Characterization of the Role of PIC30 Protein in Plant Immune Response
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Plants have developed several defense mechanisms to cope with biotic and abiotic stresses, including hypersensitive response (HR), an apoptotic response of plant tissues to infecting microbes leading to systemic acquired resistance (SAR). Salicylic acid plays an important role in plants when sending signals from the sites of HR to healthy plant organs during the development of SAR. PIC30, a protein previously characterized as a transporter protein belonging to the Major Facilitator Superfamily (MFS) in the model plant Arabidopsis thaliana, transports nitrate ions and the synthetic auxin, picloram into cells. A transgenic reporter line PIC30::PIC30-GUS displayed increased expression of the fusion protein when plants were exposed to salicylic acid. When salicylic acid binds to its receptor, NPR1, copper must also bind to NPR1 to facilitate the interaction. Therefore, copper is required for the activation of defense genes during salicylic acid-mediated SAR. PIC30::PIC3-GUS transgenic line also displayed a response to salicylic acid and copper. Primary root elongation of wild-type plants was inhibited while the roots of pic30 knockout mutant displayed slight resistance to high salicylic acid and copper concentrations. Overexpression lines of pic30 displayed high inhibition suggesting a possible role of PIC30 in the transport of salicylic acid and copper ions during SAR in plants.