Protease activity and phytocystatin expression in Arabidopsis thaliana upon Heterodera schachtii infection

Arabidopsis thaliana Phytocystatin 6 Forms Functional Oligomer and Amyloid Fibril States

Cystatins encode a high functional variability not only because of their ability to inhibit different classes of proteases but also because of their propensity to form oligomers and amyloid fibrils. Phytocystatins, essential regulators of protease activity in plants, specifically inhibit papain-like cysteine proteases (PLCPs) and legumains through two distinct cystatin domains. Mammalian cystatins can form amyloid fibrils; however, the potential for amyloid fibril formation of phytocystatins remains unknown. In this study, we demonstrate that Arabidopsis thaliana phytocystatin 6 (AtCYT6) exists as a mixture of monomeric, dimeric, and oligomeric forms in solution. Noncovalent oligomerization was facilitated by the N-terminal cystatin domain, while covalent dimerization occurred through disulfide bond formation in the interdomain linker. The noncovalent dimeric form of AtCYT6 retained activity against its target proteases, papain and legumain, albeit with reduced inhibitory potency. Additionally, we observed the formation of amyloid fibrils by AtCYT6 under acidic pH conditions and upon heating. The amyloidogenic potential could be attributed to the AtCYT6's N-terminal domain (AtCYT6-NTD). Importantly, AtCYT6 amyloid fibrils harbored inhibitory activities against both papain and legumain. These findings shed light on the oligomerization and amyloidogenic behavior of AtCYT6, expanding our understanding of phytocystatin biology and its potential functional implications for plant protease regulation.

Nitric Oxide in Plant Functioning: Metabolism, Signaling, and Responses to Infestation with Ecdysozoa Parasites

Nitric oxide (NO) is an important signaling molecule that is involved in a wide range of physiological processes in plants, including responses to biotic and abiotic stresses. Changes in endogenous NO concentration lead to activation/deactivation of NO signaling and NO-related processes. This paper presents the current state of knowledge on NO biosynthesis and scavenging pathways in plant cells and highlights the role of NO in post-translational modifications of proteins (S-nitrosylation, nitration, and phosphorylation) in plants under optimal and stressful environmental conditions. Particular attention was paid to the interactions of NO with other signaling molecules: reactive oxygen species, abscisic acid, auxins (e.g., indole-3-acetic acid), salicylic acid, and jasmonic acid. In addition, potential common patterns of NO-dependent defense responses against attack and feeding by parasitic and molting Ecdysozoa species such as nematodes, insects, and arachnids were characterized. Our review definitely highlights the need for further research on the involvement of NO in interactions between host plants and Ecdysozoa parasites, especially arachnids.

Proteolytic and Structural Changes in Rye and Triticale Roots under Aluminum Stress

Proteolysis and structural adjustments are significant for defense against heavy metals. The purpose of this study was to evaluate whether the Al³⁺ stress alters protease activity and the anatomy of cereale roots. Azocaseinolytic and gelatinolytic measurements, transcript-level analysis of phytocystatins, and observations under microscopes were performed on the roots of Al³⁺-tolerant rye and tolerant and sensitive triticales exposed to Al³⁺. In rye and triticales, the azocaseinolytic activity was higher in treated roots. The gelatinolytic activity in the roots of rye was enhanced between 12 and 24 h in treated roots, and decreased at 48 h. The gelatinolytic activity in treated roots of tolerant triticale was the highest at 24 h and the lowest at 12 h, whereas in treated roots of sensitive triticale it was lowest at 12 h but was enhanced at 24 and 48 h. These changes were accompanied by increased transcript levels of phytocystatins in rye and triticale-treated roots. Light microscope analysis of rye roots revealed disintegration of rhizodermis in treated roots at 48 h and indicated the involvement of root border cells in rye defense against Al³⁺. The ultrastructural analysis showed vacuoles containing electron-dense precipitates. We postulate that proteolytic-antiproteolytic balance and structural acclimation reinforce the fine-tuning to Al³⁺.

Molecular investigation of proteinase inhibitor (PI) gene in tomato plants induced by Meloidogyne species

Background

The plant parasitic nematode genus Meloidogyne parasitize almost all flowering crops. Plants respond with a variety of morphological and molecular mechanisms to reduce the effects of pathogens. Proteinase inhibitors (PI), a special group of plant proteins which are small proteins, involve in protective role in the plants attacked by microorganisms. Still, the plant response using PI against nematodes has not been well understood. Therefore, this study was aimed to determine the expression of proteinase inhibitor I (PI-I) gene subsequent the infection of M. incognita, M. javanica, and M. chitwoodi in tomato plants post nematode infections. Molecular methods were used to determine the PI gene expressions at different days post nematode infections in host tissues.

Results

Results revealed that the population of M. incognita species reached the highest level of nematode population followed by M. javanica and M. chitwoodi, respectively. All Meloidogyne species induced expression of PI-I gene reached at the utmost level at 3 days post infection (dpi) in host tissues. Relative gene expression level was sharply dropped at 7 dpi, 14 dpi, and 21 dpi in M. incognita induced gene expression in host tissues. Similar results were observed in host tissues after infection of M. javanica and M. chitwoodi.

Conclusions

The commonalities of plant response across a diverse Meloidogyne species interaction and the expression of PI gene may be related to plant defense system. Increased level of PI gene expressions in early infection days in host tissues induced by parasitic nematodes may share resemblances to the mechanisms of resistance on biotrophic interactions.

Reactive oxygen species metabolism and photosynthetic performance in leaves of Hordeum vulgare plants co-infested with Heterodera filipjevi and Aceria tosichella

KEY MESSAGE

Defence responses of cyst nematode and/or wheat curl mite infested barley engage the altered reactive oxygen species production, antioxidant machinery, carbon dioxide assimilation and photosynthesis efficiency. The primary aim of this study was to determine how barley responds to two pests infesting separately or at once; thus barley was inoculated with Heterodera filipjevi (Madzhidov) Stelter (cereal cyst nematode; CCN) and Aceria tosichella Keifer (wheat curl mite; WCM). To verify hypothesis about the involvement of redox metabolism and photosynthesis in barley defence responses, biochemical, photosynthesis efficiency and chlorophyll a fluorescence measurements as well as transmission electron microscopy were implemented. Inoculation with WCM (apart from or with CCN) brought about a significant suppression in the efficiency of electron transport outside photosystem II reaction centres. This limitation was an effect of diminished pool of rapidly reducing plastoquinone and decreased total electron carriers. Infestation with WCM (apart from or with CCN) also significantly restricted the electron transport on the photosystem I acceptor side, therefore produced reactive oxygen species oxidized lipids in cells of WCM and double infested plants and proteins in cells of WCM-infested plants. The level of hydrogen peroxide was significantly decreased in double infested plants because of glutathione-ascorbate cycle involvement. The inhibition of nitrosoglutathione reductase promoted the accumulation of S-nitrosoglutathione increasing antioxidant capacity in cells of double infested plants. Moreover, enhanced arginase activity in WCM-infested plants could stimulate synthesis of polyamines participating in plant antioxidant response. Infestation with WCM (apart from or with CCN) significantly reduced the efficiency of carbon dioxide assimilation by barley leaves, whereas infection only with CCN expanded photosynthesis efficiency. These were accompanied with the ultrastructural changes in chloroplasts during CCN and WCM infestation.

Effects of lead, cadmium and zinc on protein changes in Silene vulgaris shoots cultured in vitro

In the present research, Silene vulgaris as a representative species growing on both unpolluted and heavy metal (HM) polluted terrains were used to identify ecotype-specific responses to metallic stress. Growth, cell ultrastructure and element accumulations were compared between non-metallicolous (NM), calamine (CAL) and serpentine (SER) specimens untreated with HMs and treated with Pb, Cd and Zn ions under in vitro conditions. Moreover, proteins' modifications related to their level, carbonylation and degradations via vacuolar proteases were verified and linked with potential mechanisms to cope with ions toxicity. Our experiment revealed diversified strategy of HM uptake in NM and both metallicolous ecotypes, in which antagonistic relationship of Zn and Pb/Cd ions provided survival benefits for the whole organism. Despite this similarity, growth rate and metabolic pathways induced in CAL and SER shoots varied significantly. Exposition to HMs in CAL culture led to drop in protein level by approximately 16% compared to the control. This parameter nearly correlated with the enhanced activity of proteases at pH 5.2 as well as possible glutamate changes to proline and reduced glutathione, resulting in intensified growth and first signs of cell senescence. In turn, SER shoots were characterized by growth retardation (to 53% of the control), although protein level and carbonylation were not modified, while a deeper insight into protein network showed its remodeling towards production of polyamines and 2-oxoglutarate delivered to the Krebs cycle. Contrary, an uncontrolled HM influx in NM shoots contributed to morpho-structural disorders accompanied by an increase activity of proteases involved in the degradation of oxidized proteins, what pointed to metal-induced autophagy. Taken together, S. vulgaris ecotypes respond to stress by triggering various mechanisms engaged their survival and/or death under HM treatment.

Cyst Nematode Infection Elicits Alteration in the Level of Reactive Nitrogen Species, Protein S-Nitrosylation and Nitration, and Nitrosoglutathione Reductase in Arabidopsis thaliana Roots

Reactive nitrogen species (RNS) are redox molecules important for plant defense against pathogens. The aim of the study was to determine whether the infection by the beet cyst nematode Heterodera schachtii disrupts RNS balance in Arabidopsis thaliana roots. For this purpose, measurements of nitric oxide (NO), peroxynitrite (ONOO⁻), protein S-nitrosylation and nitration, and nitrosoglutathione reductase (GSNOR) in A. thaliana roots from 1 day to 15 days post-inoculation (dpi) were performed. The cyst nematode infection caused generation of NO and ONOO⁻ in the infected roots. These changes were accompanied by an expansion of S-nitrosylated and nitrated proteins. The enzyme activity of GSNOR was decreased at 3 and 15 dpi and increased at 7 dpi in infected roots, whereas the GSNOR1 transcript level was enhanced over the entire examination period. The protein content of GSNOR was increased in infected roots at 3 dpi and 7 dpi, but at 15 dpi, did not differ between uninfected and infected roots. The protein of GSNOR was detected in plastids, mitochondria, cytoplasm, as well as endoplasmic reticulum and cytoplasmic membranes. We postulate that RNS metabolism plays an important role in plant defense against the beet cyst nematode and helps the fine-tuning of the infected plants to stress sparked by phytoparasitic nematodes.

Efficient antioxidant defence systems of spring barley in response to stress induced jointly by the cyst nematode parasitism and cadmium exposure

AIMS

This research aimed to establish how Hordeum vulgare responds to abiotic and biotic stress affecting in tandem.

METHODS

Plants were inoculated with Heterodera filipjevi and treated with cadmium (Cd) concentration (5 μM) that can occur in the cultivated soil. To verify the hypothesis about participation of increased antioxidative defence in H. vulgare under stress, biochemical and microscopic methods were implemented.

RESULTS

The amount of superoxide anions and hydrogen peroxide was diminished in plants that were both nematode-inoculated and cadmium-treated. Superoxide anions were rendered harmless by increased activity of superoxide dismutase, and H₂O₂ was scavenged via Foyer-Halliwell-Asada pathway. The unique enhanced antioxidant capacity of double stressed plants was also linked with the accumulation of S-nitrosoglutathione as nitrosoglutathione reductase activity was inhibited. Furthermore, stimulated activity of arginase in these plants could promote polyamine synthesis and indirectly enhance non-enzymatic antioxidant mechanism. Results indicate that different antioxidants operating together significantly restricted oxidation of lipids and proteins, thus the integrity of cell membranes and protein functions were maintained.

CONCLUSIONS

The ROS deactivation machinery in barley leaves showed an unusual response during stress induced by H. filipjevi infection and cadmium treatment. Plants could induce a multi-component model of stress response, to detoxify Cd ions and efficiently repair stress damage.

Activity profiling of barley vacuolar processing enzymes provides new insights into the plant and cyst nematode interaction

Vacuolar processing enzymes (VPEs) play an important role during regular growth and development and defence responses. Despite substantial attempts to understand the molecular basis of plant-cyst nematode interaction, the mechanism of VPEs functioning during this interaction remains unknown. The second-stage Heterodera filipjevi juvenile penetrates host roots and induces the formation of a permanent feeding site called a syncytium. To investigate whether infection with H. filipjevi alters plant host VPEs, the studies were performed in Hordeum vulgare roots and leaves on the day of inoculation and at 7, 14 and 21 days post-inoculation (dpi). Implementing molecular, biochemical and microscopic methods we identified reasons for modulation of barley VPE activity during interaction with H. filipjevi. Heterodera filipjevi parasitism caused a general decrease of VPE activity in infected roots, but live imaging of VPEs showed that their activity is up-regulated in syncytia at 7 and 14 dpi and down-regulated at 21 dpi. These findings were accompanied by tissue-specific VPE gene expression patterns. Expression of the barley cystatin HvCPI-4 gene was stimulated in leaves but diminished in roots upon infestation. External application of cyclotides that can be produced naturally by VPEs elicits in pre-parasitic juveniles vesiculation of their body, enhanced formation of granules, induction of exploratory behaviour (stylet thrusts and head movements), production of reactive oxygen species (ROS) and final death by methuosis. Taken together, down-regulation of VPE activity through nematode effectors promotes the nematode invasion rates and leads to avoidance of the induction of the plant proteolytic response and death of the invading juveniles.

Structural, physiological and genetic diversification of Silene vulgaris ecotypes from heavy metal-contaminated areas and their synchronous in vitro cultivation

Results provide significant comparison of leaf anatomy, pigment content, antioxidant response and phenolic profile between individuals from miscellaneous populations and describe unified cultivation protocols for further research on stress biology. The plant communities growing on heavy metal-polluted areas have attracted considerable attention due to their unique ability to tolerate enormous amounts of toxic ions. Three ecotypes of Silene vulgaris representing calamine (CAL), serpentine (SER) and non-metallicolous (NM) populations were evaluated to reveal specific adaptation traits to harsh environment. CAL leaves presented a distinct anatomical pattern compared to leaves of SER and NM plants, pointing to their xeromorphic adaptation. These differences were accompanied by divergent accumulation and composition of photosynthetic pigments as well as antioxidant enzyme activity. In CAL ecotype, the mechanism of reactive oxygen species scavenging is based on the joint action of superoxide dismutase and catalase, but in SER ecotype on superoxide dismutase and guaiacol-type peroxidase. On the contrary, the concentration of phenylpropanoids and flavonols in the ecotypes was unchanged, implying the existence of similar pathways of their synthesis/degradation functioning in CAL and SER populations. The tested specimens showed genetic variation (atpA/MspI marker). Based on diversification of S. vulgaris populations, we focused on the elaboration of similar in vitro conditions for synchronous cultivation of various ecotypes. The most balanced shoot culture growth was obtained on MS medium containing 0.1 mg l^-1 NAA and 0.25 mg l^-1 BA, while the most abundant callogenesis was observed on MS medium enriched with 0.5 mg l^-1 NAA and 5.0 mg l^-1 BA. For the first time, unified in vitro protocols were described for metallophytes providing the opportunity to conduct basic and applied research on stress biology and tolerance mechanisms under freely controlled conditions.

Plant Cell Wall Proteomics: A Focus on Monocot Species, Brachypodium distachyon, Saccharum spp. and Oryza sativa

Plant cell walls mostly comprise polysaccharides and proteins. The composition of monocots' primary cell walls differs from that of dicots walls with respect to the type of hemicelluloses, the reduction of pectin abundance and the presence of aromatic molecules. Cell wall proteins (CWPs) differ among plant species, and their distribution within functional classes varies according to cell types, organs, developmental stages and/or environmental conditions. In this review, we go deeper into the findings of cell wall proteomics in monocot species and make a comparative analysis of the CWPs identified, considering their predicted functions, the organs analyzed, the plant developmental stage and their possible use as targets for biofuel production. Arabidopsis thaliana CWPs were considered as a reference to allow comparisons among different monocots, i.e., Brachypodium distachyon, Saccharum spp. and Oryza sativa. Altogether, 1159 CWPs have been acknowledged, and specificities and similarities are discussed. In particular, a search for A. thaliana homologs of CWPs identified so far in monocots allows the definition of monocot CWPs characteristics. Finally, the analysis of monocot CWPs appears to be a powerful tool for identifying candidate proteins of interest for tailoring cell walls to increase biomass yield of transformation for second-generation biofuels production.

Changes in proteolytic activity and protein carbonylation in shoots of Alyssum montanum ecotypes under multi-metal stress

The aim of present study was to evaluate the proteolytic response of metallicolous (M) and nonmetallicolous (NM) ecotypes of Alyssum montanum under heavy metals (HMs) stress. Therefore, shoot cultures of tested species grown on medium enriched simultaneously with 0.7 mM ZnSO₄, 3.0 μM Pb(NO₃)₂ and 16.4 μM CdCl₂ and these concentration corresponded to the content of their soluble forms marked in calamine substrate. After 8 weeks of cultivation, the overall protease activity (azocaseinolytic) and determination of the proteolytic (gelatinolytic) enzymes profile were estimated in HMs-treated and untreated specimens. The proteins of NM specimens were more susceptible to proteolysis induced by HMs than proteins of M ones. It was found that applied HMs ions caused an increase of protease activity in HMs-treated shoots of NM ecotype that was accompanied by diminished total soluble proteins content and their higher carbonylation. In contrast, the activities of the neutral proteases and metal-dependent serine proteases decreased in HMs-treated shoots of M ecotype. Our results have revealed significant differences at the protein metabolism level in contrasting A. montanum ecotypes cultured in vitro in the presence of HMs.

Expression of both Arabidopsis γ-tubulin genes is essential for development of a functional syncytium induced by Heterodera schachtii

After initial up-regulation, expression of TUBG1 and TUBG2 is significantly down-regulated in mature syncytia, but lack of expression of either of γ-tubulin genes reduces numbers of nematode infections and developing females. Infective second stage juveniles of sedentary plant parasitic nematode Heterodera schachtii invade the root vascular tissue and induce a feeding site, named syncytium, formed as a result of cell hypertrophy and partial cell wall dissolution leading to a multinucleate state. Syncytium formation and maintenance involves a molecular interplay between the plant host and the developing juveniles leading to rearrangements and fragmentation of the plant cytoskeleton. In this study, we investigated the role of two Arabidopsis γ-tubulin genes (TUBG1 and TUBG2), involved in MTs nucleation during syncytium development. Expression analysis revealed that both γ-tubulin's transcript levels changed during syncytium development and after initial up-regulation (1-3 dpi) they were significantly down-regulated in 7, 10 and 15 dpi syncytia. Moreover, TUBG1 and TUBG2 showed distinct immunolocalization patterns in uninfected roots and syncytia. Although no severe changes in syncytium anatomy and ultrastructure in tubg1-1 and tubg2-1 mutants were observed compared to syncytia induced in wild-type plants, nematode infection assays revealed reduced numbers of infecting juveniles and developed female nematodes in mutant lines. Our results indicate that the expression of both TUBG1 and TUBG2 genes, although generally down-regulated in mature syncytia, is essential for successful root infection, development of functional syncytium and nematode maturation.

Systemic changes in photosynthesis and reactive oxygen species homeostasis in shoots of Arabidopsis thaliana infected with the beet cyst nematode Heterodera schachtii

Photosynthetic efficiency and redox homeostasis are important for plant physiological processes during regular development as well as defence responses. The second-stage juveniles of Heterodera schachtii induce syncytial feeding sites in host roots. To ascertain whether the development of syncytia alters photosynthesis and the metabolism of reactive oxygen species (ROS), chlorophyll a fluorescence measurements and antioxidant responses were studied in Arabidopsis thaliana shoots on the day of inoculation and at 3, 7 and 15 days post-inoculation (dpi). Nematode parasitism caused an accumulation of superoxide and hydrogen peroxide molecules in the shoots of infected plants at 3 dpi, probably as a result of the observed down-regulation of antioxidant enzymes. These changes were accompanied by an increase in RNA and lipid oxidation markers. The activities of antioxidant enzymes were found to be enhanced on infection at 7 and 15 dpi, and the content of anthocyanins was elevated from 3 dpi. The fluorescence parameter R_fd , defining plant vitality and the photosynthetic capacity of leaves, decreased by 11% only at 7 dpi, and non-photochemical quenching (NPQ), indicating the effectiveness of photoprotection mechanisms, was about 16% lower at 3 and 7 dpi. As a result of infection, the ultrastructure of chloroplasts was changed (large starch grains and plastoglobules), and more numerous and larger peroxisomes were observed in the mesophyll cells of leaves. We postulate that the joint action of antioxidant enzymes/molecules and photochemical mechanisms leading to the maintenance of photosynthetic efficiency promotes the fine-tuning of the infected plants to oxidative stress induced by parasitic cyst nematodes.