NRT/PTR transporters are essential for translocation of glucosinolate defence compounds to seeds

Two high-affinity proton-dependent transporters of glucosinolates have been identified in Arabidopsis and termed GTR1 and GTR2; these transporters are essential for transporting glucosinolates to seeds, offering a means to control the allocation of defence compounds in a tissue-specific manner, which may have agricultural biotechnology implications. Glucosinolates are important plant defence compounds. They are synthesized in various tissues and then translocated to the seeds, where they accumulate. In this study, Barbara Halkier and colleagues examine the molecular basis of this long-distance transport process. They identify two high-affinity, proton-dependent glucosinolate-specific transporters in Arabidopsis, termed GTR1 and GTR2. These transporters control the loading of glucosinolates from the apoplast into the phloem. The authors' specific and complete elimination of glucosinolates from Arabidopsis seeds, combined with the compounds' retention in vegetative tissues, establishes transport engineering as a potential approach for eliminating anti-nutritional natural products in high-value crops. In plants, transport processes are important for the reallocation of defence compounds to protect tissues of high value1, as demonstrated in the plant model Arabidopsis, in which the major defence compounds, glucosinolates2, are translocated to seeds on maturation3. The molecular basis for long-distance transport of glucosinolates and other defence compounds, however, remains unknown. Here we identify and characterize two members of the nitrate/peptide transporter family, GTR1 and GTR2, as high-affinity, proton-dependent glucosinolate-specific transporters. The gtr1 gtr2 double mutant did not accumulate glucosinolates in seeds and had more than tenfold over-accumulation in source tissues such as leaves and silique walls, indicating that both plasma membrane-localized transporters are essential for long-distance transport of glucosinolates. We propose that GTR1 and GTR2 control the loading of glucosinolates from the apoplasm into the phloem. Identification of the glucosinolate transporters has agricultural potential as a means to control allocation of defence compounds in a tissue-specific manner.