Characterization of a Major Facilitator Superfamily transporter protein in Arabidopsis
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The Major facilitator superfamily (MFS) transporter proteins regulate solute homeostasis across membranes in both prokaryotes and eukaryotes. In silico analysis suggests that the Arabidopsis genome consists of more than 120 putative genes that encode MFS transporters including PIC30. Recently we isolated several mutant alleles of Arabidopsis PIC30 genes, which were defective in nitrate and phytohormone transport. Interestingly, the Arabidopsis genome consists of a gene, PIC130H (PIC30 homologue) which shows 75.5% sequence similarity to PIC30. Furthermore, PIC30H shares similar domains such as putative MFS domain and a nodulin like domain with PIC30. Therefore, it could by hypothesized that PIC30H may function similar to PIC30. Using genetic and biochemical approaches we found that PIC30H localizes to plasma membrane similar to PIC30. Nevertheless, tissue specific expression of these two genes indicates reasonable differences in spatial expression. Arabidopsis mutants of both PIC30 (pic30) and PIC30H (pic30HKO) were resistant NO3- analog ClO3- suggesting both PIC30 and PIC30H transport NO3- inwardly. Interestingly, dark-induced hypocotyl growth of pic30HKO was hypersensitive to picloram while the hypocotyls of pic30 mutant was resistant when compared with wild type suggesting that PIC30 and PIC30H may transport picloram in an opposite direction. Taken together these results indicate that while some transport functions of PIC30 and PIC30H are similar, they may also have different transporter functions despite their sequence similarity.