Examining the Role of Arabinogalactan-Proteins in Agrobacterium-mediated Transformation of Citrus, Poster Board #132

A possible role of arabinogalactan proteins (AGPs) in control of shoot regeneration and cell transformability in stem explants of two Citrus cultivars, 'Carrizo' citrange (Citrus sinensis L. x Poncirus trifoliata L.) and ‘Duncan’ grapefruit (Citrus paradisi) was investigated. The regeneration potential (RP) of both 'Carrizo' citrange and ‘Duncan’ grapefruit was suppressed by the treatment of explants with the βGlcY reagent (a dye with high specificity for binding to AGPs). In the case of 'Carrizo', decreased RP of βGlcY-treated explants was the result of both lower number of shoots on the explants that had shoots and decreased percentage of explants with shoots.  For ‘Duncan’, treatment with βGlcY reduced RP only by lowering the percentage of explants with shoots but it did not affect number of shoots on the explants with shoots. Treatment of Citrus explants with αManY reagent, which does not bind AGPs, did not affect their ability to regenerate shoots significantly. The amounts of AGPs measured in stems were comparable for both cultivars. Exposure of dark-grown seedlings for 7 days to white light resulted in a 50% increase in tissue concentration of AGPs.  White light treatment of plants also resulted in higher RPs in explants obtained from those plants compared to etiolated explants. Cell transformability of white light-irradiated explants of both cultivars was higher when compared to etiolated explants.  Our data suggest that AGPs play important role in processes controlling differentiation and genetic transformation of Citrus cells by Agrobacterium.