Biotic Stress Hormone Research Articles

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 Nicotiana tabacum 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 N. tabacum 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 Pi·mg-1·min-1, 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 N. tabacum upon pathogen attack. We also monitored the transcriptional activity from the NtPDR1 promoter in situ with a reporter gene and found that, although NtPDR1 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.

Multiple hormone treatment revealed novel cooperative relationships between abscisic acid and biotic stress hormones in cultured cells

Phytohormones have vigorous crosstalk relationships. For example, abscisic acid (ABA), a hormone involved in abiotic stress responses, has antagonistic interactions with plant hormones that play pivotal roles in defense responses, including salicylic acid (SA) and methyl-jasmonic acid (MeJA). Evidence indicates that the relationships among these plant hormones extend beyond simple antagonism. To explore the interplay between hormones in detail, we analyzed the effects of double hormone treatment on gene expression. By contrast to the antagonistic effects reported previously, our data indicates that ABA interacts with SA and MeJA cooperatively as well. Particularly many genes responded only to double hormone treatment, and, interestingly, the loci that responded to ABA+SA also responded to ABA+MeJA. The expression of early-response genes following double hormone treatment did not fit the linear superposition of individual hormone treatments, in contrast to mammalian and prokaryotic cell responses to multiple chemical stimuli. Thus, synergies in these plant hormone signalings are not simply the sum of individual responses. ABA and SA collaboratively down-regulated the expression of genes involved in cell cycle progression at G2/M phase. Presumably, plants interpret combined hormone signals differently from individual signals in order to respond appropriately to their environmental conditions.