Can micro-guidewire advancement forces predict clot consistency and location to assist the first-line technique for mechanical thrombectomy?

BACKGROUND

The identification of specific clot characteristics before mechanical thrombectomy (MTB) might allow the selection of the most effective first-line technique, thus potentially improving the procedural outcome. We aimed to evaluate if the microwire push forces could extrapolate information on clot consistency and extension before MTB, based on clot mechanical properties.

METHODS

We measured in vitro the forces exerted on the proximal extremity of the guidewire during the advancement and retrieval of the guidewire through clot analogs of different compositions. In addition, we analyzed the forces exerted on the guidewire to extrapolate information about the location of the proximal and distal extremities of the clot analogs.

RESULTS

The maximum forces recorded during the whole penetration phase were significantly different for hard and soft clots (median values, 55.6 mN vs 15.4 mN, respectively; P<0.0001). The maximum slope of the force curves recorded during the advancement of the guidewire for the first 3 s of penetration also significantly differentiated soft from hard clot analogs (7.6 mN/s vs 23.9 mN/s, respectively; P<0.0001). In addition, the qualitative analysis of the shape of the force curves obtained during the advancement and retrieval of the guidewire showed a good potential for the identification of the proximal and distal edges of the clot analogs.

CONCLUSION

Our results demonstrated that it was possible to differentiate between soft and hard clot analogs. Furthermore, force measurements could give important information about the location of the clot extremities. Such an approach might support the selection of the first-line MTB technique, with the potential to improve the outcome.

Double stent-retriever technique for mechanical thrombectomy: a systematic review and meta-analysis

BACKGROUND

Mechanical thrombectomy using a double stent-retriever technique has recently been described for the treatment of acute ischemic stroke, but its efficacy and safety are not well established.

PURPOSE

The aim of this systematic review and meta-analysis was to evaluate reports of the use of double stent-retriever during the endovascular treatment of patients with ischemic stroke.

DATA SOURCES

The PubMed, Embase, Web of Science and Scopus databases were searched to identify all studies (clinical trials, cohorts series and case reports) investigating the utility of double stent-retriever for the treatment of stroke. The study is reported in accordance with PRISMA 2020 guidelines and was prospectively registered in PROSPERO (BLINDED FOR PEER REVIEW).

STUDY SELECTION

17 studies involving a total of 128 patients with large vessel occlusions predominantly in the anterior circulation (93.0%) were identified.

DATA ANALYSIS

Outcomes of interest were the prevalence of successful recanalization (mTICI ≥2b) and a first-pass effect following double stent-retriever, as well as complications such as iatrogenic dissections and subarachnoid hemorrhage. Data were pooled using a random-effects model.

DATA SYNTHESIS

Double stent-retriever was used as a rescue strategy in occlusions refractory to conventional endovascular treatment in 68.7% (88/128) of patients and as a first-line strategy in 31.3% (40/128) patients. Double stent-retriever achieved an overall final mTICI ≥2b in 92.6% cases with a first-pass effect of 76.6%. The complication rate remained low, with 0.37% dissection and 1.56% subarachnoid hemorrhage.

LIMITATIONS

Limitations of the study include (1) a large number of case reports or small series, (2) a meta-analysis of proportions with no statistical comparison to a control group, and (3) the lack of access to patient-level data.

CONCLUSIONS

Our findings suggest that double stent-retriever thrombectomy may be safe and associated with good recanalization outcomes, but prospective comparative studies are needed to determine which patients may benefit from this endovascular procedure.

ABBREVIATIONS

AICH = asymptomatic intracranial hemorrhage; AIS = acute ischemic stroke; DSR = double stent-retriever; FPE = first pass effect; ICH = intracranial hemorrhage; LVO = large vessel occlusion; MT = mechanical thrombectomy; SAH = subarachnoid hemorrhage; SICH = symptomatic intracranial hemorrhage; SSR = single stent-retriever.

Effectiveness of the preventive administration of vasoactive amines in counterbalancing significant patient blood pressure drops following nimodipine administration during mechanical thrombectomy procedures

BACKGROUND

Focal vasospasm (FV) of the occluded vessel can occur during the endovascular treatment of acute ischemic stroke (AIS). Nimodipine is commonly used to treat vasospasm and can play a role in distinguishing it from artery narrowing due to iatrogenic dissection or residual clot. However, nimodipine administration can result in arterial hypotension and subsequent enlargement of the ischemic core.

OBJECTIVE

To assess the efficacy of preventive and continuous vasoactive amine infusion to counterbalance nimodipine-induced hypotension.

METHODS

We reviewed data from a prospective registry of patients treated for AIS between January 2019 and January 2022 who were administered nimodipine. All patients were equipped with an arterial cannula for invasive blood pressure measurement and given vasoactive amines preemptively before general anesthesia and throughout the procedure. Data obtained from invasive monitoring of mean arterial blood pressure (MABP) in a time-lapse of 25 min before and after nimodipine administration were analyzed.

RESULTS

MABP significantly decreased after nimodipine administration but remained within the recommended range (81.79 ± 0.49 mmHg). Nimodipine was effective in reducing FV caused by stent retriever passage in 76.3% of cases. Furthermore, it proved valuable in diagnosing iatrogenic dissection (9.2%), residual clot (10.5%), or intracranial stenosis (4%).

CONCLUSIONS

Infusion of vasoactive amines effectively counteracted the intraarterial nimodipine effect, thus avoiding frank arterial hypotension during endovascular treatment. Nimodipine has been useful in differentiating the diagnosis of FV resulting from mechanical thrombectomy and other potential causes, such as iatrogenic dissection or residual clot.

Subtilase-mediated biogenesis of the expanded family of SERINE RICH ENDOGENOUS PEPTIDES

Plant signalling peptides are typically released from larger precursors by proteolytic cleavage to regulate plant growth, development and stress responses. Recent studies reported the characterization of a divergent family of Brassicaceae-specific peptides, SERINE RICH ENDOGENOUS PEPTIDES (SCOOPs), and their perception by the leucine-rich repeat receptor kinase MALE DISCOVERER 1-INTERACTING RECEPTOR-LIKE KINASE 2 (MIK2). Here, we reveal that the SCOOP family is highly expanded, containing at least 50 members in the Columbia-0 reference Arabidopsis thaliana genome. Notably, perception of these peptides is strictly MIK2-dependent. How bioactive SCOOP peptides are produced, and to what extent their perception is responsible for the multiple physiological roles associated with MIK2 are currently unclear. Using N-terminomics, we validate the N-terminal cleavage site of representative PROSCOOPs. The cleavage sites are determined by conserved motifs upstream of the minimal SCOOP bioactive epitope. We identified subtilases necessary and sufficient to process PROSCOOP peptides at conserved cleavage motifs. Mutation of these subtilases, or their recognition motifs, suppressed PROSCOOP cleavage and associated overexpression phenotypes. Furthermore, we show that higher-order mutants of these subtilases show phenotypes reminiscent of mik2 null mutant plants, consistent with impaired PROSCOOP biogenesis, and demonstrating biological relevance of SCOOP perception by MIK2. Together, this work provides insights into the molecular mechanisms underlying the functions of the recently identified SCOOP peptides and their receptor MIK2.

Cancer outpatients during the COVID-19 pandemic: what Oncoral has to teach us about medical drug use and the perception of telemedicine

PURPOSE

The COVID-19 pandemic has disrupted healthcare access and telemedicine has been widely deployed. The aim of this study is to assess the impact of this health crisis on treatment consumption and telemedicine development in outpatients treated by oral anti-cancer agents and followed by the Oncoral hospital/community multidisciplinary program where continuity care is maintained by a pharmacist/nurse pair.

METHODS

A prospective monocentric study was conducted among cancer patients who received Oncoral telephone follow-up during the 1st lockdown in France using a 56-item questionnaire which covered sociodemographic data, patient medication management, and telehealth.

RESULTS

178 patients received Oncoral follow-up during the 1st lockdown and 67.4% responded to the questionnaire. During lockdown, 9.2% of patients took medication or CAM for fatigue, 6.7% for mood alteration, 10.8% for sleep disorder, 11.7% for stress and anxiety, and 12.5% to get more energy. Homeopathy consumption was triggered by the pandemic. Habits about getting drugs from the pharmacy changed significantly (p < 0.001), while other treatment habits did not. 83% of patients were satisfied by the telephone follow-up established, 69% would be in favor of repeating this in case of a new epidemic wave. Those most in favor of using telemedicine seemed to be the youngest (p < 0.001), with several dependent children (p < 0.007), high school degree or higher education (p = 0.023), and in work (p < 0.001).

CONCLUSION

Health system reorganization enables to limit the impact of the crisis on patients' drug use in oncology care. Telemedicine is a promising public health tool.

Benchtop evaluation of a double stent retriever thrombectomy technique for acute ischemic stroke treatment

BACKGROUND AND PURPOSE

A mechanical thrombectomy technique using a double stent retriever approach has been reported for the treatment of patients with acute ischemic stroke. The purpose of this study was to perform a benchtop evaluation of the mechanism of action and efficacy of a double-stent retriever approach compared to a single-stent retriever approach.

MATERIALS AND METHODS

In vitro, mechanical thrombectomy procedures were performed in a vascular phantom reproducing an M1-M2 occlusion with two different clot analog consistencies (soft and hard). We compared the double stent retriever approach to the single stent retriever approach and recorded the recanalization rate, distal embolization, and retrieval forces of each mechanical thrombectomy procedure.

RESULTS

The double stent retriever approach achieved a higher recanalization rate and lower embolic complications compared to the single stent retriever approach. This seems to stem from two facts: the greater probability of targeting the correct artery with two stents in the case of bifurcation occlusion, and an improved clot capture mechanism using the double stent retriever approach. However, the double stent retriever was associated with an increased initial retrieval force.

CONCLUSIONS

In vitro evaluation of the mechanism of action of the double stent retriever provided explanations that appear to support the high efficacy of such an approach in patient cohorts and could help operators when selecting the optimal mechanical thrombectomy strategy in cases of arterial occlusions difficult to treat with a single stent retriever.

Aortic Dilatation on the Edge of Dissection-Do We Operate Too Late? The Ratio between Ascending and Descending Aorta DiameteR (RADAR)

(1) Background: There is a need for a novel surrogate marker to ease decision making when facing ascending aortic dilatation. In this article, we study the ratio between ascending and descending aorta diameters as a potential one. (2) Methods: Retrospective observational cohort study, including all the patients who underwent surgery for acute type A aorta dissection (aTAAD) between January 2014 and September 2020 at our center. A total of 50 patients were included. Clinical and demographic data were collected. The anatomical measurements were made including orthogonal maximal diameters of the ascending and descending aorta, post-dissection whole circumference length (post-wCL), post-dissection true lumen circumference length (post-tCL), and surface and sphericity indices of the ascending and descending aorta. Pre-dissection ascending aorta diameter (pre-AAD) and pre-dissection descending aorta diameter (pre-DAD) were calculated as well as the ratio between them and compared with reference values. (3) Results: Of the pre-AAD patients, 96% had smaller than the recommended 55 mm. The ratio between the descending and ascending aorta pre-dissection diameters was significantly smaller compared to the reference value (0.657 ± 0.125 versus 0.745 ± 0.016 with a mean difference of -0.088 and a p < 0.001). (4) Conclusions: The 55 mm threshold for aorta maximal diameter is an insufficient criterion when assessing the risk of dissection. The ratio between DAD and AAD is a parameter worthy of analysis as a tool to stratify the risk of dissection.

Endovascular treatment strategies for simultaneous bilateral anterior circulation occlusions in acute ischemic stroke: A single-center experience and systematic review of the literature

BACKGROUND

Bilateral and simultaneous occlusion of the anterior circulation is a rare event in patients with acute ischemic stroke. Although endovascular treatment is feasible and safe, the endovascular strategy to be used remains a subject of debate.

OBJECTIVE

To assess the different endovascular strategies proposed for the treatment of a bilateral, simultaneous anterior circulation occlusion following acute ischemic stroke.

METHODS

We present a retrospective study of the clinical and radiological records of all patients with a bilateral, simultaneous anterior circulation occlusion treated at our center between January 2019 and December 2022. Following the PRISMA guidelines, we also conducted a systematic review of the literature.

RESULTS

Two patients with a bilateral and simultaneous middle cerebral artery occlusion were treated at our center during the study period. A TICI score ≥2b was obtained in 4 out of 4 occlusions. Modified Rankin Scale (mRS) at 90 days was 0 and 4, respectively. The literature review retrieved reports on 22 patients. The most frequent bilateral occlusion sites were internal carotid artery-middle cerebral artery. The clinical presentation was severe in most patients. A combined thrombectomy technique proved to have the highest number of first-pass recanalization. A TICI ≥2b was obtained in 95% of patients and an mRS ≤2 was found in 31.8% of patients.

CONCLUSIONS

In patients with bilateral and simultaneous occlusion of the anterior circulation, endovascular treatment using a combined technique appears to be rapid and effective. The clinical evolution of this patient population strongly depends on the severity of the onset symptoms.

Near-wall hemodynamic parameters quantification in in vitro intracranial aneurysms with 7 T PC-MRI

OBJECTIVE

Wall shear stress (WSS) and its derived spatiotemporal parameters have proven to play a major role on intracranial aneurysms (IAs) growth and rupture. This study aims to demonstrate how ultra-high field (UHF) 7 T phase contrast magnetic resonance imaging (PC-MRI) coupled with advanced image acceleration techniques allows a highly resolved visualization of near-wall hemodynamic parameters patterns in in vitro IAs, paving the way for more robust risk assessment of their growth and rupture.

MATERIALS AND METHODS

We performed pulsatile flow measurements inside three in vitro models of patient-specific IAs using 7 T PC-MRI. To this end, we built an MRI-compatible test bench, which faithfully reproduced a typical physiological intracranial flow rate in the models.

RESULTS

The ultra-high field 7 T images revealed WSS patterns with high spatiotemporal resolution. Interestingly, the high oscillatory shear index values were found in the core of low WSS vortical structures and in flow stream intersecting regions. In contrast, maxima of WSS occurred around the impinging jet sites.

CONCLUSIONS

We showed that the elevated signal-to-noise ratio arising from 7 T PC-MRI enabled to resolve high and low WSS patterns with a high degree of detail.

Experimental evaluation of the performance of large bore aspiration catheters

BACKGROUND AND PURPOSE

Mechanical thrombectomy using an aspiration catheter (AC) is widely performed in patients with acute ischemic stroke due to large vessel occlusion. AC diameter directly impacts aspiration performance, which has led device companies to develop large bore ACs. The purpose of this study was to evaluate the in vitro performance of several commercially available large bore ACs.

MATERIALS AND METHODS

We conceived an experimental set up to assess tracking force, aspiration flow rate, and distal end tensile force pre- and post-thrombectomy of ACs including Sofia 6 (Microvention Inc., California, USA), React 71 (Medtronic Neurovascular, Irvine, California, USA), Jet 7 (Penumbra Inc, Alameda, California, USA), Catalyst 7 (Stryker Neurovascular, Kalamazoo, Michigan, USA) and Embovac 071 (Johnson & Johnson Medical Ltd, UK).

RESULTS

React 71 and Sofia 6 had significantly lower trackability force compared to the other ACs tested. Distal AC segment tensile force was highest for React 71 and lowest for Jet 7. Jet 7 had the highest internal diameter and the highest aspiration flow rate.

CONCLUSION

The data from this comparative analysis may assist clinicians in selecting the appropriate AC and highlights the need for key performance criteria during the development of next-generation large-bore ACs for optimal AC performance.

Insect egg-induced innate immunity: Who benefits?

Plants perceive the presence of insect eggs deposited on leaves as a cue of imminent herbivore attack. Consequential plant signaling events include the accumulation of salicylic acid and reactive oxygen species, transcriptional reprogramming, and cell death. Interestingly, egg-induced innate immunity shows similarities with immune responses triggered upon recognition of microbial pathogens, and in recent years, it became apparent that egg perception affects plant-microbe interactions. Here, we highlight recent findings on insect egg-induced innate immunity and how egg-mediated signaling impacts plant-microbe interactions. Ecological considerations beg the question: Who benefits from egg perception in these complex interactions?

Spatial heterogeneity of occlusive thrombus in acute ischemic stroke: A systematic review

Following the advent of mechanical thrombectomy, occlusive clots in ischemic stroke have been amply characterized using conventional histopathology. Many studies have investigated the compositional variability of thrombi and the consequences of thrombus composition on treatment response. More recent evidence has emerged about the spatial heterogeneity of the clot or the preferential distribution of its components and compact nature. Here we review this emerging body of evidence, discuss its potential clinical implications, and propose the development of adequate characterization techniques.

Three-dimensional rotational angiography improves mechanical thrombectomy recanalization rate for acute ischaemic stroke due to middle cerebral artery M2 segment occlusions

BACKGROUND

Occlusions of the middle cerebral artery (MCA) M2 segments can be difficult to address with mechanical thrombectomy (MTB) using standard projections and this can affect the final recanalization. Three-dimensional rotational angiography (3D-RA) allows to obtain a 3D model of cerebral vessels in a few seconds and to determine the best two-dimensional (2D) projections to be selected to evaluate and treat cerebrovascular diseases, such as aneurysms or vascular malformations. We aimed to determine if 3D-RA could be applied also in MTB.

METHODS

A retrospective review of two patient cohorts treated during two time periods of 12 months before and after the introduction of 3D-RA use at our institution for MTB in M2 occlusions. Analyses were conducted to compare the two groups for procedural characteristics, such as timing, recanalization rate and complications and clinical outcome.

RESULTS

One hundred acute ischaemic stroke (AIS) patients (3D-RA group = 57; controls = 43) underwent MTB for an M2 occlusion during the two study periods. Recanalization rates were significantly higher in cases treated with 3D-RA. The mean 3D technique thrombectomy time was compared to that of non-3D cases (47 vs. 49 min, respectively).

CONCLUSIONS

Our findings showed that 3D-RA is a useful tool to select specific working projections to AIS patients presenting an M2 occlusion by improving final recanalization compared to standard projections, without increasing the overall procedural time.

The Chemistry of Plant-Insect Egg Interactions

Insect eggs deposited on plants constitute a threat that has led to the evolution of sophisticated defenses. The interactions between insect eggs and plants are governed by a diverse variety of chemicals that inform butterflies about suitable hosts, repel gravid females, alert plants about the presence of an egg, act as signal molecules to induce defenses, directly impair egg development, and indirectly attract egg parasitoids. In recent years, significant progress has been made on the chemical identification, perception and role of compounds associated with oviposition. Knowledge on the genetic basis of oviposition-induced responses is also accumulating. An emerging theme is that insect eggs are not passive structures on leaves but induce complex responses that result from million years of coevolution.

In vitro evaluation of how the presence of the stent retriever and microcatheter influences aspiration parameters in thrombectomy according to their position inside the aspiration catheter

BACKGROUND

Several variations of the combined thrombectomy technique for acute ischemic stroke using a stent retriever and aspiration catheter have been described. The aim of our study was to assess how the presence of the microcatheter and stent retriever affect the basic aspiration parameters, namely, flow rate and aspiration force, depending on their position within the aspiration catheter.

METHODS

Two experimental set-ups were designed to assess changes in flow rate and aspiration force according to the position of the stent retriever and microcatheter within the aspiration catheter.

RESULTS

The transition of the stent retriever and microcatheter from the distal to proximal position resulted in a progressive increase in the flow rate, but with no impact on aspiration force. Additionally, the size of the stent retriever had no significant effect on flow rate changes and the reduction in flow rate was related to the microcatheter diameter. Negative pressure generated inside the aspiration catheter impacted on its distal segment located beyond the radiopaque marker, thus leading to its partial collapse. As a consequence, the measured aspiration force was lower than the theoretical aspiration force level for all tested aspiration catheters.

CONCLUSIONS

In our experimental model, the position of the stent retriever and microcatheter within the aspirator catheter affected the flow rate, but not the aspiration force. Negative pressure generated within the aspiration catheter appeared to determine a partial collapse of the distal segment that resulted in a less effective aspiration force than the theoretical aspiration force level.

Sphingolipids are involved in insect egg-induced cell death in Arabidopsis

In Brassicaceae, hypersensitive-like programmed cell death (HR-like) is a central component of direct defenses triggered against eggs of the large white butterfly (Pieris brassicae). The signaling pathway leading to HR-like in Arabidopsis (Arabidopsis thaliana) is mainly dependent on salicylic acid (SA) accumulation, but downstream components are unclear. Here, we found that treatment with P. brassicae egg extract (EE) triggered changes in expression of sphingolipid metabolism genes in Arabidopsis and black mustard (Brassica nigra). Disruption of ceramide (Cer) synthase activity led to a significant decrease of EE-induced HR-like whereas SA signaling and reactive oxygen species levels were unchanged, suggesting that Cer are downstream activators of HR-like. Sphingolipid quantifications showed that Cer with C16:0 side chains accumulated in both plant species and this response was largely unchanged in the SA-induction deficient2 (sid2-1) mutant. Finally, we provide genetic evidence that the modification of fatty acyl chains of sphingolipids modulates HR-like. Altogether, these results show that sphingolipids play a key and specific role during insect egg-triggered HR-like.

MicroCT Can Characterize Clots Retrieved With Mechanical Thrombectomy From Acute Ischemic Stroke Patients–A Preliminary Report

Background

Characterization of the clot occluding the arteries in acute ischemic stroke received ample attention, in terms of elucidating the relationship between the clot composition, its etiology and its amenability for pharmacological treatment and mechanical thrombectomy approaches. Traditional analytical techniques such as conventional 2D histopathology or electron microscopy sample only small parts of the clot. Visualization and analysis in 3D are necessary to depict and comprehend the overall organization of the clot. The aim of this study is to investigate the potential of microCT for characterizing the clot composition, structure, and organization.

Methods

In a pilot study, we analyzed with microCT clots retrieved from 14 patients with acute ischemic stroke. The following parameters were analyzed: overall clot density, clot segmentation with various density thresholds, clot volume.

Results

Our findings show that human clots are heterogeneous in terms of CT intra-clot density distribution. After fixation in formalin, the clots display a shift toward negative values. On average, we found the mean HU values of red clots retrieved from patients to be −153 HU, with SD = 23.8 HU, for the intermediate clots retrieved from patients −193 HU, SD = 23.7 HU, and for the white clots retrieved from patients −229 HU, SD = 64.8 HU.

Conclusion

Our study shows that volumetric and density analysis of the clot opens new perspectives for clot characterization and for a better understanding of thrombus structure and composition.

Three-dimensional printed moulds to obtain silicone hearts with congenital defects for paediatric heart-surgeon training

OBJECTIVES

Many types of congenital heart disease are amenable to surgical repair or palliation. The procedures are often challenging and require specific surgical training, with limited real-life exposure and often costly simulation options. Our objective was to create realistic and affordable 3D simulation models of the heart and vessels to improve training.

METHODS

We created moulded vessel models using several materials, to identify the material that best replicated human vascular tissue. This material was then used to make more vessels to train residents in cannulation procedures. Magnetic resonance imaging views of a 23-month-old patient with double-outlet right ventricle were segmented using free open-source software. Re-usable moulds produced by 3D printing served to create a silicone model of the heart, with the same material as the vessels, which was used by a heart surgeon to simulate a Rastelli procedure.

RESULTS

The best material was a soft elastic silicone (Shore A hardness 8). Training on the vessel models decreased the residents' procedural time and improved their grades on a performance rating scale. The surgeon evaluated the moulded heart model as realistic and was able to perform the Rastelli procedure on it. Even if the valves were poorly represented, it was found to be useful for preintervention training.

CONCLUSIONS

By using free segmentation software, a relatively low-cost silicone and a technique based on re-usable moulds, the cost of obtaining heart models suitable for training in congenital heart defect surgery can be substantially decreased.

The MIK2/SCOOP Signaling System Contributes to Arabidopsis Resistance Against Herbivory by Modulating Jasmonate and Indole Glucosinolate Biosynthesis

Initiation of plant immune signaling requires recognition of conserved molecular patterns from microbes and herbivores by plasma membrane-localized pattern recognition receptors. Additionally, plants produce and secrete numerous small peptide hormones, termed phytocytokines, which act as secondary danger signals to modulate immunity. In Arabidopsis, the Brassicae-specific SERINE RICH ENDOGENOUS PEPTIDE (SCOOP) family consists of 14 members that are perceived by the leucine-rich repeat receptor kinase MALE DISCOVERER 1-INTERACTING RECEPTOR LIKE KINASE 2 (MIK2). Recognition of SCOOP peptides elicits generic early signaling responses but knowledge on how and if SCOOPs modulate specific downstream immune defenses is limited. We report here that depletion of MIK2 or the single PROSCOOP12 precursor results in decreased Arabidopsis resistance against the generalist herbivore Spodoptera littoralis but not the specialist Pieris brassicae. Increased performance of S. littoralis on mik2-1 and proscoop12 is accompanied by a diminished accumulation of jasmonic acid, jasmonate-isoleucine and indolic glucosinolates. Additionally, we show transcriptional activation of the PROSCOOP gene family in response to insect herbivory. Our data therefore indicate that perception of endogenous SCOOP peptides by MIK2 modulates the jasmonate pathway and thereby contributes to enhanced defense against a generalist herbivore.

Insect eggs trigger systemic acquired resistance against a fungal and an oomycete pathogen

Plants are able to detect insect eggs deposited on leaves. In Arabidopsis, eggs of the butterfly species Pieris brassicae (common name large white) induce plant defenses and activate the salicylic acid (SA) pathway. We previously discovered that oviposition triggers a systemic acquired resistance (SAR) against the bacterial hemibiotroph pathogen Pseudomonas syringae. Here, we show that insect eggs or treatment with egg extract (EE) induce SAR against the fungal necrotroph Botrytis cinerea BMM and the oomycete pathogen Hyaloperonospora arabidopsidis Noco2. This response is abolished in ics1, ald1 and fmo1, indicating that the SA pathway and the N-hydroxypipecolic acid (NHP) pathway are involved. Establishment of EE-induced SAR in distal leaves potentially involves tryptophan-derived metabolites, including camalexin. Indeed, SAR is abolished in the biosynthesis mutants cyp79B2 cyp79B3, cyp71a12 cyp71a13 and pad3-1, and camalexin is toxic to B. cinerea in vitro. This study reveals an interesting mechanism by which lepidopteran eggs interfere with plant-pathogen interactions.

To Balloon or Not to Balloon? The Effects of an Intra-Aortic Balloon-Pump on Coronary Artery Flow during Extracorporeal Circulation Simulating Normal and Low Cardiac Output Syndromes

ECMO is the most frequently used mechanical support for patients suffering from low cardiac output syndrome. Combining IABP with ECMO is believed to increase coronary artery blood flow, decrease high afterload, and restore systemic pulsatile flow conditions. This study evaluates that combined effect on coronary artery flow during various load conditions using an in vitro circuit. In doing so, different clinical scenarios were simulated, such as normal cardiac output and moderate-to-severe heart failure. In the heart failure scenarios, we used peripheral ECMO support to compensate for the lowered cardiac output value and reach a default normal value. The increase in coronary blood flow using the combined IABP-ECMO setup was more noticeable in low heart rate conditions. At baseline, intermediate and severe LV failure levels, adding IABP increased coronary mean flow by 16%, 7.5%, and 3.4% (HR 60 bpm) and by 6%, 4.5%, and 2.5% (HR 100 bpm) respectively. Based on our in vitro study results, combining ECMO and IABP in a heart failure setup further improves coronary blood flow. This effect was more pronounced at a lower heart rate and decreased with heart failure, which might positively impact recovery from cardiac failure.

Acute Stenting and Concomitant Tirofiban Administration for the Endovascular Treatment of Acute Ischemic Stroke Related to Intracranial Artery Dissections: A Single Center Experience and Systematic Review of the Literature

BACKGROUND

Intracranial artery dissection is an uncommon cause of acute ischemic stroke. Although acute stenting of the dissected arterial segment is a therapeutic option, the associated antiplatelet regimen remains a matter of debate.

OBJECTIVES

To evaluate the efficacy and safety of acute intracranial stenting together with concomitant intravenous administration of tirofiban and to perform a systematic review of the literature.

MATERIALS AND METHODS

A single-center, retrospective study of the clinical and radiological records of all patients treated at our center by intracranial stenting in the setting of acute ischemic stroke between January 2010 and December 2020. A systematic review of the literature was conducted according to the PRISMA-P guidelines for relevant publications from January 1976 to December 2020 on intracranial artery dissection treated by stent.

RESULTS

Seven patients with intracranial artery dissections underwent acute stenting with concomitant tirofiban during the study period. Mid-term follow-up showed parent artery patency in 6/7 cases (85.7%). The modified Rankin Score was ≤ 0-2 at 3 months in 5/7 cases (71.4%). The literature review identified 22 patients with intracranial artery dissection treated with acute stenting in association with different antithrombotic therapies. Complete revascularization was obtained in 86.3% of cases with a modified Rankin Score of ≤ 0-2 in 68% of patients at 3-month follow-up.

CONCLUSIONS

Acute intracranial stenting together with intravenous tirofiban administration could be a therapeutic option in patients with intracranial artery dissection and a small ischemic core.

Arabidopsis natural variation in insect egg-induced cell death reveals a role for LECTIN RECEPTOR KINASE-I.1

In Arabidopsis (Arabidopsis thaliana), a hypersensitive-like response (HR-like response) is triggered underneath the eggs of the large white butterfly Pieris brassicae (P. brassicae), and this response is dependent on salicylic acid (SA) accumulation and signaling. Previous reports indicate that the clade I L-type LECTIN RECEPTOR KINASE-I.8 (LecRK-I.8) is involved in early steps of egg recognition. A genome-wide association study was used to better characterize the genetic structure of the HR-like response and discover loci that contribute to this response. We report here the identification of LecRK-I.1, a close homolog of LecRK-I.8, and show that two main haplotypes that explain part of the variation in HR-like response segregate among natural Arabidopsis accessions. Besides, signatures of balancing selection at this locus suggest that it may be ecologically important. Disruption of LecRK-I.1 results in decreased HR-like response and SA signaling, indicating that this protein is important for the observed responses. Furthermore, we provide evidence that LecRK-I.1 functions in the same signaling pathway as LecRK-I.8. Altogether, our results show that the response to eggs of P. brassicae is controlled by multiple LecRKs.

Experimental evaluation of direct thromboaspiration efficacy according to the angle of interaction between the aspiration catheter and the clot

Background

Successful direct thromboaspiration (DTA) is related to several factors such as clot consistency, size, and location. It has also been demonstrated recently that the angle of interaction (AOI) formed by the aspiration catheter and the clot is related to DTA efficacy. The aims of this study were three-fold: (a) to confirm the clinical finding that the AOI formed by the aspiration catheter and the clot influence DTA efficacy; (b) to evaluate to what extent this influence varies according to differences in clot consistency and size; and (c) to validate stent retriever thrombectomy as an effective rescue treatment after DTA failure in the presence of an unfavorable AOI.

Methods

A rigid vascular phantom designed to reproduce a middle cerebral artery trifurcation anatomy with three M2 segments forming different angles with M1 and thrombus analog of different consistencies and sizes was used.

Results

DTA was highly effective for AOIs >125.5°, irrespective of thrombus analog features. However, its efficacy decreased for acute AOIs. Rescue stent retriever thrombectomy was effective in 92.6% of cases of DTA failure.

Conclusions

This in vitro study confirmed that the AOI formed by the aspiration catheter and the thrombus analog influenced DTA efficacy, with an AOI >125.5° related to an effective DTA. Stent retriever thrombectomy was an effective rescue treatment after DTA failure, even in the presence of an unfavorable AOI.

Pieris brassicae eggs trigger interplant systemic acquired resistance against a foliar pathogen in Arabidopsis

Recognition of plant pathogens or herbivores activate a broad-spectrum plant defense priming in distal leaves against potential future attacks, leading to systemic acquired resistance (SAR). Additionally, attacked plants can release aerial or below-ground signals that trigger defense responses, such as SAR, in neighboring plants lacking initial exposure to pathogen or pest elicitors. However, the molecular mechanisms involved in interplant defense signal generation in sender plants and decoding in neighboring plants are not fully understood. We previously reported that Pieris brassicae eggs induce intraplant SAR against the foliar pathogen Pseudomonas syringae in Arabidopsis thaliana. Here we extend this effect to neighboring plants by discovering an egg-induced interplant SAR via mobile root-derived signal(s). The generation of an egg-induced interplant SAR signal requires pipecolic acid (Pip) pathway genes ALD1 and FMO1 but occurs independently of salicylic acid (SA) accumulation in sender plants. Furthermore, reception of the signal leads to accumulation of SA in the recipient plants. In response to insect eggs, plants may induce interplant SAR to prepare for potential pathogen invasion following feeding-induced wounding or to keep neighboring plants healthy for hatching larvae. Our results highlight a previously uncharacterized below-ground plant-to-plant signaling mechanism and reveals genetic components required for its generation.

Phosphatidylcholines from Pieris brassicae eggs activate an immune response in Arabidopsis

Recognition of conserved microbial molecules activates immune responses in plants, a process termed pattern-triggered immunity (PTI). Similarly, insect eggs trigger defenses that impede egg development or attract predators, but information on the nature of egg-associated elicitors is scarce. We performed an unbiased bioactivity-guided fractionation of eggs of the butterfly Pieris brassicae. Nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry of active fractions led to the identification of phosphatidylcholines (PCs). PCs are released from insect eggs, and they induce salicylic acid and H₂O₂ accumulation, defense gene expression and cell death in Arabidopsis, all of which constitute a hallmark of PTI. Active PCs contain primarily C16 to C18-fatty acyl chains with various levels of desaturation, suggesting a relatively broad ligand specificity of cell-surface receptor(s). The finding of PCs as egg-associated molecular patterns (EAMPs) illustrates the acute ability of plants to detect conserved immunogenic patterns from their enemies, even from seemingly passive structures such as eggs.

Stress- and pathway-specific impacts of impaired jasmonoyl-isoleucine (JA-Ile) catabolism on defense signalling and biotic stress resistance

Jasmonate synthesis and signalling are essential for plant defense upregulation upon herbivore or microbial attacks. Stress-induced accumulation of jasmonoyl-isoleucine (JA-Ile), the bioactive hormonal form triggering transcriptional changes, is dynamic and transient because of the existence of potent removal mechanisms. Two JA-Ile turnover pathways operate in Arabidopsis, consisting in cytochrome P450 (CYP94)-mediated oxidation and deconjugation by the amidohydrolases IAR3/ILL6. Understanding their impacts was previously blurred by gene redundancy and compensation mechanisms. Here we address the consequences of blocking these pathways on jasmonate homeostasis and defenses in double-2ah, triple-3cyp mutants, and a quintuple-5ko line deficient in all known JA-Ile-degrading activities. These lines reacted differently to either mechanical wounding/insect attack or fungal infection. Both pathways contributed additively to JA-Ile removal upon wounding, but their impairement had opposite impacts on insect larvae feeding. By contrast, only the ah pathway was essential for JA-Ile turnover upon infection by Botrytis, yet only 3cyp was more fungus-resistant. Despite building-up extreme JA-Ile levels, 5ko displayed near-wild-type resistance in both bioassays. Molecular analysis indicated that restrained JA-Ile catabolism resulted in enhanced defense/resistance only when genes encoding negative regulators were not simultaneously overstimulated. This occurred in discrete stress- and pathway-specific combinations, providing a framework for future defense-enhancing strategies.

Large Neck and Strong Ostium Inflow as the Potential Causes for Delayed Occlusion of Unruptured Sidewall Intracranial Aneurysms Treated by Flow Diverter

BACKGROUND AND PURPOSE

Flow diverter-induced hemodynamic change plays an important role in the mechanism of intracranial aneurysm occlusion. Our aim was to explore the relationship between aneurysm features and flow-diverter treatment of unruptured sidewall intracranial aneurysms.

MATERIALS AND METHODS

MR imaging, 4D phase-contrast, was prospectively performed before flow diverter implantation in each patient with unruptured intracranial aneurysm. Two postprocedure follow-ups were scheduled at 6 and 12 months. Responses were grouped according to whether the aneurysms were occluded or remnant. Preprocedural aneurysm geometries and ostium hemodynamics in 38 patients were compared between the 2 groups at 6 and 12 months. Receiver operating characteristic curve analyses were performed for significant geometric and hemodynamic continuous parameters.

RESULTS

After the 6-month assessment, 21 of 41 intracranial aneurysms were occluded, and 9 additional aneurysms were occluded at 12 months. Geometrically, the ostium maximum diameter was significantly larger in the remnant group at 6 and 12 months (both P < .001). Hemodynamically, the proximal inflow zone was more frequently observed in the remnant group at 6 months. Several preprocedural ostium hemodynamic parameters were significantly higher in the remnant group. As a prediction for occlusion, the areas under the curve of the ostium maximum diameter (for 6 and 12 months), systolic inflow rate ratio (for 6 months), and systolic inflow area (for 12 months) reached 0.843, 0.883, 0.855, and 0.860, respectively.

CONCLUSIONS

Intracranial aneurysms with a large ostium and strong ostium inflow may need a longer time for occlusion. Preprocedural 4D flow MR imaging can well illustrate ostium hemodynamics and characterize aneurysm treatment responses.

How Flow Reduction Influences the Intracranial Aneurysm Occlusion: A Prospective 4D Phase-Contrast MRI Study

BACKGROUND AND PURPOSE

Flow-diverter stents are widely used for the treatment of wide-neck intracranial aneurysms. Various parameters may influence intracranial aneurysm thrombosis, including the flow reduction induced by flow-diverter stent implantation, which is assumed to play a leading role. However, its actual impact remains unclear due to the lack of detailed intra-aneurysmal flow measurements. This study aimed to clarify this relationship by quantitatively measuring the intra-aneurysmal flow using 4D phase-contrast MR imaging.

MATERIALS AND METHODS

We acquired prospective pre- and post-stent implantation 4D phase-contrast MR imaging data of a consecutive series of 23 patients treated with flow-diverter stents. Velocity field data were combined with the intraprocedural 3D angiogram vessel geometries for precise intracranial aneurysm extraction and partial volume correction. Intra-aneurysmal hemodynamic modifications were compared with occlusion outcomes at 6 and 12 months.

RESULTS

The averaged velocities at systole were lower after flow-diverter stent implantation for all patients and ranged from 21.7 ± 7.1 cm/s before to 7.2 ± 2.9 cm/s after stent placement. The velocity reduction was more important for the group of patients with aneurysm thrombosis at 6 months (68.8%) and decreased gradually from 66.2% to 55% for 12-month thrombosis and no thrombosis, respectively (P = .08).

CONCLUSIONS

We propose an innovative approach to measure intracranial flow changes after flow-diverter stent implantation. We identified a trend between flow reduction and thrombosis outcome that brings a new insight into current understanding of the flow-diversion treatment response.

Jasmonate-Related MYC Transcription Factors Are Functionally Conserved in Marchantia polymorpha

The lipid-derived phytohormone jasmonoyl-isoleucine regulates plant immunity, growth and development in vascular plants by activating genome-wide transcriptional reprogramming. In Arabidopsis (Arabidopsis thaliana), this process is largely orchestrated by the master regulator MYC2 and related transcription factors (TFs). However, the TFs activating this pathway in basal plant lineages are currently unknown. We report the functional conservation of MYC-related TFs between the eudicot Arabidopsis and the liverwort Marchantia polymorpha, a plant belonging to an early diverging lineage of land plants. Phylogenetic analysis suggests that MYC function first appeared in charophycean algae and therefore predates the evolutionary appearance of any other jasmonate pathway component. M. polymorpha possesses two functionally interchangeable MYC genes, one in females and one in males. Similar to AtMYC2, MpMYCs showed nuclear localization, interaction with JASMONATE-ZIM-DOMAIN PROTEIN repressors, and regulation by light. Phenotypic and molecular characterization of loss- and gain-of-function mutants demonstrated that MpMYCs are necessary and sufficient for activating the jasmonate pathway in M. polymorpha, but unlike their Arabidopsis orthologs, do not regulate fertility. Therefore, despite 450 million years of independent evolution, MYCs are functionally conserved between bryophytes and eudicots. Genetic conservation in an early diverging lineage suggests that MYC function existed in the common ancestor of land plants and evolved from a preexisting MYC function in charophycean algae.

Molecular Interactions Between Plants and Insect Herbivores

Diverse molecular processes regulate the interactions between plants and insect herbivores. Here, we review genes and proteins that are involved in plant-herbivore interactions and discuss how their discovery has structured the current standard model of plant-herbivore interactions. Plants perceive damage-associated and, possibly, herbivore-associated molecular patterns via receptors that activate early signaling components such as Ca²⁺, reactive oxygen species, and MAP kinases. Specific defense reprogramming proceeds via signaling networks that include phytohormones, secondary metabolites, and transcription factors. Local and systemic regulation of toxins, defense proteins, physical barriers, and tolerance traits protect plants against herbivores. Herbivores counteract plant defenses through biochemical defense deactivation, effector-mediated suppression of defense signaling, and chemically controlled behavioral changes. The molecular basis of plant-herbivore interactions is now well established for model systems. Expanding molecular approaches to unexplored dimensions of plant-insect interactions should be a future priority.

The Arabidopsis Lectin Receptor Kinase LecRK-I.8 Is Involved in Insect Egg Perception

Plants induce defense responses after insect egg deposition, but very little is known about the perception mechanisms. In Arabidopsis thaliana, eggs of the specialist insect Pieris brassicae trigger accumulation of reactive oxygen species (ROS) and salicylic acid (SA), followed by induction of defense genes and localized necrosis. Here, the involvement of the clade I L-type lectin receptor kinase LecRK-I.8 in these responses was studied. Expression of LecRK-I.8 was upregulated at the site of P. brassicae oviposition and egg extract (EE) treatment. ROS, SA, cell death, and expression of PR1 were substantially reduced in the Arabidopsis knock-out mutant lecrk-I.8 after EE treatment. In addition, EE-induced systemic resistance against Pseudomonas syringae was abolished in lecrk-I.8. Expression of ten clade I homologs of LecRK-I.8 was also induced by EE treatment, but single mutants displayed only weak alteration of EE-induced PR1 expression. These results demonstrate that LecRK-I.8 is an early component of egg perception.

Ligand-receptor co-evolution shaped the jasmonate pathway in land plants

The phytohormone jasmonoyl-isoleucine (JA-Ile) regulates defense, growth and developmental responses in vascular plants. Bryophytes have conserved sequences for all JA-Ile signaling pathway components but lack JA-Ile. We show that, in spite of 450 million years of independent evolution, the JA-Ile receptor COI1 is functionally conserved between the bryophyte Marchantia polymorpha and the eudicot Arabidopsis thaliana but COI1 responds to different ligands in each species. We identified the ligand of Marchantia MpCOI1 as two isomeric forms of the JA-Ile precursor dinor-OPDA (dinor-cis-OPDA and dinor-iso-OPDA). We demonstrate that AtCOI1 functionally complements Mpcoi1 mutation and confers JA-Ile responsiveness and that a single-residue substitution in MpCOI1 is responsible for the evolutionary switch in ligand specificity. Our results identify the ancestral bioactive jasmonate and clarify its biosynthetic pathway, demonstrate the functional conservation of its signaling pathway, and show that JA-Ile and COI1 emergence in vascular plants required co-evolution of hormone biosynthetic complexity and receptor specificity.

The Cuticle Mutant eca2 Modifies Plant Defense Responses to Biotrophic and Necrotrophic Pathogens and Herbivory Insects

We isolated previously several Arabidopsis thaliana mutants with constitutive expression of the early microbe-associated molecular pattern-induced gene ATL2, named eca (expresión constitutiva de ATL2). Here, we further explored the interaction of eca mutants with pest and pathogens. Of all eca mutants, eca2 was more resistant to a fungal pathogen (Botrytis cinerea) and a bacterial pathogen (Pseudomonas syringae) as well as to a generalist herbivorous insect (Spodoptera littoralis). Permeability of the cuticle is increased in eca2; chemical characterization shows that eca2 has a significant reduction of both cuticular wax and cutin. Additionally, we determined that eca2 did not display a similar compensatory transcriptional response, compared with a previously characterized cuticular mutant, and that resistance to B. cinerea is mediated by the priming of the early and late induced defense responses, including salicylic acid- and jasmonic acid-induced genes. These results suggest that ECA2-dependent responses are involved in the nonhost defense mechanism against biotrophic and necrotrophic pathogens and against a generalist insect by modulation and priming of innate immunity and late defense responses. Making eca2 an interesting model to characterize the molecular basis for plant defenses against different biotic interactions and to study the initial events that take place in the cuticle surface of the aerial organs.

Plant-arthropod interactions: who is the winner?

Herbivorous arthropods have interacted with plants for millions of years. During feeding they release chemical cues that allow plants to detect the attack and mount an efficient defense response. A signaling cascade triggers the expression of hundreds of genes, which encode defensive proteins and enzymes for synthesis of toxic metabolites. This direct defense is often complemented by emission of volatiles that attract beneficial parasitoids. In return, arthropods have evolved strategies to interfere with plant defenses, either by producing effectors to inhibit detection and downstream signaling steps, or by adapting to their detrimental effect. In this review, we address the current knowledge on the molecular and chemical dialog between plants and herbivores, with an emphasis on co-evolutionary aspects.

An OPR3-independent pathway uses 4,5-didehydrojasmonate for jasmonate synthesis

Biosynthesis of the phytohormone jasmonoyl-isoleucine (JA-Ile) requires reduction of the JA precursor 12-oxo-phytodienoic acid (OPDA) by OPDA reductase 3 (OPR3). Previous analyses of the opr3-1 Arabidopsis mutant suggested an OPDA signaling role independent of JA-Ile and its receptor COI1; however, this hypothesis has been challenged because opr3-1 is a conditional allele not completely impaired in JA-Ile biosynthesis. To clarify the role of OPR3 and OPDA in JA-independent defenses, we isolated and characterized a loss-of-function opr3-3 allele. Strikingly, opr3-3 plants remained resistant to necrotrophic pathogens and insect feeding, and activated COI1-dependent JA-mediated gene expression. Analysis of OPDA derivatives identified 4,5-didehydro-JA in wounded wild-type and opr3-3 plants. OPR2 was found to reduce 4,5-didehydro-JA to JA, explaining the accumulation of JA-Ile and activation of JA-Ile-responses in opr3-3 mutants. Our results demonstrate that in the absence of OPR3, OPDA enters the β-oxidation pathway to produce 4,5-ddh-JA as a direct precursor of JA and JA-Ile, thus identifying an OPR3-independent pathway for JA biosynthesis.

Low number of fixed somatic mutations in a long-lived oak tree

Because plants do not possess a defined germline, deleterious somatic mutations can be passed to gametes, and a large number of cell divisions separating zygote from gamete formation may lead to many mutations in long-lived plants. We sequenced the genome of two terminal branches of a 234-year-old oak tree and found several fixed somatic single-nucleotide variants whose sequential appearance in the tree could be traced along nested sectors of younger branches. Our data suggest that stem cells of shoot meristems in trees are robustly protected from the accumulation of mutations.

Combined biotic stresses trigger similar transcriptomic responses but contrasting resistance against a chewing herbivore in Brassica nigra

BACKGROUND

In nature, plants are frequently exposed to simultaneous biotic stresses that activate distinct and often antagonistic defense signaling pathways. How plants integrate this information and whether they prioritize one stress over the other is not well understood.

RESULTS

We investigated the transcriptome signature of the wild annual crucifer, Brassica nigra, in response to eggs and caterpillars of Pieris brassicae butterflies, Brevicoryne brassicae aphids and the bacterial phytopathogen Xanthomonas campestris pv. raphani (Xcr). Pretreatment with egg extract, aphids, or Xcr had a weak impact on the subsequent transcriptome profile of plants challenged with caterpillars, suggesting that the second stress dominates the transcriptional response. Nevertheless, P. brassicae larval performance was strongly affected by egg extract or Xcr pretreatment and depended on the site where the initial stress was applied. Although egg extract and Xcr pretreatments inhibited insect-induced defense gene expression, suggesting salicylic acid (SA)/jasmonic acid (JA) pathway cross talk, this was not strictly correlated with larval performance.

CONCLUSION

These results emphasize the need to better integrate plant responses at different levels of biological organization and to consider localized effects in order to predict the consequence of multiple stresses on plant resistance.

Arabidopsis glucosinolates trigger a contrasting transcriptomic response in a generalist and a specialist herbivore

Phytophagous insects have to deal with toxic defense compounds from their host plants. Although it is known that insects have evolved genes and mechanisms to detoxify plant allochemicals, how specialist and generalist precisely respond to specific secondary metabolites at the molecular level is less understood. Here we studied the larval performance and transcriptome of the generalist moth Heliothis virescens and the specialist butterfly Pieris brassicae feeding on Arabidopsis thaliana genotypes with different glucosinolate (GS) levels. H. virescens larvae gained significantly more weight on the GS-deficient mutant quadGS compared to wild-type (Col-0) plants. On the contrary, P. brassicae was unaffected by the presence of GS and performed equally well on both genotypes. Strikingly, there was a considerable differential gene expression in H. virescens larvae feeding on Col-0 compared to quadGS. In contrast, compared to H. virescens, P. brassicae displayed a much-reduced transcriptional activation when fed on both plant genotypes. Transcripts coding for putative detoxification enzymes were significantly upregulated in H. virescens, along with digestive enzymes and transposable elements. These data provide an unprecedented view on transcriptional changes that are specifically activated by GS and illustrate differential molecular responses that are linked to adaptation to diet in lepidopteran herbivores.

Central Metabolic Responses to Ozone and Herbivory Affect Photosynthesis and Stomatal Closure

Plants have evolved adaptive mechanisms that allow them to tolerate a continuous range of abiotic and biotic stressors. Tropospheric ozone (O3), a global anthropogenic pollutant, directly affects living organisms and ecosystems, including plant-herbivore interactions. In this study, we investigate the stress responses of Brassica nigra (wild black mustard) exposed consecutively to O3 and the specialist herbivore Pieris brassicae Transcriptomics and metabolomics data were evaluated using multivariate, correlation, and network analyses for the O3 and herbivory responses. O3 stress symptoms resembled those of senescence and phosphate starvation, while a sequential shift from O3 to herbivory induced characteristic plant defense responses, including a decrease in central metabolism, induction of the jasmonic acid/ethylene pathways, and emission of volatiles. Omics network and pathway analyses predicted a link between glycerol and central energy metabolism that influences the osmotic stress response and stomatal closure. Further physiological measurements confirmed that while O3 stress inhibited photosynthesis and carbon assimilation, sequential herbivory counteracted the initial responses induced by O3, resulting in a phenotype similar to that observed after herbivory alone. This study clarifies the consequences of multiple stress interactions on a plant metabolic system and also illustrates how omics data can be integrated to generate new hypotheses in ecology and plant physiology.

Plant Immune Responses: Aphids Strike Back

To survive and complete their life cycle, herbivorous insects face the difficult challenge of coping with the arsenal of plant defences. A new study reports that aphids secrete evolutionarily conserved cytokines in their saliva to suppress host immune responses.

Arabidopsis MYC Transcription Factors Are the Target of Hormonal Salicylic Acid/Jasmonic Acid Cross Talk in Response to Pieris brassicae Egg Extract

Arabidopsis (Arabidopsis thaliana) plants recognize insect eggs and activate the salicylic acid (SA) pathway. As a consequence, expression of defense genes regulated by the jasmonic acid (JA) pathway is suppressed and larval performance is enhanced. Cross talk between defense signaling pathways is common in plant-pathogen interactions, but the molecular mechanism mediating this phenomenon is poorly understood. Here, we demonstrate that egg-induced SA/JA antagonism works independently of the APETALA2/ETHYLENE RESPONSE FACTOR (AP2/ERF) transcription factor ORA59, which controls the ERF branch of the JA pathway. In addition, treatment with egg extract did not enhance expression or stability of JASMONATE ZIM-domain transcriptional repressors, and SA/JA cross talk did not involve JASMONATE ASSOCIATED MYC2-LIKEs, which are negative regulators of the JA pathway. Investigating the stability of MYC2, MYC3, and MYC4, three basic helix-loop-helix transcription factors that additively control jasmonate-related defense responses, we found that egg extract treatment strongly diminished MYC protein levels in an SA-dependent manner. Furthermore, we identified WRKY75 as a novel and essential factor controlling SA/JA cross talk. These data indicate that insect eggs target the MYC branch of the JA pathway and uncover an unexpected modulation of SA/JA antagonism depending on the biological context in which the SA pathway is activated.

Trade-off between constitutive and inducible resistance against herbivores is only partially explained by gene expression and glucosinolate production

The hypothesis that constitutive and inducible plant resistance against herbivores should trade-off because they use the same resources and impose costs to plant fitness has been postulated for a long time. Negative correlations between modes of deployment of resistance and defences have been observed across and within species in common garden experiments. It was therefore tested whether that pattern of resistance across genotypes follows a similar variation in patterns of gene expression and chemical defence production. Using the genetically tractable model Arabidopsis thaliana and different modes of induction, including the generalist herbivore Spodoptera littoralis, the specialist herbivore Pieris brassicae, and jasmonate application, constitutive and inducibility of resistance was measured across seven A. thaliana accessions that were previously selected based on constitutive levels of defence gene expression. According to theory, it was found that modes of resistance traded-off among accessions, particularly against S. littoralis, in which accessions investing in high constitutive resistance did not increase it substantially after attack and vice-versa. Accordingly, the average expression of eight genes involved in glucosinolate production negatively predicted larval growth across the seven accessions. Glucosinolate production and genes related to defence induction on healthy and herbivore-damaged plants were measured next. Surprisingly, only a partial correlation between glucosinolate production, gene expression, and the herbivore resistance results was found. These results suggest that the defence outcome of plants against herbivores goes beyond individual molecules or genes but stands on a complex network of interactions.

Insect eggs induce a systemic acquired resistance in Arabidopsis

Although they constitute an inert stage of the insect's life, eggs trigger plant defences that lead to egg mortality or attraction of egg parasitoids. We recently found that salicylic acid (SA) accumulates in response to oviposition by the Large White butterfly Pieris brassicae, both in local and systemic leaves, and that plants activate a response that is similar to the recognition of pathogen-associated molecular patterns (PAMPs), which are involved in PAMP-triggered immunity (PTI). Here we discovered that natural oviposition by P. brassicae or treatment with egg extract inhibit growth of different Pseudomonas syringae strains in Arabidopsis through the activation of a systemic acquired resistance (SAR). This egg-induced SAR involves the metabolic SAR signal pipecolic acid, depends on ALD1 and FMO1, and is accompanied by a stronger induction of defence genes upon secondary infection. Although P. brassicae larvae showed a reduced performance when feeding on Pseudomonas syringae-infected plants, this effect was less pronounced when infected plants had been previously oviposited. Altogether, our results indicate that egg-induced SAR might have evolved as a strategy to prevent the detrimental effect of bacterial pathogens on feeding larvae.

Perception, signaling and molecular basis of oviposition-mediated plant responses

Eggs deposited on plants by herbivorous insects represent a threat as they develop into feeding larvae. Plants are not a passive substrate and have evolved sophisticated mechanisms to detect eggs and induce direct and indirect defenses. Recent years have seen exciting development in molecular aspects of egg-induced responses. Some egg-associated elicitors have been identified, and signaling pathways and egg-induced expression profiles are being uncovered. Depending on the mode of oviposition, both the jasmonic acid and salicylic acid pathways seem to play a role in the induction of defense responses. An emerging concept is that eggs are recognized like microbial pathogens and innate immune responses are triggered. In addition, some eggs contain elicitors that induce highly specific defenses in plants. Examples of egg-induced suppression of defense or, on the contrary, egg-induced resistance highlight the complexity of plant-egg interactions in an on-going arms race between herbivores and their hosts. A major challenge is to identify plant receptors for egg-associated elicitors, to assess the specificity of these elicitors and to identify molecular components that underlie various responses to oviposition.

Arabidopsis basic helix-loop-helix transcription factors MYC2, MYC3, and MYC4 regulate glucosinolate biosynthesis, insect performance, and feeding behavior

Arabidopsis thaliana plants fend off insect attack by constitutive and inducible production of toxic metabolites, such as glucosinolates (GSs). A triple mutant lacking MYC2, MYC3, and MYC4, three basic helix-loop-helix transcription factors that are known to additively control jasmonate-related defense responses, was shown to have a highly reduced expression of GS biosynthesis genes. The myc2 myc3 myc4 (myc234) triple mutant was almost completely devoid of GS and was extremely susceptible to the generalist herbivore Spodoptera littoralis. On the contrary, the specialist Pieris brassicae was unaffected by the presence of GS and preferred to feed on wild-type plants. In addition, lack of GS in myc234 drastically modified S. littoralis feeding behavior. Surprisingly, the expression of MYB factors known to regulate GS biosynthesis genes was not altered in myc234, suggesting that MYC2/MYC3/MYC4 are necessary for direct transcriptional activation of GS biosynthesis genes. To support this, chromatin immunoprecipitation analysis showed that MYC2 binds directly to the promoter of several GS biosynthesis genes in vivo. Furthermore, yeast two-hybrid and pull-down experiments indicated that MYC2/MYC3/MYC4 interact directly with GS-related MYBs. This specific MYC-MYB interaction plays a crucial role in the regulation of defense secondary metabolite production and underlines the importance of GS in shaping plant interactions with adapted and nonadapted herbivores.