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.

Constrained to develop within the seed, the plant embryo must adapt its shape and size to fit the space available. Here, we demonstrate how this adjustment shapes metabolism of photosynthetic embryo. Noninvasive NMR-based imaging of the developing oilseed rape (Brassica napus) seed illustrates that, following embryo bending, gradients in lipid concentration became established. These were correlated with the local photosynthetic electron transport rate and the accumulation of storage products. Experimentally induced changes in embryo morphology and/or light supply altered these gradients and were accompanied by alterations in both proteome and metabolome. Tissue-specific metabolic models predicted that the outer cotyledon and hypocotyl/radicle generate the bulk of plastidic reductant/ATP via photosynthesis, while the inner cotyledon, being enclosed by the outer cotyledon, is forced to grow essentially heterotrophically. Under field-relevant highlight conditions, major contribution of the ribulose-1,5-bisphosphate carboxylase/oxygenase-bypass to seed storage metabolism is predicted for the outer cotyledon and the hypocotyl/radicle only. Differences between in vitro-versus in planta-grown embryos suggest that metabolic heterogeneity of embryo is not observable by in vitro approaches. We conclude that in vivo metabolic fluxes are locally regulated and connected to seed architecture, driving the embryo toward an efficient use of available light and space.

Summary• Herbivore-and jasmonate-induced volatile organic compounds (VOCs), which mediate indirect defense, must provide reliable information for predators that frequently learn to associate their release with feeding herbivores. Yet little is known about variation of these cues within populations of native plants, on a scale encountered by predators.• We examined variation in herbivore-elicited VOC emissions and patterns of herbivore-induced jasmonate signaling from accessions of Nicotiana attenuata cooccurring in a native population. VOC emissions elicited by herbivore oral secretions (OS) and by methyl jasmonate (MJ) were characterized using gas chromatographymass spectrometry (GC-MS), high-resolution two-dimensional gas chromatographytime-of-flight mass spectrometry (GCxGC-ToF-MS) and micro-hydrolysis and micro-hydrogenation reactions.• Accessions varied in emissions of abundant (trans-α-bergamotene, α-duprezianene, trans-β-ocimene, and cis-3-hexenol) and total detectable VOCs, as well as the accumulation of jasmonates, the jasmonate antagonist salicylic acid (SA), abscisic acid (ABA) and jasmonate signaling-related transcripts after OS elicitation. Yet MJ treatment exacerbated differences in VOC emission, suggesting that much variation in VOC emission is caused by processes downstream of jasmonate signaling.• Co-occurring N. attenuata plants emit different VOCs following simulated herbivore elicitation as a result in part of differences in jasmonate production and responsiveness, which could reduce the effectiveness of induced indirect defense. IntroductionWild plants use many strategies to survive herbivore attack, including the constitutive or inducible production of toxic and antidigestive compounds (direct defenses); attraction, via volatile compounds or rewards such as extrafloral nectar, of predators and parasitoids of herbivores (indirect defenses); physical barriers to herbivore feeding; and enhanced growth or sugar reallocation, to ensure sufficient energy stores for reproduction regardless of tissue loss to herbivores (Constabel, 1999;Schwachtje & Baldwin, 2008). Indirect defenses mediated by induced volatile signaling can be a particularly efficient strategy, because the investment of fitness-limiting resources to produce volatile compounds is probably less than that required to activate direct defenses (Gershenzon, 1994; Halitschke et al., 2000). The protection afforded by indirect defenses, which can completely remove or disable herbivores at an early stage of attack, can be greater than that resulting from the deployment of direct defenses, which affects herbivore growth and preference but usually does not cause adapted herbivores to leave the plant (Kessler & Baldwin, 2001;Steppuhn et al., 2004).Plants of the native tobacco Nicotiana attenuata (Solanaceae) germinate after fires from long-lived seed banks to form monocultures in the Great Basin desert, where they are attacked by an unpredictable herbivore community. Feeding by larvae of Manduca sexta and Manduca quinquemaculata (Lepidopter...

SummarySeed growth and accumulation of storage products relies on the delivery of sucrose from the maternal to the filial tissues. The transport route is hidden inside the seed and has never been visualized in vivo. Our approach, based on high-field nuclear magnetic resonance and a custom made

An attempt has been made to define the extent to which metabolic flux in central plant metabolism is reflected by changes in the transcriptome and metabolome, based on an analysis of in vitro cultured immature embryos of two oilseed rape (Brassica napus) accessions which contrast for seed lipid accumulation. Metabolic flux analysis (MFA) was used to constrain a flux balance metabolic model which included 671 biochemical and transport reactions within the central metabolism. This highly confident flux information was eventually used for comparative analysis of flux vs. transcript (metabolite). Metabolite profiling succeeded in identifying 79 intermediates within the central metabolism, some of which differed quantitatively between the two accessions and displayed a significant shift corresponding to flux. An RNA-Seq based transcriptome analysis revealed a large number of genes which were differentially transcribed in the two accessions, including some enzymes/proteins active in major metabolic pathways. With a few exceptions, differential activity in the major pathways (glycolysis, TCA cycle, amino acid, and fatty acid synthesis) was not reflected in contrasting abundances of the relevant transcripts. The conclusion was that transcript abundance on its own cannot be used to infer metabolic activity/fluxes in central plant metabolism. This limitation needs to be borne in mind in evaluating transcriptome data and designing metabolic engineering experiments.