Plant-parasitic-nematodes represent a major threat to the agricultural production of different crops worldwide. Due to the high toxicity of chemical nematicides, it is necessary to develop new control strategies against nematodes. In this respect, filamentous fungi can be an interesting biocontrol alternative. The genus Trichoderma, mycorrhizal and endophytic fungi are the main groups of filamentous fungi studied and used as biological control agents (BCAs) against nematodes as resistance inducers. They are able to reduce the damage caused by plant-parasitic nematodes directly by parasitism, antibiosis, paralysis and by the production of lytic enzymes. But they also minimize harm by space and resource-competition, by providing higher nutrient and water uptake to the plant, or by modifying the root morphology, and/or rhizosphere interactions, that constitutes an advantage for the plant-growth. Besides, filamentous fungi are able to induce resistance against nematodes by activating hormone-mediated (salicylic and jasmonic acid, strigolactones among others) plant-defense mechanisms. Additionally, the alteration of the transport of chemical defense components through the plant or the synthesis of plant secondary metabolites and different enzymes can also contribute to enhancing plant defenses. Therefore, the use of filamentous fungi of the mentioned groups as BCAs is a promising durable biocontrol strategy in agriculture against plant-parasitic nematodes.

Exposure of Arabidopsis plants that were maintained under low light (200 mumol of photons m-2 sec-1) to excess light (2000 mumol of photons m-2 sec-1) for 1 hr caused reversible photoinhibition of photosynthesis. Measurements of photosynthetic parameters and the use of electron transport inhibitors indicated that a novel signal transduction pathway was initiated at plastoquinone and regulated, at least in part, by the redox status of the plastoquinone pool. This signal, which preceded the photooxidative burst of hydrogen peroxide (H2O2) associated with photoinhibition of photosynthesis, resulted in a rapid increase (within 15 min) in mRNA levels of two cytosolic ascorbate peroxidase genes (APX1 and APX2). Treatment of leaves with exogenous reduced glutathione abolished this signal, suggesting that glutathione or the redox status of the glutathione pool has a regulatory impact on this signaling pathway. During recovery from photooxidative stress, transcripts for cytosolic glutathione reductase (GOR2) increased, emphasizing the role of glutathione in this stress.

The accumulation of toxic metals and metalloids, such as cadmium (Cd), mercury (Hg), or arsenic (As), as a consequence of various anthropogenic activities, poses a serious threat to the environment and human health. The ability of plants to take up mineral nutrients from the soil can be exploited to develop phytoremediation technologies able to alleviate the negative impact of toxic elements in terrestrial ecosystems. However, we must select plant species or populations capable of tolerating exposure to hazardous elements. The tolerance of plant cells to toxic elements is highly dependent on glutathione (GSH) metabolism. GSH is a biothiol tripeptide that plays a fundamental dual role: first, as an antioxidant to mitigate the redox imbalance caused by toxic metal(loid) accumulation, and second as a precursor of phytochelatins (PCs), ligand peptides that limit the free ion cellular concentration of those pollutants. The sulphur assimilation pathway, synthesis of GSH, and production of PCs are tightly regulated in order to alleviate the phytotoxicity of different hazardous elements, which might induce specific stress signatures. This review provides an update on mechanisms of tolerance that depend on biothiols in plant cells exposed to toxic elements, with a particular emphasis on the Hg-triggered responses, and considering the contribution of hormones to their regulation.

Root-knot nematodes differentiate highly specialized feeding cells in roots (giant cells, GCs), through poorly characterized mechanisms that include extensive transcriptional changes. While global transcriptome analyses have used galls, which are complex root structures that include GCs and surrounding tissues, no global gene expression changes specific to GCs have been described. We report on the differential transcriptome of GCs versus root vascular cells, induced in Arabidopsis by Meloidogyne javanica at a very early stage of their development, 3 days after infection (d.p.i.). Laser microdissection was used to capture GCs and root vascular cells for microarray analysis, which was validated through qPCR and by a promoter-GUS fusion study. Results show that by 3 d.p.i., GCs exhibit major gene repression. Although some genes showed similar regulation in both galls and GCs, the majority had different expression patterns, confirming the molecular distinctiveness of the GCs within the gall. Most of the differentially regulated genes in GCs have no previously assigned function. Comparisons with other transcriptome analyses revealed similarities between GCs and cell suspensions differentiating into xylem cells. This suggests a molecular link between GCs and developing vascular cells, which represent putative GC stem cells. Gene expression in GCs at 3 d.p.i. was also found to be similar to crown galls induced by Agrobacterium tumefaciens, a specialized root biotroph.

Plant-parasitic nematodes (PPNs) interact with plants in different ways, for example, through subtle feeding behavior, migrating destructively through infected tissues, or acting as virus-vectors for nepoviruses. They are all obligate biotrophic parasites as they derive their nutrients from living cells which they modify using pharyngeal gland secretions prior to food ingestion. Some of them can also shield themselves against plant defenses to sustain a relatively long lasting interaction while feeding. This paper is centered on cell types or organs that are newly induced in plants during PPN parasitism, including recent approaches to their study based on molecular biology combined with cell biology-histopathology. This issue has already been reviewed extensively for major PPNs (i.e., root-knot or cyst nematodes), but not for other genera (viz. Nacobbus aberrans, Rotylenchulus spp.). PPNs have evolved with plants and this co-evolution process has allowed the induction of new types of plant cells necessary for their parasitism. There are four basic types of feeding cells: (i) non-hypertrophied nurse cells; (ii) single giant cells; (iii) syncytia; and (iv) coenocytes. Variations in the structure of these cells within each group are also present between some genera depending on the nematode species viz. Meloidogyne or Rotylenchulus. This variability of feeding sites may be related in some way to PPN life style (migratory ectoparasites, sedentary ectoparasites, migratory ecto-endoparasites, migratory endoparasites, or sedentary endoparasites). Apart from their co-evolution with plants, the response of plant cells and roots are closely related to feeding behavior, the anatomy of the nematode (mainly stylet size, which could reach different types of cells in the plant), and the secretory fluids produced in the pharyngeal glands. These secretory fluids are injected through the stylet into perforated cells where they modify plant cytoplasm prior to food removal. Some species do not produce specialized feeding sites (viz. Ditylenchus, Subanguina), but may develop a specialized modification of the root system (e.g., unspecialized root galls or a profusion of roots). This review introduces new data on cell types and plant organs stimulated by PPNs using sources varying from traditional histopathology to new holistic methodologies.

When low–light–grown Arabidopsis rosettes are partially exposed to excess light (EL), the unexposed leaves become acclimated to excess excitation energy (EEE) and consequent photo–oxidative stress. This phenomenon, termed systemic acquired acclimation (SAA), is associated with redox changes in the proximity of photosystem II, changes in foliar H ₂ O ₂ content and induction of antioxidant defences. The induction of extra–plastidial antioxidant systems is important in the protection of the chloroplast under EL conditions. A larger range of transcripts encoding different antioxidant defence enzymes may be induced in the systemically acclimated leaves and these include those encoded by the glutathione peroxidase ( GPX2 ) and glutathione–S–transferase ( GST ) genes, which are also highly induced in the hypersensitive response and associated systemic acquired resistance (SAR) in incompatible plantpathogen interactions. Furthermore, the expression of the SAR–inducible pathogenesis–related protein gene, PR2 , is enhanced in SAA leaves. Wounded leaf tissue also shows enhanced systemic induction of a cytosolic ascorbate peroxidase gene ( APX2 ) under EL conditions. These and other considerations, suggest H ₂ O ₂ and other reactive oxygen species (ROS) could be the common factor in signalling pathways for diverse environmental stresses. These effects may be mediated by changes in the level and redox state of the cellular glutathione pool. Mutants with constitutive expression of a normally EL–inducible APX2 gene have much reduced levels of foliar glutathione. The expression of APX1 and APX3 , encoding cytosolic and peroxisome–associated isoforms, respectively, are also under phytochrome–A–mediated control. The expression of these genes is tightly linked to the greening of plastids in etiolated seedlings. These data suggest that part of the developmental processes that bring about the acclimation of leaves to high light includes the configuration of antioxidant defences. Therefore, the linkage between immediate responses of leaves to EL, acclimation of chloroplasts to EEE and the subsequent changes to leaf form and function in high light could be mediated by the activity of foliar antioxidant defences and changes in the concentration of ROS.