Onset Of Programmed Cell Death Research Articles

Grapevine Rpv3-, Rpv10- and Rpv12-mediated defense responses against Plasmopara viticola and the impact of their deployment on fungicide use in viticulture

BackgroundThe high susceptibility of European grapevine cultivars (Vitis vinifera) to downy mildew (Plasmopara viticola) leads to the intensive use of fungicides in viticulture. To reduce this input, breeding programs have introgressed resistance loci from wild Vitis species into V. vinifera, resulting in new fungus-resistant grapevine cultivars (FRC). However, little is known about how these different resistance loci confer resistance and what the potential reduction in fungicide applications are likely to be if these FRCs are deployed. To ensure a durable and sustainable resistance management and breeding, detailed knowledge about the different defense mechanisms mediated by the respective Rpv (Resistance to P. viticola) resistance loci is essential.ResultsA comparison of the resistance mechanisms mediated by the Rpv3–1, Rpv10 and/or Rpv12-loci revealed an early onset of programmed cell death (PCD) at 8 hours post infection (hpi) in Rpv12-cultivars and 12 hpi in Rpv10-cultivars, whereas cell death was delayed in Rpv3-cultivars and was not observed until 28 hpi. These temporal differences correlated with an increase in the trans-resveratrol level and the formation of hydrogen peroxide shortly before onset of PCD. The differences in timing of onset of Rpv-loci specific defense reactions following downy mildew infection could be responsible for the observed differences in hyphal growth, sporulation and cultivar-specific susceptibility to this pathogen in the vineyard. Hereby, Rpv3- and Rpv12/Rpv3-cultivars showed a potential for a significant reduction of fungicide applications, depending on the annual P. viticola infection pressure and the Rpv-loci. Furthermore, we report on the discovery of a new P. viticola isolate that is able to overcome both Rpv3- and Rpv12-mediated resistance.ConclusionThis study reveals that differences in the timing of the defense reaction mediated by the Rpv3-, Rpv10- and Rpv12-loci, result in different degrees of natural resistance to downy mildew in field. Vineyard trials demonstrate that Rpv12/Rpv3- and Rpv3-cultivars are a powerful tool to reduce the dependence of grape production on fungicide applications. Furthermore, this study indicates the importance of sustainable breeding and plant protection strategies based on resistant grapevine cultivars to reduce the risk of new P. viticola isolates that are able to overcome the respective resistance mechanism.

Calcium Signaling in Plant Programmed Cell Death.

Programmed cell death (PCD) is a process intended for the maintenance of cellular homeostasis by eliminating old, damaged, or unwanted cells. In plants, PCD takes place during developmental processes and in response to biotic and abiotic stresses. In contrast to the field of animal studies, PCD is not well understood in plants. Calcium (Ca2+) is a universal cell signaling entity and regulates numerous physiological activities across all the kingdoms of life. The cytosolic increase in Ca2+ is a prerequisite for the induction of PCD in plants. Although over the past years, we have witnessed significant progress in understanding the role of Ca2+ in the regulation of PCD, it is still unclear how the upstream stress perception leads to the Ca2+ elevation and how the signal is further propagated to result in the onset of PCD. In this review article, we discuss recent advancements in the field, and compare the role of Ca2+ signaling in PCD in biotic and abiotic stresses. Moreover, we discuss the upstream and downstream components of Ca2+ signaling and its crosstalk with other signaling pathways in PCD. The review is expected to provide new insights into the role of Ca2+ signaling in PCD and to identify gaps for future research efforts.

Polycomb Repressive Complex 2 and KRYPTONITE regulate pathogen-induced programmed cell death in Arabidopsis.

The Polycomb Repressive Complex 2 (PRC2) is well-known for its role in controlling developmental transitions by suppressing the premature expression of key developmental regulators. Previous work revealed that PRC2 also controls the onset of senescence, a form of developmental programmed cell death (PCD) in plants. Whether the induction of PCD in response to stress is similarly suppressed by the PRC2 remained largely unknown. In this study, we explored whether PCD triggered in response to immunity- and disease-promoting pathogen effectors is associated with changes in the distribution of the PRC2-mediated histone H3 lysine 27 trimethylation (H3K27me3) modification in Arabidopsis thaliana. We furthermore tested the distribution of the heterochromatic histone mark H3K9me2, which is established, to a large extent, by the H3K9 methyltransferase KRYPTONITE, and occupies chromatin regions generally not targeted by PRC2. We report that effector-induced PCD caused major changes in the distribution of both repressive epigenetic modifications and that both modifications have a regulatory role and impact on the onset of PCD during pathogen infection. Our work highlights that the transition to pathogen-induced PCD is epigenetically controlled, revealing striking similarities to developmental PCD.

Using proteomic analysis to find the proteins involved in resistance against Sclerotinia sclerotiorum in adult Brassica napus

Sclerotinia disease, caused by Sclerotinia sclerotiorum, is one of the most serious plant diseases in China. Research on the mechanism of disease resistance to S. sclerotiorum will help solve control problems. In this study, near-isogenic lines were first used in combination with the proteomic technique. A comparison of protein expression profiles in a susceptible line with those in a resistant line during the interaction of adult Brassica napus with S. sclerotiorum resulted in the identification of 20 important proteins related to disease resistance. Those proteins were then determined to be involved in various functions, including pathogen resistance, antioxidation, and transcription regulation. Our finding showed that some proteins involved in defence—a glycine rich protein (GRP); a trypsin inhibitor protein (TIP); two heat shock proteins (HSPs); and a thiol methyltransferase (TMT)—were upregulated or expressed specially in the resistant B. napus lines. These proteins contribute to ROS (reactive oxygen species) elimination and pathogen-defence in the resistant line, which would help the host defend itself against S. sclerotiorum. As a consequence, the onset of PCD (programmed cell death) was delayed, and the spread of S. sclerotiorum was slowed in the resistant line. Presented results underline the role of specific proteins in the disease process. By building on these results, future research may help determine the genes that are important in conveying resistance to S. sclerotiorum in B. napus.

TGBp3 triggers the unfolded protein response and SKP1‐dependent programmed cell death

The Potato virus X (PVX) triple gene block protein 3 (TGBp3), an 8-kDa membrane binding protein, aids virus movement and induces the unfolded protein response (UPR) during PVX infection. TGBp3 was expressed from the Tobacco mosaic virus (TMV) genome (TMV-p3), and we noted the up-regulation of SKP1 and several endoplasmic reticulum (ER)-resident chaperones, including the ER luminal binding protein (BiP), protein disulphide isomerase (PDI), calreticulin (CRT) and calmodulin (CAM). Local lesions were seen on leaves inoculated with TMV-p3, but not TMV or PVX. Such lesions were the result of TGBp3-elicited programmed cell death (PCD), as shown by an increase in reactive oxygen species, DNA fragmentation and induction of SKP1 expression. UPR-related gene expression occurred within 8 h of TMV-p3 inoculation and declined before the onset of PCD. TGBp3-mediated cell death was suppressed in plants that overexpressed BiP, indicating that UPR induction by TGBp3 is a pro-survival mechanism. Anti-apoptotic genes Bcl-xl, CED-9 and Op-IAP were expressed in transgenic plants and suppressed N gene-mediated resistance to TMV, but failed to alleviate TGBp3-induced PCD. However, TGBp3-mediated cell death was reduced in SKP1-silenced Nicotiana benthamiana plants. The combined data suggest that TGBp3 triggers the UPR and elicits PCD in plants.

Short-term salinity stress in tobacco plants leads to the onset of animal-like PCD hallmarks in planta in contrast to long-term stress

Recent results have identified mitochondria as centers of stress-induced generation of reactive oxygen species in plants. Depolarization of plant mitochondrial membrane during stress results the release of programmed cell death (PCD)-inducing factors in the cytosol in a fashion similar to the onset of animal-like PCD. Herein, we report significant similarities of animal-like PCD and salinity stress-induced plant PCD. Short-term salinity stress (3 h) led to depolarization of the mitochondrial membrane, release of cytochrome c (CYT-c), which was visualized using a contemporary molecular technique, activation of caspase-3 type proteases and the onset of PCD in wild type tobacco plants, Nicotiana tabacum cv. Petit Havana. However, PCD was not manifested during long-term salinity stress (24 h). Interestingly long-term salinity stress led to necrotic-like features, which were accompanied by collapse of respiration, reduction of key components of the respiratory chain, such as CYT-c and alternative oxidase, ATP depletion and high proteolytic activity. The results suggest that salinity stress of tobacco plants in planta leads to the onset of animal-like PCD only during the early stages post-stress, while long-term stress leads to necrotic-like features.

Up- and downregulated genes in muscles that undergo developmentally programmed cell death in the insect Manduca sexta

This study was designed to investigate changes in gene expression associated with stage-specific programmed cell death (PCD) in intersegmental muscles (ISMs) of the moth, Manduca sexta. The technique of differential display reverse transcription PCR was applied to compare mRNA levels before and after the onset of PCD in ISMs. Expression of E75 B transcription factor was repressed while another factor, βFTZ-F1, stayed at a very low level. However, gene coding for a translation-initiation factor ( eIF1A) was upregulated. Expression of these genes had not been previously reported to be altered in dying ISMs. An ecdysteroid agonist, RH-5849, that prevented PCD in ISMs also blocked these changes.

Salt stress-induced programmed cell death via Ca2+-mediated mitochondrial permeability transition in tobacco protoplasts

The change in cytosolic free concentration of calcium ([Ca2+]cyt) plays a key role in regulating apoptosis in animal cells. In our experiment, we tried to investigate the function of Ca2+ in programmed cell death (PCD) in tobacco (Nicotiana tobacum, cultivar BY-2) protoplasts induced by salt stress. An obvious increase in [Ca2+]cyt was observed a few minutes after treatment and the onset of a decrease in mitochondrial membrane potential (ΔΨm) was also observed before the appearance of PCD, pre-treatment of protoplasts with EGTA or LaCl3 effectively retarded the increase in [Ca2+]cyt, which was concomitant with the decrease in the percentage of cell death and higher ΔΨm, pre-treatment with cyclosporine A (CsA) also effectively retarded the increase in [Ca2+]cyt, the decrease in ΔΨm and the onset of PCD. All these results suggest that Ca2+ is a necessary element in regulating PCD and the increase in [Ca2+]cyt and the opening of mitochondrial permeability transition pore (MPTP) could promote each other in regulating PCD in tobacco protoplasts induced by salt stress.

Hormonal Control of “Tissue” Transglutaminase Induction during Programmed Cell Death in Frog Liver

In this study, we show that sex hormones (testosterone, estradiol, and progesterone) act as physiological modulators of programmed cell death (PCD) during the frog liver involution observed postvitellogenesis. PCD in parenchymal cells is paralleled by the specific induction of the “tissue” transglutaminase (tTG) gene. tTG protein specifically accumulates in hepatocytes showing the morphological features of apoptosis. The hormone-dependent increase of both PCD and tTG was reproduced in ovariectomized frogs. Treatment of castrated animals with testosterone, estradiol, and progesterone inhibited the induction of both tTG and PCD, thus indicating thatin vivothe drop in the circulating sex hormone is the signal favoring the involution phase of the maternal frog liver after mating. Although an affinity-purified polyclonal antibody raised against mammalian transglutaminase reacts in frog liver with a 55- to 60-kDa protein, concomitant with the onset of PCD, tTG cleavage products were detected, suggesting a proteolytic processing of the enzyme protein. These results represent the first evidence indicating that the physiological involution occurring postvitellogenesis of frog liver takes place by programmed cell death and that this, together with the concomitant induction of tTG gene expression, is regulated by sex hormones.

Programmed cell death is a universal feature of embryonic and postnatal neuroproliferative regions throughout the central nervous system.

During central nervous system (CNS) development, programmed cell death (PCD) has been viewed traditionally as a fate reserved for differentiating neurons that are in the process of making synaptic connections. Recent studies in the embryonic cerebral cortex (Blaschke et al. [1996] Development 122:1165-1174), however, have shown that many neuroblasts in the proliferative ventricular zone undergo PCD as well and that this likely represents a novel form distinct from that found in regions of postmitotic neurons. To determine the commonality of this form of PCD throughout the CNS, the prevalence of dying cells identified by in situ end labeling plus (ISEL +; Blaschke et al. [1996]) was determined within populations of proliferating neuroblasts that were identified by rapid bromodeoxyuridine incorporation. Based on this approach, dying cells were observed to be a common feature of all proliferative neuroblast populations examined. In addition, when ISEL+ was combined with in situ hybridization for postmitotic neural gene-1 (png-1; Weiner and Chun [1997] J. Comp. Neurol. 381:130-142), which identifies newly postmitotic neurons, a positive correlation was found between the start of differentiation and the onset of PCD. These data indicate that PCD in neuroblast proliferative zones is a universal feature of nervous system development. Moreover, cell death represents a prominent cell fate that may be linked to mechanisms of differentiation.