ZEITLUPE facilitates the rhythmic movements of Nicotiana attenuata flowers.

Circadian organ movements are ubiquitous in plants. These rhythmic outputs are thought to be regulated by the circadian clock and auxin signalling, but the underlying mechanisms have not been clarified. Flowers of Nicotiana attenuata change their orientation during the daytime through a 140° arc to balance the need for pollinators and the protection of their reproductive organs. This rhythmic trait is under the control of the circadian clock and results from bending and re-straightening movements of the pedicel, stems that connect flowers to the inflorescence. Using an explant system that allowed pedicel growth and curvature responses to be characterized with high spatial and temporal resolution, we demonstrated that this movement is organ autonomous and mediated by auxin. Changes in the growth curvature of the pedicel are accompanied by an auxin gradient and dorsiventral asymmetry in auxin-dependent transcriptional responses; application of auxin transport inhibitors influenced the normal movements of this organ. Silencing the expression of the circadian clock component ZEITLUPE (ZTL) arrested changes in the growth curvature of the pedicel and altered auxin signalling and responses. IAA19-like, an Aux/IAA transcriptional repressor that is circadian regulated and differentially expressed between opposite tissues of the pedicel, and therefore possibly involved in the regulation of changes in organ curvature, physically interacted with ZTL. Together, these results are consistent with a direct link between the circadian clock and the auxin signalling pathway in the regulation of this rhythmic floral movement.

Whole-genome-based revisit of Photorhabdus phylogeny: proposal for the elevation of most Photorhabdus subspecies to the species level and description of one novel species Photorhabdus bodei sp. nov., and one novel subspecies Photorhabdus laumondii subsp. clarkei subsp. nov.

Bacterial symbionts are crucial for the infectivity and success of entomopathogenic nematodes as biological control agents. The current understanding of the symbiotic relationships is limited by taxonomic uncertainties. Here, we used whole-genome sequencing and traditional techniques to reconstruct the phylogenetic relationships between all described Photorhabdus species and subspecies as well as 11 newly isolated symbiotic bacteria of Heterorhabditis nematodes, including the unreported bacterial partner of H. beicherriana. In silico DNA-DNA hybridization, orthologous average nucleotide identity and nucleotide sequence identity of concatenated housekeeping genes scores were calculated and set into relation with current cut-off values for species delimitation in bacteria. Sequence data were complemented with biochemical and chemotaxonomic markers, and ribosomal protein fingerprinting profiles. This polyphasic approach resolves the ambiguous taxonomy of Photorhabdusand lead to the proposal for the elevation of most of them into a higher taxon and the creation of several new taxa: 15 new species, one of which is newly described: Photorhabdus bodei sp. nov. (type strain LJ24-63T=DSM 105690T=CCOS 1159T) and the other 14 arise through the proposal of elevating already described subspecies to species, and are proposed to be renamed as follows: Photorhabdus asymbioticasubsp. australis as Photorhabdus australis sp. nov., Photorhabdus luminescenssubsp. akhurstii as Photorhabdus akhurstii sp. nov., Photorhabdus luminescenssubsp. caribbeanensis as Photorhabdus caribbeanensis sp. nov., Photorhabdus luminescenssubsp. hainanensis as Photorhabdus hainanensis sp. nov., Photorhabdus luminescenssubsp. kayaii as Photorhabdus kayaii sp. nov., Photorhabdus luminescenssubsp. kleinii as Photorhabdus kleinii sp. nov., Photorhabdus luminescenssubsp. namnaonensis as Photorhabdus namnaonensis sp. nov., Photorhabdus luminescenssubsp. noenieputensis as Photorhabdus noenieputensis sp. nov., Photorhabdus luminescenssubsp.laumondii as Photorhabdus laumondii sp. nov., Photorhabdus temperatasubsp. cinerea as Photorhabdus cinerea sp. nov., Photorhabdus temperatasubsp. khanii as Photorhabdus khanii sp. nov., Photorhabdus temperatasubsp. stackebrandtii as Photorhabdus stackebrandtii sp. nov., Photorhabdus temperatasubsp. tasmaniensis as Photorhabdus tasmaniensis sp. nov., and Photorhabdus temperatasubsp. thracensis as Photorhabdus thracensis sp. nov. In addition, we propose the creation of two new subspecies, one of which arises through the reduction of rank: Photorhabdus laumondii subsp. laumondii comb. nov. (basonym: P. luminescenssubsp. laumondii) and the second one is newly described: Photorhabdus laumondii subsp. clarkei subsp. nov. (type strain BOJ-47T=DSM 105531T=CCOS 1160T). Finally, we propose to emend the description of three species, which results from the proposal of elevating three subspecies to the species status: Photorhabdus asymbiotica, Photorhabdus temperata and Photorhabdus luminescens, formerly classified as Photorhabdus asymbioticasubsp. asymbiotica, Photorhabdus temperatasubsp.temperata and Photorhabdus luminescenssubsp. luminescens, respectively.

Auxin Is Rapidly Induced by Herbivore Attack and Regulates a Subset of Systemic, Jasmonate-Dependent Defenses.

Plant responses to herbivore attack are regulated by phytohormonal networks. To date, the role of the auxin indole-3-acetic acid (IAA) in this context is not well understood. We quantified and manipulated the spatiotemporal patterns of IAA accumulation in herbivore-attacked Nicotiana attenuata plants to unravel its role in the regulation of plant secondary metabolism. We found that IAA is strongly, rapidly, and specifically induced by herbivore attack. IAA is elicited by herbivore oral secretions and fatty acid conjugate elicitors and is accompanied by a rapid transcriptional increase of auxin biosynthetic YUCCA-like genes. IAA accumulation starts 30 to 60 s after local induction and peaks within 5 min after induction, thereby preceding the jasmonate (JA) burst. IAA accumulation does not require JA signaling and spreads rapidly from the wound site to systemic tissues. Complementation and transport inhibition experiments reveal that IAA is required for the herbivore-specific, JA-dependent accumulation of anthocyanins and phenolamides in the stems. In contrast, IAA does not affect the accumulation of nicotine or 7-hydroxygeranyllinalool diterpene glycosides in the same tissue. Taken together, our results uncover IAA as a rapid and specific signal that regulates a subset of systemic, JA-dependent secondary metabolites in herbivore-attacked plants.

Leaf-herbivore attack reduces carbon reserves and regrowth from the roots via jasmonate and auxin signaling.

Herbivore attack leads to resource conflicts between plant defensive strategies. Photoassimilates are required for defensive compounds and carbon storage below ground and may therefore be depleted or enriched in the roots of herbivore-defoliated plants. The potential role of belowground tissues as mediators of induced tolerance-defense trade-offs is unknown. We evaluated signaling and carbohydrate dynamics in the roots of Nicotiana attenuata following Manduca sexta attack. Experimental and natural genetic variability was exploited to link the observed metabolite patterns to plant tolerance and resistance. Leaf-herbivore attack decreased sugar and starch concentrations in the roots and reduced regrowth from the rootstock and flower production in the glasshouse and the field. Leaf-derived jasmonates were identified as major regulators of this root-mediated resource-based trade-off: lower jasmonate levels were associated with decreased defense, increased carbohydrate levels and improved regrowth from the rootstock. Application and transport inhibition experiments, in combination with silencing of the sucrose non-fermenting (SNF) -related kinase GAL83, indicated that auxins may act as additional signals that regulate regrowth patterns. In conclusion, our study shows that the ability to mobilize defenses has a hidden resource-based cost below ground that constrains defoliation tolerance. Jasmonate- and auxin-dependent mechanisms may lead to divergent defensive plant strategies against herbivores in nature.

Induced immunity against belowground insect herbivores- activation of defenses in the absence of a jasmonate burst.

Roots respond dynamically to belowground herbivore attack. Yet, little is known about the mechanisms and ecological consequences of these responses. Do roots behave the same way as leaves, or do the paradigms derived from aboveground research need to be rewritten? This is the central question that we tackle in this article. To this end, we review the current literature on induced root defenses and present a number of experiments on the interaction between the root herbivore Diabrotica virgifera and its natural host, maize. Currently, the literature provides no clear evidence that plants can recognize root herbivores specifically. In maize, mild mechanical damage is sufficient to trigger a root volatile response comparable to D. virgifera induction. Interestingly, the jasmonate (JA) burst, a highly conserved signaling event following leaf attack, is consistently attenuated in the roots across plant species, from wild tobacco to Arabidopsis. In accordance, we found only a weak JA response in D. virgifera attacked maize roots. Despite this reduction in JA-signaling, roots of many plants start producing a distinct suite of secondary metabolites upon attack and reconfigure their primary metabolism. We, therefore, postulate the existence of additional, unknown signals that govern induced root responses in the absence of a jasmonate burst. Surprisingly, despite the high phenotypic plasticity of plant roots, evidence for herbivore-induced resistance below ground is virtually absent from the literature. We propose that other defensive mechanisms, including resource reallocation and compensatory growth, may be more important to improve plant immunity below ground.