Activity of the purified plant ABC transporter NtPDR1 is stimulated by diterpenes and sesquiterpenes involved in constitutive and induced defenses.

Within the plant ATP-binding cassette transporter family， pleiotropic drug resistance (PDR) transporters play essential functions， such as in hormone transport or defense against biotic and abiotic stresses. NtPDR1 from has been shown to be involved in the constitutive defense against pathogens through the secretion of toxic cyclic diterpenes， such as the antimicrobial substrates cembrene and sclareol from the leaf hairs (trichomes). However， direct evidence of an interaction between NtPDR1 and terpenes is lacking. Here， we stably expressed NtPDR1 in BY-2 suspension cells. NtPDR1 was purified as an active monomer glycosylated at a single site in the third external loop. NtPDR1 reconstitution in proteoliposomes stimulated its basal ATPase activity from 21 to 38 nmol of P·mg·min， and ATPase activity was further stimulated by the NtPDR1 substrates cembrene and sclareol， providing direct evidence of an interaction between NtPDR1 and its two substrates. Interestingly， NtPDR1 was also stimulated by capsidiol， a sesquiterpene produced by upon pathogen attack. We also monitored the transcriptional activity from the promoter with a reporter gene and found that， although expression was limited to trichomes under normal conditions， addition of methyl jasmonate， a biotic stress hormone， induced expression in all leaf tissues. This finding indicated that NtPDR1 is involved not only in constitutive but also in induced plant defenses. In conclusion， we provide direct evidence of an interaction between the NtPDR1 transporter and its substrates and that NtPDR1 transports compounds involved in both constitutive (diterpenes) and induced (sesquiterpenes) plant defenses.