Abiotic stress induces apoptotic-like features in tobacco that is inhibited by expression of human Bcl-2

ROS generated from biotic stress: Effects on plants and alleviation by endophytic microbes

Aerobic living is thought to generate reactive oxygen species (ROS), which are an inevitable chemical component. They are produced exclusively in cellular compartments in aerobic metabolism involving significant energy transfer and are regarded as by-products. ROS have a significant role in plant response to pathogenic stress, but the pattern varies between necrotrophs and biotrophs. A fine-tuned systemic induction system is involved in ROS-mediated disease development in plants. In regulated concentrations, ROS act as a signaling molecule and activate different pathways to suppress the pathogens. However, an excess of these ROS is deleterious to the plant system. Along with altering cell structure, ROS cause a variety of physiological reactions in plants that lower plant yield. ROS also degrade proteins, enzymes, nucleic acids, and other substances. Plants have their own mechanisms to overcome excess ROS and maintain homeostasis. Microbes, especially endophytes, have been reported to maintain ROS homeostasis in both biotic and abiotic stresses by multiple mechanisms. Endophytes themselves produce antioxidant compounds and also induce host plant machinery to supplement ROS scavenging. The structured reviews on how endophytes play a role in ROS homeostasis under biotic stress were very meager, so an attempt was made to compile the recent developments in ROS homeostasis using endophytes. This review deals with ROS production, mechanisms involved in ROS signaling, host plant mechanisms in alleviating oxidative stress, and the roles of endophytes in maintaining ROS homeostasis under biotic stress.

Vacuolar Processing Enzymes Modulating Susceptibility Response to Fusarium oxysporum f. sp. cubense Tropical Race 4 Infections in Banana

Fusarium oxysporum f. sp. cubense tropical race 4 (FocTR4) is a destructive necrotrophic fungal pathogen afflicting global banana production. Infection process involves the activation of programmed cell death (PCD). In this study, seven Musa acuminata vacuolar processing enzyme (MaVPE1-MaVPE7) genes associated with PCD were successfully identified. Phylogenetic analysis and tissue-specific expression categorized these MaVPEs into the seed and vegetative types. FocTR4 infection induced the majority of MaVPE expressions in the susceptible cultivar "Berangan" as compared to the resistant cultivar "Jari Buaya." Consistently, upon FocTR4 infection, high caspase-1 activity was detected in the susceptible cultivar, while low level of caspase-1 activity was recorded in the resistant cultivar. Furthermore, inhibition of MaVPE activities via caspase-1 inhibitor in the susceptible cultivar reduced tonoplast rupture, decreased lesion formation, and enhanced stress tolerance against FocTR4 infection. Additionally, the Arabidopsis VPE-null mutant exhibited higher tolerance to FocTR4 infection, indicated by reduced sporulation rate, low levels of H₂O₂ content, and high levels of cell viability. Comparative proteomic profiling analysis revealed increase in the abundance of cysteine proteinase in the inoculated susceptible cultivar, as opposed to cysteine proteinase inhibitors in the resistant cultivar. In conclusion, the increase in vacuolar processing enzyme (VPE)-mediated PCD played a crucial role in modulating susceptibility response during compatible interaction, which facilitated FocTR4 colonization in the host.

Apoptosis is not conserved in plants as revealed by critical examination of a model for plant apoptosis-like cell death

BACKGROUND

Animals and plants diverged over one billion years ago and evolved unique mechanisms for many cellular processes, including cell death. One of the most well-studied cell death programmes in animals, apoptosis, involves gradual cell dismantling and engulfment of cellular fragments, apoptotic bodies, through phagocytosis. However, rigid cell walls prevent plant cell fragmentation and thus apoptosis is not applicable for executing cell death in plants. Furthermore, plants are devoid of the key components of apoptotic machinery, including phagocytosis as well as caspases and Bcl-2 family proteins. Nevertheless, the concept of plant "apoptosis-like programmed cell death" (AL-PCD) is widespread. This is largely due to superficial morphological resemblances between plant cell death and apoptosis, and in particular between protoplast shrinkage in plant cells killed by various stimuli and animal cell volume decrease preceding fragmentation into apoptotic bodies.

RESULTS

Here, we provide a comprehensive spatio-temporal analysis of cytological and biochemical events occurring in plant cells subjected to heat shock at 40-55 °C and 85 °C, the experimental conditions typically used to trigger AL-PCD and necrotic cell death, respectively. We show that cell death under both conditions was not accompanied by membrane blebbing or formation of apoptotic bodies, as would be expected during apoptosis. Instead, we observed instant and irreversible permeabilization of the plasma membrane and ATP depletion. These processes did not depend on mitochondrial functionality or the presence of Ca2+ and could not be prevented by an inhibitor of ferroptosis. We further reveal that the lack of protoplast shrinkage at 85 °C, the only striking morphological difference between cell deaths induced by 40-55 °C or 85 °C heat shock, is a consequence of the fixative effect of the high temperature on intracellular contents.

CONCLUSIONS

We conclude that heat shock-induced cell death is an energy-independent process best matching definition of necrosis. Although the initial steps of this necrotic cell death could be genetically regulated, classifying it as apoptosis or AL-PCD is a terminological misnomer. Our work supports the viewpoint that apoptosis is not conserved across animal and plant kingdoms and demonstrates the importance of focusing on plant-specific aspects of cell death pathways.

Centrality of BAGs in Plant PCD, Stress Responses, and Host Defense

Programmed cell death (PCD) is a genetically regulated process for the selective demise of unwanted and damaged cells. Although our understanding of plant PCD pathways has advanced significantly, doubts remain on the extent of conservation of animal apoptosis in plants. At least at the primary sequence level, plants do not encode the regulators of animal apoptosis. Structural analyses have enabled the identification of the B cell lymphoma 2 (Bcl-2)-associated athanogene (BAG) family of co-chaperones in plants. This discovery suggests that some aspects of animal PCD are conserved in plants, while the varied subcellular localization of plant BAGs indicates that they may have evolved distinct functions. Here we review plant BAG proteins, with an emphasis on their roles in the regulation of plant PCD.

Induction of Ced9 mediated anti-apoptosis in commercial banana cultivar Rasthali for stable resistance against Fusarium wilt

Anti-apoptotic gene Ced-9 enhanced resistance against Fusarium oxysporum f. sp. cubense (Foc) in the susceptible banana cultivar Rasthali by arresting tissue necrosis. The embryogenic cell suspension of banana cultivar Rasthali was stably transformed with Ced-9 gene and transformed lines were regenerated independently. The putative transgenic lines were analyzed with PCR using gene primers and further subjected to Southern blot to estimate copy number. The root-challenge bioassay with Foc showed 17-51% Vascular Discoloration Index in independent transformants compared to untransformed banana cv Rasthali (98% VDI). Four transgenic events showed a higher level of resistance over a period of 6 months. Overcoming tissue necrosis is the most ideal method to avoid Fusarium multiplication and spread in banana. Oxidative stress-induced cell necrosis is prevented by the activation of antiapoptotic pathways by Ced-9 and is proving to be an effective method to control this dreaded disease. This is the first report from India on the generation of transgenic banana cultivar Rasthali expressing antiapoptotic Ced-9 gene for resistance to Fusarium wilt.

BAKing up to Survive a Battle: Functional Dynamics of BAK1 in Plant Programmed Cell Death

In plants, programmed cell death (PCD) has diverse, essential roles in vegetative and reproductive development, and in the responses to abiotic and biotic stresses. Despite the rapid progress in understanding the occurrence and functions of the diverse forms of PCD in plants, the signaling components and molecular mechanisms underlying the core PCD machinery remain a mystery. The roles of BAK1 (BRASSINOSTEROID INSENSITIVE 1-associated receptor kinase 1), an essential co-receptor of multiple receptor complexes, in the regulation of immunity and development- and defense-related PCD have been well characterized. However, the ways in which BAK1 functions in mediating PCD need to be further explored. In this review, different forms of PCD in both plants and mammals are discussed. Moreover, we mainly summarize recent advances in elucidating the functions and possible mechanisms of BAK1 in controlling diverse forms of PCD. We also highlight the involvement of post-translational modifications (PTMs) of multiple signaling component proteins in BAK1-mediated PCD.

Disassembly of dying cells in diverse organisms

Programmed cell death (PCD) is a conserved phenomenon in multicellular organisms required to maintain homeostasis. Among the regulated cell death pathways, apoptosis is a well-described form of PCD in mammalian cells. One of the characteristic features of apoptosis is the change in cellular morphology, often leading to the fragmentation of the cell into smaller membrane-bound vesicles through a process called apoptotic cell disassembly. Interestingly, some of these morphological changes and cell disassembly are also noted in cells of other organisms including plants, fungi and protists while undergoing 'apoptosis-like PCD'. This review will describe morphologic features leading to apoptotic cell disassembly, as well as its regulation and function in mammalian cells. The occurrence of cell disassembly during cell death in other organisms namely zebrafish, fly and worm, as well as in other eukaryotic cells will also be discussed.

Reassessing apoptosis in plants

Cell death can be driven by a genetically programmed signalling pathway known as programmed cell death (PCD). In plants, PCD occurs during development as well as in response to environmental and biotic stimuli. Our understanding of PCD regulation in plants has advanced significantly over the past two decades; however, the molecular machinery responsible for driving the system remains elusive. Thus, whether conserved PCD regulatory mechanisms include plant apoptosis remains enigmatic. Animal apoptotic regulators, including Bcl-2 family members, have not been identified in plants but expression of such regulators can trigger or suppress plant PCD. Moreover, plants exhibit nearly all of the biochemical and morphological features of apoptosis. One difference between plant and animal PCD is the absence of phagocytosis in plants. Evidence is emerging that the vacuole may be key to removal of unwanted plant cells, and may carry out functions that are analogous to animal phagocytosis. Here, we provide context for the argument that apoptotic-like cell death occurs in plants.

Overexpression of human peroxisomal enoyl-CoA delta isomerase2 HsPECI2, an ortholog of bamboo expressed during gregarious flowering alters salinity stress responses and polar lipid content in tobacco

Peroxisomal enoyl-CoA delta isomerase2 (PECI2) is one of the key enzymes that has critical role in lipid metabolism and plant development during salt stress. Seven out of ten tobacco plants overexpressing human PECI2 (HsPECI2) with PTS1-sequence showed hypersensitivity to salt. Under salt-stress, T2 transformed plants (HsPECI2) displayed reduced primary root, delayed shoot-growth, and visibly smaller rosette leaves turning pale yellow as compared to the pKYLX71 vector control plant. Also, we found altered reactive oxygen species (ROS) levels and reduced catalase activity in 100mM sodium chloride (NaCl) treated HsPECI2 transformed plant compared with the pKYLX71 counterpart. ESI-MS/MS data showed that the polar lipids were differentially modulated upon salt treatment in HsPECI2 transformed and pKYLX71 plants as compared with the respective untreated counterpart. Notably, the levels of monogalactosyldiacylglycerol and phosphatidic acid varied significantly, whereas phosphatidylcholine, phosphatidylserine and digalactosyldiacylglycerol contents were moderately upregulated. In parallel, abscisic acid (ABA) responsiveness assay confirmed insensitivity of HsPECI2 transformed plant towards ABA. Overall our data proclaim that HsPECI2 play multifunctional role in normal development and response to salinity stress apart from its primary role in β-oxidation.

Bcl-2△21 and Ac-DEVD-CHO Inhibit Death of Wheat Microspores

Microspore cell death and low green plant production efficiency are an integral obstacle in the development of doubled haploid production in wheat. The aim of the current study was to determine the effect of anti-apoptotic recombinant human B-cell lymphoma-2 (Bcl-2△21) and caspase-3-inhibitor (Ac-DEVD-CHO) in microspore cell death in bread wheat cultivars AC Fielder and AC Andrew. Induction medium containing Bcl-2△21 and Ac-DEVD-CHO yielded a significantly higher number of viable microspores, embryo-like structures and total green plants in wheat cultivars AC Fielder and AC Andrew. Total peroxidase activity was lower in Bcl-2△21 treated microspore cultures at 96 h of treatment compared to control and Ac-DEVD-CHO. Electron paramagnetic resonance study of total microspore protein showed a different scavenging activity for Bcl-2△21 and Ac-DEVD-CHO. Bcl-2△21 scavenged approximately 50% hydroxyl radical (HO^•) formed, whereas Ac-DEVD-CHO scavenged approximately 20% of HO^•. Conversely, reduced caspase-3-like activities were detected in the presence of Bcl-2△21 and Ac-DEVD-CHO, supporting the involvement of Bcl-2△21 and Ac-DEVD-CHO in increasing microspore viability by reducing oxidative stress and caspase-3-like activity. Our results indicate that Bcl-2△21 and Ac-DEVD-CHO protects cells from cell death following different pathways. Bcl-2△21 prevents cell damage by detoxifying HO^• and suppressing caspase-3-like activity, while Ac-DEVD-CHO inhibits the cell death pathways by modulating caspase-like activity.

Development of salinity tolerance in rice by constitutive-overexpression of genes involved in the regulation of programmed cell death

Environmental factors contribute to over 70% of crop yield losses worldwide. Of these drought and salinity are the most significant causes of crop yield reduction. Rice is an important staple crop that feeds more than half of the world's population. However among the agronomically important cereals rice is the most sensitive to salinity. In the present study we show that exogenous expression of anti-apoptotic genes from diverse origins, AtBAG4 (Arabidopsis), Hsp70 (Citrus tristeza virus) and p35 (Baculovirus), significantly improves salinity tolerance in rice at the whole plant level. Physiological, biochemical and agronomical analyses of transgenic rice expressing each of the anti-apoptotic genes subjected to salinity treatment demonstrated traits associated with tolerant varieties including, improved photosynthesis, membrane integrity, ion and ROS maintenance systems, growth rate, and yield components. Moreover, FTIR analysis showed that the chemical composition of salinity-treated transgenic plants is reminiscent of non-treated, unstressed controls. In contrast, wild type and vector control plants displayed hallmark features of stress, including pectin degradation upon subjection to salinity treatment. Interestingly, despite their diverse origins, transgenic plants expressing the anti-apoptotic genes assessed in this study displayed similar physiological and biochemical characteristics during salinity treatment thus providing further evidence that cell death pathways are conserved across broad evolutionary kingdoms. Our results reveal that anti-apoptotic genes facilitate maintenance of metabolic activity at the whole plant level to create favorable conditions for cellular survival. It is these conditions that are crucial and conducive to the plants ability to tolerate/adapt to extreme environments.

Novel compounds that enhance Agrobacterium-mediated plant transformation by mitigating oxidative stress

KEY MESSAGE

Agrobacterium tumefaciens caused tissue browning leading to subsequent cell death in plant transformation and novel anti-oxidative compounds enhanced Agrobacterium -mediated plant transformation by mitigating oxidative stress. Browning and death of cells transformed with Agrobacterium tumefaciens is a long-standing and high impact problem in plant transformation and the agricultural biotechnology industry, severely limiting the production of transgenic plants. Using our tomato cv. MicroTom transformation system, we demonstrated that Agrobacterium caused tissue browning (TB) leading to subsequent cell death by our correlation study. Without an antioxidant (lipoic acid, LA) TB was severe and associated with high levels of GUS transient expression and low stable transformation frequency (STF). LA addition shifted the curve in that most TB was intermediate and associated with the highest levels of GUS transient expression and STF. We evaluated 18 novel anti-oxidative compounds for their potential to enhance Agrobacterium-mediated transformation, by screening for TB reduction and monitoring GUS transient expression. Promising compounds were further evaluated for their effect on MicroTom and soybean STF. Among twelve non-antioxidant compounds, seven and five significantly (P < 0.05) reduced TB and increased STF, respectively. Among six antioxidants four of them significantly reduced TB and five of them significantly increased STF. The most efficient compound found to increase STF was melatonin (MEL, an antioxidant). Optimal concentrations and stages to use MEL in transformation were determined, and Southern blot analysis showed that T-DNA integration was not affected by MEL. The ability of diverse compounds with different anti-oxidative mechanisms can reduce Agrobacterium-mediated TB and increase STF, strongly supporting that oxidative stress is an important limiting factor in Agrobacterium-mediated transformation and the limiting factor can be controlled by these compounds at different levels.

Progress in genetic engineering of peanut (Arachis hypogaea L.)--a review

Peanut (Arachis hypogaea L.) is a major species of the family, Leguminosae, and economically important not only for vegetable oil but as a source of proteins, minerals and vitamins. It is widely grown in the semi-arid tropics and plays a role in the world agricultural economy. Peanut production and productivity is constrained by several biotic (insect pests and diseases) and abiotic (drought, salinity, water logging and temperature aberrations) stresses, as a result of which crop experiences serious economic losses. Genetic engineering techniques such as Agrobacterium tumefaciens and DNA-bombardment-mediated transformation are used as powerful tools to complement conventional breeding and expedite peanut improvement by the introduction of agronomically useful traits in high-yield background. Resistance to several fungal, virus and insect pest have been achieved through variety of approaches ranging from gene coding for cell wall component, pathogenesis-related proteins, oxalate oxidase, bacterial chloroperoxidase, coat proteins, RNA interference, crystal proteins etc. To develop transgenic plants withstanding major abiotic stresses, genes coding transcription factors for drought and salinity, cytokinin biosynthesis, nucleic acid processing, ion antiporter and human antiapoptotic have been used. Moreover, peanut has also been used in vaccine production for the control of several animal diseases. In addition to above, this study also presents a comprehensive account on the influence of some important factors on peanut genetic engineering. Future research thrusts not only suggest the use of different approaches for higher expression of transgene(s) but also provide a way forward for the improvement of crops.

Physiological basis of salt stress tolerance in rice expressing the antiapoptotic gene SfIAP

Programmed cell death-associated genes, especially antiapoptosis-related genes have been reported to confer tolerance to a wide range of biotic and abiotic stresses in dicotyledonous plants such as tobacco (Nicotiana tabacum L.) and tomato (Solanum lycopersicum L.). This is the first time the antiapoptotic gene SfIAP was transformed into a monocotyledonous representative: rice (Oryza sativa L.). Transgenic rice strains expressing SfIAP were generated by the Agrobacterium-mediated transformation method and rice embryogenic calli, and assessed for their ability to confer tolerance to salt stress at both the seedling and reproductive stages using a combination of molecular, agronomical, physiological and biochemical techniques. The results show that plants expressing SfIAP have higher salt tolerance levels in comparison to the wild-type and vector controls. By preventing cell death at the onset of salt stress and maintaining the cell membrane's integrity, SfIAP transgenic rice plants can retain plant water status, ion homeostasis, photosynthetic efficiency and growth to combat salinity successfully.

Bcl-2 suppresses activation of VPEs by inhibiting cytosolic Ca²⁺ level with elevated K⁺ efflux in NaCl-induced PCD in rice

Bcl-2 is one of the most important antiapoptotic members in mammals and prevents many forms of apoptosis in a variety of cell types. Our previous study revealed that overexpression of Bcl-2 significantly suppressed H2O2/NaCl-induced programmed cell death via inhibiting the transcriptional activation of OsVPE2 and OsVPE3 in transgenic rice. However, Ca(2+) and K(+) homeostasis of this process remains largely unknown. In the present study, we investigate whether nonselective cation channels (NSCC) blockers affect Bcl-2 function in rice under salt stress and how Bcl-2 affects ion homeostasis in salt stress-induced PCD. The results showed that overexpression of Bcl-2 significantly decreased transient elevations in the cytosolic Ca(2+) levels, inhibited NaCl-induced K(+) efflux but not H(+) efflux across the plasma membrane, and further suppressed the expression levels of OsVPE2 and OsVPE3, leading to the inhibition of salt-induced PCD and increase of tolerance to salt stress in transgenic rice. During the NaCl-induced PCD, the effects of a NSCC blocker La(3+) on ion homeostasis and VPEs expression in wild-type were similar to the effects of Bcl-2 overexpression in transgenic line. However, a synergistic effect of Bcl-2 and La(3+) was not obviously detectable. Our results suggested that Bcl-2 played an important role in suppression of NaCl-induced PCD by disruption of ion homeostasis, providing an insight into the mechanistic study of plant VPEs, cytosolic Ca(2+) level and K(+) efflux.

Centrality of host cell death in plant-microbe interactions

Programmed cell death (PCD) is essential for proper growth, development, and cellular homeostasis in all eukaryotes. The regulation of PCD is of central importance in plant-microbe interactions; notably, PCD and features associated with PCD are observed in many host resistance responses. Conversely, pathogen induction of inappropriate cell death in the host results in a susceptible phenotype and disease. Thus, the party in control of PCD has a distinct advantage in these battles. PCD processes appear to be of ancient origin, as indicated by the fact that many features of cell death strategy are conserved between animals and plants; however, some of the details of death execution differ. Mammalian core PCD genes, such as caspases, are not present in plant genomes. Similarly, pro- and antiapoptotic mammalian regulatory elements are absent in plants, but, remarkably, when expressed in plants, successfully impact plant PCD. Thus, subtle structural similarities independent of sequence homology appear to sustain operational equivalence. The vacuole is emerging as a key organelle in the modulation of plant PCD. Under different signals for cell death, the vacuole either fuses with the plasmalemma membrane or disintegrates. Moreover, the vacuole appears to play a key role in autophagy; evidence suggests a prosurvival function for autophagy, but other studies propose a prodeath phenotype. Here, we describe and discuss what we know and what we do not know about various PCD pathways and how the host integrates signals to activate salicylic acid and reactive oxygen pathways that orchestrate cell death. We suggest that it is not cell death as such but rather the processes leading to cell death that contribute to the outcome of a given plant-pathogen interaction.

Programmed cell death in C. elegans, mammals and plants

Programmed cell death (PCD) is the regulated removal of cells within an organism and plays a fundamental role in growth and development in nearly all eukaryotes. In animals, the model organism Caenorhabditis elegans (C. elegans) has aided in elucidating many of the pathways involved in the cell death process. Various analogous PCD processes can also be found within mammalian PCD systems, including vertebrate limb development. Plants and animals also appear to share hallmarks of PCD, both on the cellular and molecular level. Cellular events visualized during plant PCD resemble those seen in animals including: nuclear condensation, DNA fragmentation, cytoplasmic condensation, and plasma membrane shrinkage. Recently the molecular mechanisms involved in plant PCD have begun to be elucidated. Although few regulatory proteins have been identified as conserved across all eukaryotes, molecular features such as the participation of caspase-like proteases, Bcl-2-like family members and mitochondrial proteins appear to be conserved between plant and animal systems. Transgenic expression of mammalian and C. elegans pro- and anti-apoptotic genes in plants has been observed to dramatically influence the regulatory pathways of plant PCD. Although these genes often show little to no sequence similarity they can frequently act as functional substitutes for one another, thus suggesting that action may be more important than sequence resemblance. Here we present a summary of these findings, focusing on the similarities, between mammals, C. elegans, and plants. An emphasis will be placed on the mitochondria and its role in the cell death pathway within each organism. Through the comparison of these systems on both a cellular and molecular level we can begin to better understand PCD in plant systems, and perhaps shed light on the pathways, which are controlling the process. This manuscript adds to the field of PCD in plant systems by profiling apoptotic factors, to scale on a protein level, and also by filling in gaps detailing plant apoptotic factors not yet amalgamated within the literature.

Apoptosis-related genes confer resistance to Fusarium wilt in transgenic 'Lady Finger' bananas

Fusarium wilt, caused by Fusarium oxysporum f. sp. cubense (Foc), is one of the most devastating diseases of banana (Musa spp.). Apart from resistant cultivars, there are no effective control measures for the disease. We investigated whether the transgenic expression of apoptosis-inhibition-related genes in banana could be used to confer disease resistance. Embryogenic cell suspensions of the banana cultivar, 'Lady Finger', were stably transformed with animal genes that negatively regulate apoptosis, namely Bcl-xL, Ced-9 and Bcl-2 3' UTR, and independently transformed plant lines were regenerated for testing. Following a 12-week exposure to Foc race 1 in small-plant glasshouse bioassays, seven transgenic lines (2 × Bcl-xL, 3 × Ced-9 and 2 × Bcl-2 3' UTR) showed significantly less internal and external disease symptoms than the wild-type susceptible 'Lady Finger' banana plants used as positive controls. Of these, one Bcl-2 3' UTR line showed resistance that was equivalent to that of wild-type Cavendish bananas that were included as resistant negative controls. Further, the resistance of this line continued for 23-week postinoculation at which time the experiment was terminated. Using TUNEL assays, Foc race 1 was shown to induce apoptosis-like features in the roots of wild-type 'Lady Finger' plants consistent with a necrotrophic phase in the life cycle of this pathogen. This was further supported by the observed reduction in these effects in the roots of the resistant Bcl-2 3' UTR-transgenic line. This is the first report on the generation of transgenic banana plants with resistance to Fusarium wilt.

Expression of baculovirus anti-apoptotic p35 gene in tobacco enhances tolerance to abiotic stress

Expression of baculovirus anti-apoptotic p35 gene in plants on biotic stress responses has been well studied but its function on abiotic stress has not been documented. In the present study, the p35 gene from Autographa californica multiple nucleopolyhedrovirus (AcMNPV) was expressed in tobacco. A detached leaf assay was used to test tolerance of p35 transgenic plants to various abiotic stress responses. Expression of p35 gene in tobacco gave tolerance to treatment with methanol and H2O2 and also delayed leaf senescence under starvation in the dark. Germination of T(0) seeds on NaCl-containing medium also demonstrated to increase salt tolerance.

Cell death upon H(2)O(2) induction in the unicellular green alga Micrasterias

In the present study, we investigated whether the unicellular green alga Micrasterias denticulata is capable of executing programmed cell death (PCD) upon experimental induction, and which morphological, molecular and physiological hallmarks characterise this. This is particularly interesting as unicellular freshwater green algae growing in shallow bog ponds are exposed to extreme environmental conditions, and the capacity to perform PCD may be an important strategy to guarantee survival of the population. The theoretically 'immortal' alga Micrasterias is an ideal object for such investigations as it has served as a cell biological model system for many years and details on its growth properties, physiology and ultrastructure throughout the cell cycle are well known. Treatments with low concentrations of H(2)O(2) are known to induce PCD in other organisms, resulting in severe ultrastructural changes to organelles, as observed in TEM. These include deformation and part disintegration of mitochondria, abnormal dilatation of cisternal rims of dictyosomes, occurrence of multivesicular bodies, an increase in the number of ER compartments, and slight condensation of chromatin. Additionally, a statistically significant increase in caspase-3-like activity was detected, which was abrogated by a caspase-3 inhibitor. Photosynthetic activity measured by fast chlorophyll fluorescence decreased as a consequence of H(2)O(2) exposure, whereas pigment composition, except for a reduction in carotenoids, was the same as in untreated controls. TUNEL positive staining and ladder-like degradation of DNA, both frequently regarded as a hallmark of PCD in higher plants, could only be detected in dead Micrasterias cells.

Plant programmed cell death: can't live with it; can't live without it

The decision of whether a cell should live or die is fundamental for the wellbeing of all organisms. Despite intense investigation into cell growth and proliferation, only recently has the essential and equally important idea that cells control/programme their own demise for proper maintenance of cellular homeostasis gained recognition. Furthermore, even though research into programmed cell death (PCD) has been an extremely active area of research there are significant gaps in our understanding of the process in plants. In this review, we discuss PCD during plant development and pathogenesis, and compare/contrast this with mammalian apoptosis.

Bcl-xL transformed peanut (Arachis hypogaea L.) exhibits paraquat tolerance

The human Bcl-xL gene was transformed into peanut cultivar Georgia Green via microprojectile bombardment. Following selection on hygromycin-containing medium and regeneration, eighty hygromycin-resistant callus clusters were recovered. Southern blot analysis of ten fertile lines revealed multiple insertions of the Bcl-xL transgene in most lines. Western blot analysis of primary plants and T1 progenies demonstrated detectable levels of Bcl-xL expression in four transgenic lines. We could not detect Bcl-xL protein in other tested lines even though transcripts were identified by RT-PCR and northern blot. Three of the western-positive transgenic lines either were sterile or the progenies lost the expressive copy of Bcl-xL. Only T1 progenies from line BX25-4-2a-19 continued to express an intermediate level of Bcl-xL. This line demonstrated paraquat tolerance at the 5 microM level. Tolerance to salt of T1 and T2 seeds from seven other transgenic lines also was tested, but no tolerance was found in these lines. A high level of Bcl-xL transgene expression may be deleterious to plant growth and development even though the gene may confer tolerance to other abiotic and biotic stresses such as drought and pathogens.

Expression of animal CED-9 anti-apoptotic gene in tobacco modifies plasma membrane ion fluxes in response to salinity and oxidative stress

Apoptosis, one form of programmed cell death (PCD), plays an important role in mediating plant adaptive responses to the environment. Recent studies suggest that expression of animal anti-apoptotic genes in transgenic plants may significantly improve a plant's ability to tolerate a variety of biotic and abiotic stresses. The underlying cellular mechanisms of this process remain unexplored. In this study, we investigated specific ion flux "signatures" in Nicotiana benthamiana plants transiently expressing CED-9 anti-apoptotic gene and undergoing salt- and oxidative stresses. Using a range of electrophysiological techniques, we show that expression of CED-9 increased plant salt and oxidative stress tolerance by altering K(+) and H(+) flux patterns across the plasma membrane. Our data shows that PVX/CED-9 plants are capable of preventing stress-induced K(+) efflux from mesophyll cells, so maintaining intracellular K(+) homeostasis. We attribute these effects to the ability of CED-9 to control at least two types of K(+)-permeable channels; outward-rectifying depolarization-activating K(+) channels (KOR) and non-selective cation channels (NSCC). A possible scenario linking CED-9 expression and ionic relations in plant cell is suggested. To the best of our knowledge, this study is the first to link "ion flux signatures" and mechanisms involved in regulation of PCD in plants.

Bcl-2 proteins link programmed cell death with growth and morphogenetic adaptations in the fungal plant pathogen Colletotrichum gloeosporioides

Proteins belonging to the Bcl-2 family regulate apoptosis in mammals by controlling mitochondria efflux of cytochrome c and other apoptosis-related proteins. Homologues of human Bcl-2 proteins are found in different metazoan organisms where they play a similar role, while they seem to be absent in plants and fungi. Nonetheless, Bcl-2 protein members can induce or prevent yeast cell death, suggesting that enough functional conservation exists between apoptotic machineries of mammals and fungi. Here we show that induction or prevention of apoptosis by Bcl-2 proteins in the fungal plant pathogen Colletotrichum gloeosporioides is tightly linked with growth and morphogenetic adaptation that occur throughout the entire fungal life cycle. Isolates expressing the pro-apoptotic Bax protein underwent cell death with apoptotic characteristics, and showed alterations in conidial germination that are associated with pathogenic and non-pathogenic life styles. Isolates expressing the anti-apoptotic Bcl-2 protein had prolonged longevity, were protected from Bax-induced cell death, and exhibited enhanced stress resistance. These isolates also had enhanced mycelium and conidia production, and were hyper virulent to host plants. Our findings show that apoptotic-associated machinery regulates morphogenetic switches, which are critical for proper responses and adaptation fungi to different environments.

Introduction of the anti-apoptotic baculovirus p35 gene in passion fruit induces herbicide tolerance, reduced bacterial lesions, but does not inhibits passion fruit woodiness disease progress induced by cowpea aphid-borne mosaic virus (CABMV)

The introduction of anti-apoptotic genes into plants leads to resistance to environmental stress and broad-spectrum disease resistance. The anti-apoptotic gene (p35) from a baculovirus was introduced into the genome of passion fruit plants by biobalistics. Eleven regenerated plants showed the presence of the p35 gene by PCR and/or dot blot hybridization. Transcriptional analysis of regenerated plants showed the presence of specific p35 transcripts in 9 of them. Regenerated plants containing the p35 gene were inoculated with the cowpea aphid-borne mosaic virus (CABMV), the bacterium Xanthomonas axonopodis pv passiflorae, and the herbicide, glufosinate, (Syngenta). None of the plants showed resistance to CABMV. Regenerated plants (p35+) showed less than half of local lesions showed by non-transgenic plants when inoculated with X. axonopodis and some p35+ plants showed increased tolerance to the glufosinate herbicide when compared to non-transgenic plants.

Expression of the Arabidopsis high-affinity hexose transporter STP13 correlates with programmed cell death

We report the biochemical characterization in Xenopus oocytes of the Arabidopsis thaliana membrane protein, STP13, as a high affinity, hexose-specific H(+)-symporter. Studies with kinase activators suggest that it is negatively regulated by phosphorylation. STP13 promoter GFP reporter lines show GFP expression only in the vascular tissue in emerging petals under non-stressed conditions. Quantitative PCR and the pSTP13-GFP plants show induction of STP13 in programmed cell death (PCD) obtained by treatments with the fungal toxin fumonisin B1 and the pathogen Pseudomonas syringae. A role for STP13 in PCD is supported by microarray data from e.g. plants undergoing senescence and a strong correlation between STP13 transcripts and the PCD phenotype in different accelerated cell death (acd11) mutants.