullo2, which contributes to iron (Fe) loading into the developing embryos and to suberin biosynthesis in the seed coats. We applied Transcript Correlation analysis (TCA) to uncover possible functional redundancies of the AtGullo family and, possibly, to identify unique physiological roles among its isoforms. AtGullo6 is the only isoform sharing with AtGullo2 a putative direct involvement in Fe transport/deficiency responses; moreover, TCA suggests AtGullo6 involvement in the patterns of development of root cell layers and vascular tissues, relevant for solute transport including Fe. Also, TCA suggest the involvement of AtGullo1 and AtGullo4 in late flower development and early seed development: AtGullo1 in pollen tube reception/carpel or fruit development and AtGullo4 in the biosynthesis of lipid/cutin, after fertilization. Last, both AtGullo3 and AtGullo5 are involved in Casparian Strip (CS) formation/wall remodeling in roots. According to TCA, the AtGullo gene family might be therefore only partially genetically redundant, with two putative novel roles of its members: late flower development and CS formation. TCA is therefore a powerful tool to clarify functional redundancies as well as unique roles in plant gene families with members still devoid of established physiological roles.