R2R3-NaMYB8 Regulates the Accumulation of Phenylpropanoid-Polyamine Conjugates, Which Are Essential for Local and Systemic Defense against Insect Herbivores inNicotiana attenuata

Abstract

Although phenylpropanoid-polyamine conjugates (PPCs) occur ubiquitously in plants, their biological roles remain largely unexplored. The two major PPCs of Nicotiana attenuata plants, caffeoylputrescine (CP) and dicaffeoylspermidine, increase dramatically in local and systemic tissues after herbivore attack and simulations thereof. We identified NaMYB8, a homolog of NtMYBJS1, which in BY-2 cells regulates PPC biosynthesis, and silenced its expression by RNA interference in N. attenuata (ir-MYB8), to understand the ecological role(s) of PPCs. The regulatory role of NaMYB8 in PPC biosynthesis was validated by a microarray analysis, which revealed that transcripts of several key biosynthetic genes in shikimate and polyamine metabolism accumulated in a NaMYB8-dependent manner. Wild-type N. attenuata plants typically contain high levels of PPCs in their reproductive tissues; however, NaMYB8-silenced plants that completely lacked CP and dicaffeoylspermidine showed no changes in reproductive parameters of the plants. In contrast, a defensive role for PPCs was clear; both specialist (Manduca sexta) and generalist (Spodoptera littoralis) caterpillars feeding on systemically preinduced young stem leaves performed significantly better on ir-MYB8 plants lacking PPCs compared with wild-type plants expressing high levels of PPCs. Moreover, the growth of M. sexta caterpillars was significantly reduced when neonates were fed ir-MYB8 leaves sprayed with synthetic CP, corroborating the role of PPCs as direct plant defense. The spatiotemporal accumulation and function of PPCs in N. attenuata are consistent with the predictions of the optimal defense theory: plants preferentially protect their most fitnessenhancing and vulnerable parts, young tissues and reproductive organs, to maximize their fitness.

Evolutionarily Distinct BAHD N-acyltransferases are Responsible for Natural Variation of Aromatic Amine Conjugates in Rice

“…Accumulating evidence shows that PAs play an important role in plant defense responses against pathogens and insect herbivores (Newman et al, 2001;Tanaka et al, 2003;Kaur et al, 2010;Park et al, 2014). They are also suggested to play roles in sulfur starvation, heat shock, and protection against UV irradiation (Klapheck, 1983;Edreva et al, 1998;Kaur et al, 2010), although clear evidence to support these roles is yet to be reported (Fellenberg and Vogt, 2015).…”

“…PAs are a diverse group of specialized metabolites found in many plants, including wheat (Triticum aestivum), barley (Hordeum vulgare), rice (Oryza sativa), and maize (Zea mays) (Martin-Tanguy et al, 1978;Martin et al, 1985;Facchini et al, 2002;Edreva et al, 2007;Bassard et al, 2010). Accumulating evidence shows that PAs play an important role in plant defense responses against pathogens and insect herbivores (Newman et al, 2001;Tanaka et al, 2003;Kaur et al, 2010;Park et al, 2014). They are also suggested to play roles in sulfur starvation, heat shock, and protection against UV irradiation (Klapheck, 1983;Edreva et al, 1998;Kaur et al, 2010), although clear evidence to support these roles is yet to be reported (Fellenberg and Vogt, 2015).…”

Navigating natural variation in herbivory-induced secondary metabolism in coyote tobacco populations using MS/MS structural analysis

“…In the context of this study, we first used three transgenic lines produced in the U30 background and in which phenolamide metabolism is affected. When stably silencing MYB8 (irMYB8), a transcription factor that controls total phenolamide production (28,29), both N-caffeoylputrescine and unknown at m/z 347 disappeared from the extract ion current chromatograms (Fig. 5D).…”

“…S10), provided additional support that this unknown was related to putrescine-based phenolamide metabolism. N-caffeoylputrescine is a prominent defense compound in N. attenuata (29), and understanding the modulations of its metabolism has important physiological implications for the resistance strategies used by wild populations of this plant. As mentioned above, the fragment at m/z 96.055 retrieved in the idMS/MS for m/z 347 corresponded to the mass shift and likely the biochemical transformation between N-caffeoylputrescine and the unknown at m/z 347.196.…”

“…N. attenuata populations represent a primary food source for insects that colonize the ecosystem after fires, and a vast array of genes and dependent metabolic pathways underlying resistance traits to native herbivores have been functionally characterized in this species. Among the major compound classes that contribute to the antiherbivore defense mechanisms of this plant is nicotine, a neurotoxin that functions synergistically with antidigestive plant proteins (26,27), phenolic derivatives that exhibit strong tissuespecific responses to insect herbivory (28,29), and 17-hydroxygeranyllinalool diterpene glycosides (HGL-DTGs) (30).…”