Jasmonic acid (JA) is a critical hormonal regulator of plant growth and defense. To advance our understanding of the architecture and dynamic regulation of the JA gene regulatory network, we ...performed a high-resolution RNA-seq time series of methyl JA-treated Arabidopsis thaliana at 15 time points over a 16-h period. Computational analysis showed that methyl JA (MeJA) induces a burst of transcriptional activity, generating diverse expression patterns over time that partition into distinct sectors of the JA response targeting specific biological processes. The presence of transcription factor (TF) DNA binding motifs correlated with specific TF activity during temporal MeJA-induced transcriptional reprogramming. Insight into the underlying dynamic transcriptional regulation mechanisms was captured in a chronological model of the JA gene regulatory network. Several TFs, including MYB59 and bHLH27, were uncovered as early network components with a role in pathogen and insect resistance. Analysis of subnetworks surrounding the TFs ORA47, RAP2.6L, MYB59, and ANAC055, using transcriptome profiling of overexpressors and mutants, provided insights into their regulatory role in defined modules of the JA network. Collectively, our work illuminates the complexity of the JA gene regulatory network, pinpoints and validates previously unknown regulators, and provides a valuable resource for functional studies on JA signaling components in plant defense and development.
Global food production is set to keep increasing despite a predicted decrease in total arable land 1. To achieve higher production, denser planting will be required on increasingly degraded soils. ...When grown in dense stands, crops elongate and raise their leaves in an effort to reach sunlight, a process termed shade avoidance 2. Shade is perceived by a reduction in the ratio of red (R) to far-red (FR) light and results in the stabilization of a class of transcription factors known as PHYTOCHROME INTERACTING FACTORS (PIFs) 3, 4. PIFs activate the expression of auxin biosynthesis genes 4, 5 and enhance auxin sensitivity 6, which promotes cell-wall loosening and drives elongation growth. Despite our molecular understanding of shade-induced growth, little is known about how this developmental program is integrated with other environmental factors. Here, we demonstrate that low levels of NaCl in soil strongly impair the ability of plants to respond to shade. This block is dependent upon abscisic acid (ABA) signaling and the canonical ABA signaling pathway. Low R:FR light enhances brassinosteroid (BR) signaling through BRASSINOSTEROID SIGNALING KINASE 5 (BSK5) and leads to the activation of BRI1 EMS SUPPRESSOR 1 (BES1). ABA inhibits BSK5 upregulation and interferes with GSK3-like kinase inactivation by the BR pathway, thus leading to a suppression of BES1:PIF function. By demonstrating a link between light, ABA-, and BR-signaling pathways, this study provides an important step forward in our understanding of how multiple environmental cues are integrated into plant development.
•Low-level soil salinity inhibits plant shade avoidance•The effect of salt is dependent upon abscisic acid•Salt antagonizes the shade-mediated upregulation of brassinosteroid signaling
Intensively farmed crops often experience multiple stresses simultaneously. Here, Hayes et al. show that low-level soil salinity suppresses shade avoidance in plants. Through investigation of the mechanisms underlying this trait, they uncover a regulatory pathway that converges at the level of brassinosteroid signaling.
Summary
Plants are known to be responsive to volatiles, but knowledge about the molecular players involved in transducing their perception remains scarce. We study the response of Arabidopsis ...thaliana to E‐2‐hexenal, one of the green leaf volatiles (GLV) that is produced upon wounding, herbivory or infection with pathogens. We have taken a transcriptomics approach to identify genes that are induced by E‐2‐hexenal, but not by defence hormones or other GLVs. Furthermore, by studying the promoters of early E‐2‐hexenal‐induced genes we determined that the only statistically enriched cis‐element was the W‐box motif. Since members of the plant‐specific family of WRKY transcription factors act in trans on this cis‐element, we focused on WRKY6, 40 and 53 that were most strongly induced by E‐2‐hexenal. Root elongation of Arabidopsis seedlings of the wrky40 wrky6 double mutant was much less inhibited than in wt plants, similar to the E‐2‐hexenal‐responsive mutant her1, which is perturbed in γ‐amino butyric acid (GABA) metabolism. The induction of several of the E‐2‐hexenal‐specific genes was much higher in the wrky40, wrky6 or wrky40 wrky6 mutants, including GAD4, a glutamate decarboxylase that catalyzes the formation of GABA from glutamate. In conclusion, WRKY6 and 40 seem to act as important players transducing E‐2‐hexenal perception.
Significance Statement
Plants produce green leaf volatiles (GLVs) in response to wounding or infection, and in turn plants respond to GLVs to mount defense responses. Here we identify several genes in Arabidopsis that are specifically induced by the GLV E‐2‐hexenal providing much needed markers for GLV signalling research.
The interactions of plants with their pollinators are thought to be a driving force in the evolution of angiosperms. Adaptation to a new pollinator involves coordinated changes in multiple floral ...traits controlled by multiple genes. Surprisingly, such complex genetic shifts have happened numerous times during evolution. Here we report on the genetic basis of the changes in one such trait, floral scent emission, in the genus Petunia (Solanaceae). The increase in the quantity and complexity of the volatiles during the shift from bee to hawkmoth pollination was due to de novo expression of the genes encoding benzoic acid/salicylic acid carboxyl methyltransferase (BSMT) and benzoyl-CoA:benzylalcohol/2-phenylethanol benzoyltransferase (BPBT) together with moderately increased transcript levels for most enzymes of the phenylpropanoid/benzenoid pathway. Loss of cinnamate-CoA ligase (CNL) function as well as a reduction in the expression of the MYB transcription factor ODO1 explain the loss of scent during the transition from moth to hummingbird pollination. The CNL gene in the hummingbird-adapted species is inactive due to a stop codon, but also appears to have undergone further degradation over time. Therefore, we propose that loss of scent happened relatively early in the transition toward hummingbird pollination, and probably preceded the loss of UV-absorbing flavonols. The discovery that CNL is also involved in the loss of scent during the transition from outcrossing to selfing in Capsella (Brassicaceae) (see the accompanying paper) raises interesting questions about the possible causes of deep evolutionary conservation of the targets of evolutionary change.
•Structural genes BSMT and BPBT cause gain of scent during bee-to-moth pollination•CNL was inactivated and severely degraded during moth-to-hummingbird pollination•CNL is a target of evolutionary change across angiosperms•Identifying functional mutations can help in the ordering of speciation events
Floral scent is an important signal for pollinators. Amrad et al. identify structural genes involved in the gain and loss of scent during shifts from bee to hawkmoth to hummingbird pollination in Petunia. The identification of such speciation genes provides insight into the process of speciation.
During insect feeding, a complex interaction takes place at the feeding site, with plants deciphering molecular information associated with the feeding herbivore, resulting in the upregulation of the ...appropriate defenses, and the herbivore avoiding or preventing these defenses from taking effect. Whiteflies can feed on plants without causing significant damage to mesophyll cells, making their detection extra challenging for the plant. However, whiteflies secrete honeydew that ends up on the plant surface at the feeding site and on distal plant parts below the feeding site. We reasoned that this honeydew, since it is largely of plant origin, may contain molecular information that alerts the plant, and we focused on the defense hormone salicylic acid (SA). First, we analyzed phloem sap from tomato plants, on which the whiteflies are feeding, and found that it contained salicylic acid (SA). Subsequently, we determined that in honeydew more than 80 % of SA was converted to its glycoside (SAG). When whiteflies were allowed to feed from an artificial diet spiked with labeled SA, labeled SAG also was produced. However, manually depositing honeydew on undamaged plants resulted still in a significant increase in endogenous free SA. Accordingly, transcript levels of PR1a, an SA marker gene, increased whereas those of PI-II, a jasmonate marker gene, decreased. Our results indicate that whiteflies manipulate the SA levels within their secretions, thus influencing the defense responses in those plant parts that come into contact with honeydew.
The WD40 proteins ANTHOCYANIN11 (AN11) from petunia (Petunia hybrida) and TRANSPARENT TESTA GLABRA1 (TTG1) from Arabidopsis thaliana and associated basic helix-loop-helix (bHLH) and MYB transcription ...factors activate a variety of differentiation processes. In petunia petals, AN11 and the bHLH protein AN1 activate, together with the MYB protein AN2, anthocyanin biosynthesis and, together with the MYB protein PH4, distinct genes, such as PH1 and PH5, that acidify the vacuole. To understand how AN1 and AN11 activate anthocyanin biosynthetic and PH genes independently, we isolated PH3. We found that PH3 is a target gene of the AN11-AN1-PH4 complex and encodes a WRKY protein that can bind to AN11 and is required, in a feed-forward loop, together with AN11-AN1-PH4 for transcription of PH5. PH3 is highly similar to TTG2, which regulates hair development, tannin accumulation, and mucilage production in Arabidopsis. Like PH3, TTG2 can bind to petunia AN11 and the Arabidopsis homolog TTG1, complement ph3 in petunia, and reactivate the PH3 target gene PH5. Our findings show that the specificity of WD40-bHLH-MYB complexes is in part determined by interacting proteins, such as PH3 and TTG2, and reveal an unanticipated similarity in the regulatory circuitry that controls petunia vacuolar acidification and Arabidopsis hair development.
Key message
This work adds a new player, HER2, downstream of the perception of
E-2
-hexenal, a green leaf volatile, and shows that
E-2
-hexenal specifically changes the redox status of the ...mitochondria.
It is widely accepted that plants produce and respond to green leaf volatiles (GLVs), but the molecular components involved in transducing their perception are largely unknown. The GLV
E
-2-hexenal inhibits root elongation in seedlings and, using this phenotype, we isolated
E
-2-
he
xenal
r
esponse (
her
)
Arabidopsis thaliana
mutants. Using map-based cloning we positioned the
her2
mutation to the At5g63620 locus, resulting in a phenylalanine instead of serine on position 223. Knockdown and overexpression lines of
HER2
confirmed the role of
HER2
, which encodes an oxidoreductase, in the responsiveness to
E
-2-hexenal. Since
E
-2-hexenal is a reactive electrophile species, which are known to influence the redox status of cells, we utilized redox sensitive GFP2 (roGFP2) to determine the redox status of
E
-2-hexenal-treated root cells. Since the signal peptide of HER2 directed mCherry to the mitochondria, we targeted the expression of roGFP2 to this organelle besides the cytosol.
E
-2-hexenal specifically induced a change in the redox status in the mitochondria. We did not see a difference in the redox status in
her2
compared to wild-type
Arabidopsis
. Still, the mitochondrial redox status did not change with
Z-
3-hexenol, another abundant GLV. These results indicate that HER2 is involved in transducing the perception of
E
-2-hexenal, which changes the redox status of the mitochondria.
Huanglongbing (HLB) is a destructive disease, associated with psyllid-transmitted phloem-restricted pathogenic bacteria, which is seriously endangering citriculture worldwide. It affects all citrus ...species and cultivars regardless of the rootstock used, and despite intensive research in the last decades, there is no effective cure to control either the bacterial species (
Liberibacter spp.) or their insect vectors (
and
). Currently, the best attempts to manage HLB are based on three approaches: (i) reducing the psyllid population by intensive insecticide treatments; (ii) reducing inoculum sources by removing infected trees, and (iii) using nursery-certified healthy plants for replanting. The economic losses caused by HLB (decreased fruit quality, reduced yield, and tree destruction) and the huge environmental costs of disease management seriously threaten the sustainability of the citrus industry in affected regions. Here, we have generated genetically modified sweet orange lines to constitutively emit (
)-β-caryophyllene, a sesquiterpene repellent to
, the main HLB psyllid vector. We demonstrate that this alteration in volatile emission affects behavioral responses of the psyllid in olfactometric and no-choice assays, making them repellent/less attractant to the HLB vector, opening a new alternative for possible HLB control in the field.
Thermophilic fungi have the potential to produce industrial-relevant thermostable enzymes, in particular for the degradation of plant biomass. Sordariales is one of the few fungal orders containing ...several thermophilic taxa, of which many have been associated with the production of thermostable enzymes. The evolutionary affiliation of Sordariales fungi, especially between thermophiles and non-thermophilic relatives, is however poorly understood. Phylogenetic analysis within the current study was based on sequence data, derived from a traditional Sanger and highly multiplexed targeted next generation sequencing approach of 45 isolates. The inferred phylogeny and detailed growth analysis rendered the trait ‘thermophily’ as polyphyletic within Chaetomiaceae (Sordariales, Sordariomycetes), and characteristic to: Myceliophthora spp., Thielavia terrestris, Chaetomium thermophilum, and Mycothermus thermophilus. Compared to mesophiles, the isolates within thermophilic taxa produced enzyme mixtures with the highest thermostability of known cellulase activities. Temperature profiles of the enzyme activities correlated strongly with the optimal growth temperatures of the isolates but not with their phylogenetic relationships. This strong correlation between growth and enzyme characteristics indicated that detailed analysis of growth does give predictive information on enzyme physiology. The variation in growth and enzyme characteristics reveals these fungi as an excellent platform to better understand fungal thermophily and enzyme thermostability.
•RPB2 (>3 kb) of Sordariales isolates were sequenced using next generation sequencing.•Complete RPB2 sequences are more informative than ITS, LSU, EF1, and EF3 sequences.•The trait thermophily was rendered polyphyletic in Chaetomiaceae.•Thermophiles compared to mesophiles produce the most thermostable cellulases.•Optimal growth temperatures give predictive information on enzyme thermostability.
Virus discovery combining sequence unbiased amplification with next generation sequencing is now state-of-the-art. We have previously determined that the performance of the unbiased amplification ...technique which is operational at our institute, VIDISCA-454, is efficient when respiratory samples are used as input. The performance of the assay is, however, not known for other clinical materials like blood or stool samples. Here, we investigated the sensitivity of VIDISCA-454 with feces-suspensions and serum samples that are positive and that have been quantified for norovirus and human immunodeficiency virus type 1, respectively. The performance of VIDISCA-454 in serum samples was equal to its performance in respiratory material, with an estimated lower threshold of 1,000 viral genome copies. The estimated threshold in feces-suspension is around 200,000 viral genome copies. The decreased sensitivity in feces suspension is mainly due to sequences that share no recognizable identity with known sequences. Most likely these sequences originate from bacteria and phages which are not completely sequenced.
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