PP2A Phosphatase as a Regulator of ROS Signaling in Plants

TRX h2-PP2AC2 module serves as a convergence node for aluminum stress and leaf senescence signals, regulating cell death via ABA-mediated ROS pathway

ROS/redox signaling plays an important role in the regulation of signal transduction and acclimation pathways activated by multiple abiotic stresses and leaf senescence. However, the regulatory events that produce ROS under different stimuli are far from clear. Here, we report the elucidation of the molecular mechanism of an h type thioredoxin, AhTRX h2, positively regulates Al sensitivity and leaf senescence by promoting ROS. AhTRX h2 transcript levels increased greatly during both natural senescence and Al stress condition in peanut. Ectopic expression of AhTRX h2 in Arabidopsis conferred Al sensitivity as well as premature leaf senescence, manifested by multiple indices, including inhibiting root elongation, severe cell death, and accelerated expression of MC1 and CEX17. AhTRX h2 exhibited similar functions to AtTRX h2, as AhTRX h2 was able to restore the phenotypes of the AtTRX h2 defective mutant (trxh2-4) which showed Al tolerant and late senescence phenotypes. The knock down of AhTRX h2 markedly suppressed Al- and senescence-induced cell death in peanut. AhTRX h2 could recruit catalytic subunit of protein phosphatase 2A (PP2AC2) to form a stable complex. The interaction between AhTRX h2 and AtPP2AC2, as well as AhPP2AC2 and AtTRX h2 was also proved. Overexpression of AhPP2AC2 significantly enhanced Al sensitivity and leaf senescence in Arabidopsis. Protein stability assay revealed that AhTRX h2 was more stable during aging or aluminum stress. Moreover, PP2AC2 could greatly enhance the stability of AhTRX h2 in vivo. Consistent with these observations, overexpression of AhPP2AC2 effectively enhanced AhTRX h2-induced Al sensitivity and precocious leaf senescence. AhTRX h2 and AhPP2AC2 required ABA and ROS in response to cell death under Al stress and senescence, and it was evidence to suggest that ABA acted upstream of ROS in this process. Together, AhTRX h2 and AhPP2AC2 constitute a stable complex that promotes the accumulation of ABA and ROS, effectively regulate cell death. These findings suggest that TRX h2-PP2AC2-mediated pathway may be a widespread mechanism in regulating Al stress and leaf senescence.

The conserved AvrE family of bacterial effectors: functions and targets during pathogenesis

The AvrE family of type III secreted effectors are highly conserved among many agriculturally important phytopathogenic bacteria. Despite their critical roles in the pathogenesis of phytopathogenic bacteria, the molecular functions and virulence mechanisms of these effectors have been largely unknown. However, recent studies have identified host-interacting proteins and demonstrated that AvrE family effectors can form water-permeable channels in the plant plasma membrane (PM) to create a hydrated and nutrient-rich extracellular space (apoplast) required for disease establishment. Here, we summarize these recent discoveries and highlight open questions related to AvrE-targeted host proteins.

Phosphatases: Decoding the Role of Mycorrhizal Fungi in Plant Disease Resistance

Mycorrhizal fungi, a category of fungi that form symbiotic relationships with plant roots, can participate in the induction of plant disease resistance by secreting phosphatase enzymes. While extensive research exists on the mechanisms by which mycorrhizal fungi induce resistance, the specific contributions of phosphatases to these processes require further elucidation. This article reviews the spectrum of mycorrhizal fungi-induced resistance mechanisms and synthesizes a current understanding of how phosphatases mediate these effects, such as the induction of defense structures in plants, the negative regulation of plant immune responses, and the limitation of pathogen invasion and spread. It explores the role of phosphatases in the resistance induced by mycorrhizal fungi and provides prospective future research directions in this field.

Walnut phosphatase 2A proteins interact with basic leucine zipper protein JrVIP1 to regulate osmotic stress response via calcium signaling

Walnut is an important economic tree species that is susceptible to osmotic stress. Scientific cultivation management is an important way to improve the yield and quality of walnuts, which requires understanding the regulatory mechanisms in response to osmotic stress. Therefore, in this study, 15 protein phosphatase 2A (PP2A) genes were identified from the walnut transcriptome (named JrPP2A01~15) and their potential function responses to osmotic stress were elucidated. The open reading frame (ORF) of JrPP2A01~15 ranges from 651 to 1,764 bp in length, the molecular weight of the encoded proteins are 24.15-65.61 kDa, and the theoretical isoelectric points are 4.80-8.37. These JrPP2As were unevenly distributed on 10 chromosomes and divided into five groups based on the composition of conserved domains, motifs, and exon/intron organizations. The five groups are JrPP2AAs, JrPP2AB's, JrPP2AB''s, JrPP2AB55s, and JrPP2ACs, including 1, 5, 2, 3, and 4 members, accordingly. The cis-elements in JrPP2As' promoters were involved in responses to hormone and abiotic stress. Most JrPP2A genes, excluding JrPP2A01, JrPP2A02, JrPP2A05, JrPP2A06, and JrPP2A13, could be induced significantly by PEG6000, NaCl, CaCl2 and ABA. JrPP2A02, JrPP2A05, JrPP2A07, JrPP2A09, and JrPP2A14, could independently interact with a bZIP transcription factor JrVIP1. Moreover, overexpression of JrPP2A07, JrPP2A09, and JrPP2A14 could significantly decrease ROS accumulation while increasing calcium (Ca) uptake exposed to PEG6000 and NaCl stresses, which was mediated by exogenous CaCl2 and ABA. These results suggested that JrPP2A genes play potential key roles in walnut response to drought and salt-inducing osmotic stress involving Ca- and ABA-dependent signaling pathways.

Combined physiological responses and differential expression of drought-responsive genes preliminarily explain the drought resistance mechanism of Lotus corniculatus

Lotus corniculatus L. is a perennial high-quality legume forage species but is vulnerable to drought, and water deficit reduces productivity. To understand the drought response mechanism of L. corniculatus , we investigated physiological responses under drought stress and constructed suppression subtractive hybridisation (SSH) cDNA libraries to isolate drought-inducible genes and quantitatively study the expression levels of candidate drought- responsive genes. Genes encoding calmodulin-like protein, mitogen-activated protein kinase, indole-3-acetic acid-induced protein, ser/thr-protein phosphatase homolog-related proteins, and β -galactosidase-related protein with hydrolysis activity were isolated and considered the main factors that explained the resistance of L. corniculatus to drought. Approximately 632 expressed sequence tags (ESTs) were identified and confirmed in the constructed SSH library. The Gene Ontology (GO) analysis revealed that these genes were involved mainly in transcription processes, protein synthesis, material metabolism, catalytic reactions, sugar metabolism, and photosynthesis. The interaction between the functions of these drought-related genes and the physiological responses preliminarily explains the drought resistance mechanisms of L. corniculatus .

Adaptation of protein phosphatases in Oryza sativa and Cucumis sativus to microcystins

Microcystins (MCs) in irrigation water could inhibit crop growth and yield. Protein phosphatases (PPs) play an important role in regulating physiological mechanisms in plants to adapt abiotic stresses. To clarify the adaptation mechanism in plants to MCs stress, we compared PPs in rice and cucumber leaves by analyzing PPs total activity, protein phosphatase-2A (PP2A) activity and expression, as well as related growth and gas exchange parameters. After 7-day exposure of MCs (5 ~ 100 µg/L) and 7-day recovery without MCs, rice showed higher tolerance to MCs by analyzing dry weight and gas exchange parameters. Both crops may regulate PPs activity to adapt MCs stress by increasing the expression of genes encoding PPs. Among them, PP2A activity in two crops showed more sensitivity to MCs than total PPs activity. In addition, the higher expressions of PP2A catalytic and regulatory subunits and lower decrease PP2A activity were observed in rice leaves compared to cucumber. All results suggest that the expression levels of PP2A subunits could play a role in maintaining the activity of PP2A to regulating plant tolerance to MCs stress.

A genome-wide association study identifies novel players in Na and Fe homeostasis in Arabidopsis thaliana under alkaline-salinity stress

In nature, multiple stress factors occur simultaneously. The screening of natural diversity panels and subsequent Genome-Wide Association Studies (GWAS) is a powerful approach to identify genetic components of various stress responses. Here, the nutritional status variation of a set of 270 natural accessions of Arabidopsis thaliana grown on a natural saline-carbonated soil is evaluated. We report significant natural variation on leaf Na (LNa) and Fe (LFe) concentrations in the studied accessions. Allelic variation in the NINJA and YUC8 genes is associated with LNa diversity, and variation in the ALA3 is associated with LFe diversity. The allelic variation detected in these three genes leads to changes in their mRNA expression and correlates with plant differential growth performance when plants are exposed to alkaline salinity treatment under hydroponic conditions. We propose that YUC8 and NINJA expression patters regulate auxin and jasmonic signaling pathways affecting plant tolerance to alkaline salinity. Finally, we describe an impairment in growth and leaf Fe acquisition associated with differences in root expression of ALA3, encoding a phospholipid translocase active in plasma membrane and the trans Golgi network which directly interacts with proteins essential for the trafficking of PIN auxin transporters, reinforcing the role of phytohormonal processes in regulating ion homeostasis under alkaline salinity.

Genome-Wide Identification and Expression Analysis of the Thioredoxin (Trx) Gene Family Reveals Its Role in Leaf Rust Resistance in Wheat (Triticum aestivum L.)

Bread wheat (Triticum aestivum L.; Ta) is the staple cereal crop for the majority of the world’s population. Leaf rust disease caused by the obligate fungal pathogen, Puccinia triticina L., is a biotrophic pathogen causing significant economic yield damage. The alteration in the redox homeostasis of the cell caused by various kinds of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in response to pathogenic infections is controlled by redox regulators. Thioredoxin (Trx) is one of the redox regulators with low molecular weight and is thermostable. Through a genome-wide approach, forty-two (42) wheat Trx genes (TaTrx) were identified across the wheat chromosome groups A, B, and D genomes containing 12, 16, and 14 Trx genes, respectively. Based on in silico expression analysis, 15 TaTrx genes were selected and utilized for further experimentation. These 15 genes were clustered into six groups by phylogenetic analysis. MicroRNA (miRNA) target analysis revealed eight different miRNA-targeted TaTrx genes. Protein–protein interaction (PPI) analysis showed TaTrx proteins interact with thioredoxin reductase, peroxiredoxin, and uncharacterized proteins. Expression profiles resulting from quantitative real-time PCR (qRT-PCR) revealed four TaTrx genes (TaTrx11-5A, TaTrx13-5B, TaTrx14-5D, and TaTrx15-3B) were significantly induced in response to leaf rust infection. Localization of ROS and its content estimation and an assay of antioxidant enzymes and expression analysis suggested that Trx have been involved in ROS homeostasis at span 24HAI-72HAI during the leaf rust resistance.

Protein Phosphatase 2A Catalytic Subunit PP2A-1 Enhances Rice Resistance to Sheath Blight Disease

Rice (Oryza sativa) production is damaged to a great extent by sheath blight disease (ShB). However, the defense mechanism in rice against this disease is largely unknown. Previous transcriptome analysis identified a significantly induced eukaryotic protein phosphatase 2A catalytic subunit 1 (PP2A-1) after the inoculation of Rhizoctonia solani. Five genes encoding PP2A exist in rice genome, and these five genes are ubiquitously expressed in different tissues and stages. Inoculation of R. solani showed that the genome edited pp2a-1 mutants using the CRISPR/Cas9 were more susceptible to ShB than the wild-type control, but other PP2A gene mutants exhibited similar response to ShB compared to wild-type plants. In parallel, PP2A-1 expression level was higher in the activation tagging line, and PP2A-1 overexpression inhibited plant height and promoted the resistance to ShB. PP2A-1-GFP was localized in the cytoplasm and nucleus. In addition, R. solani-dependent induction kinetics of pathogen-related genes PBZ1 and PR1b was lower in pp2a-1 mutants but higher in PP2A-1 activation line compared to those in the wild-type. In conclusion, our analysis shows that PP2A-1 is a member of protein phosphatase, which regulates rice resistance to ShB. This result broadens the understanding of the defense mechanism against ShB and provides a potential target for rice breeding for disease resistance.

Subcellular Alterations Induced by Cyanotoxins in Vascular Plants-A Review

Phytotoxicity of cyanobacterial toxins has been confirmed at the subcellular level with consequences on whole plant physiological parameters and thus growth and productivity. Most of the data are available for two groups of these toxins: microcystins (MCs) and cylindrospermopsins (CYNs). Thus, in this review we present a timely survey of subcellular cyanotoxin effects with the main focus on these two cyanotoxins. We provide comparative insights into how peculiar plant cellular structures are affected. We review structural changes and their physiological consequences induced in the plastid system, peculiar plant cytoskeletal organization and chromatin structure, the plant cell wall, the vacuolar system, and in general, endomembrane structures. The cyanotoxins have characteristic dose-and plant genotype-dependent effects on all these structures. Alterations in chloroplast structure will influence the efficiency of photosynthesis and thus plant productivity. Changing of cell wall composition, disruption of the vacuolar membrane (tonoplast) and cytoskeleton, and alterations of chromatin structure (including DNA strand breaks) can ultimately lead to cell death. Finally, we present an integrated view of subcellular alterations. Knowledge on these changes will certainly contribute to a better understanding of cyanotoxin–plant interactions.

Identification and Functional Analysis of Two Purple Acid Phosphatases AtPAP17 and AtPAP26 Involved in Salt Tolerance in Arabidopsis thaliana Plant

Tolerance to salinity is a complex genetic trait including numerous physiological processes, such as metabolic pathways and gene networks; thereby, identification of genes indirectly affecting, as well as those directly influencing, is of utmost importance. In this study, we identified and elucidated the functional characterization of AtPAP17 and AtPAP26 genes, as two novel purple acid phosphatases associated with high-salt tolerance in NaCl-stressed conditions. Here, the overexpression of both genes enhanced the expression level of AtSOS1, AtSOS2, AtSOS3, AtHKT1, AtVPV1, and AtNHX1 genes, involving in the K+/Na+ homeostasis pathway. The improved expression of the genes led to facilitating intracellular Na+ homeostasis and decreasing the ion-specific damages occurred in overexpressed genotypes (OEs). An increase in potassium content and K+/Na+ ratio was observed in OE17 and OE26 genotypes as well; however, lower content of sodium accumulated in these plants at 150 mM NaCl. The overexpression of these two genes resulted in the upregulation of the activity of the catalase, guaiacol peroxidase, and ascorbate peroxidase. Consequently, the overexpressed plants showed the lower levels of hydrogen peroxide where the lowest amount of lipid peroxidation occurred in these lines. Besides the oxidation resistance, the boost of the osmotic regulation through the increased proline and glycine-betaine coupled with a higher content of pigments and carbohydrates resulted in significantly enhancing biomass production and yield in the OEs under 150 mM NaCl. High-salt stress was also responsible for a sharp induction on the expression of both PAP17 and PAP26 genes. Our results support the hypothesis that these two phosphatases are involved in plant responses to salt stress by APase activity and/or non-APase activity thereof. The overexpression of PAP17 and PAP26 could result in increasing the intracellular APase activity in both OEs, which exhibited significant increases in the total phosphate and free Pi content compared to the wild-type plants. Opposite results witnessed in mutant genotypes (Mu17, Mu26, and DM), associating with the loss of AtPAP17 and AtPAP26 functions, clearly confirmed the role of these two genes in salt tolerance. Hence, these genes can be used as candidate genes in molecular breeding approaches to improve the salinity tolerance of crop plants.

The Ubiquitin Switch in Plant Stress Response

Ubiquitin is a 76 amino acid polypeptide common to all eukaryotic organisms. It functions as a post-translationally modifying mark covalently linked to a large cohort of yet poorly defined protein substrates. The resulting ubiquitylated proteins can rapidly change their activities, cellular localization, or turnover through the 26S proteasome if they are no longer needed or are abnormal. Such a selective modification is essential to many signal transduction pathways particularly in those related to stress responses by rapidly enhancing or quenching output. Hence, this modification system, the so-called ubiquitin-26S proteasome system (UPS), has caught the attention in the plant research community over the last two decades for its roles in plant abiotic and biotic stress responses. Through direct or indirect mediation of plant hormones, the UPS selectively degrades key components in stress signaling to either negatively or positively regulate plant response to a given stimulus. As a result, a tightly regulated signaling network has become of much interest over the years. The ever-increasing changes of the global climate require both the development of new crops to cope with rapid changing environment and new knowledge to survey the dynamics of ecosystem. This review examines how the ubiquitin can switch and tune plant stress response and poses potential avenues to further explore this system.

Genomic Analysis of Soybean PP2A-B ' ' Family and Its Effects on Drought and Salt Tolerance

Abiotic stresses induce the accumulation of reactive oxygen species (ROS) and significantly affect plant growth. Protein phosphatase 2A (PP2A) plays an important role in controlling intracellular and extracellular ROS signals. However, the interaction between PP2A, ROS, and stress tolerance remains largely unclear. In this study, we found that the B ' ' subunit of PP2A (PP2A-B ' ' ) can be significantly induced and was analyzed using drought- and salt-induced soybean transcriptome data. Eighty-three soybean PP2A-B ' ' genes were identified from the soybean genome via homologous sequence alignment, which was distributed across 20 soybean chromosomes. Among soybean PP2A-B ' ' family genes, 26 GmPP2A-B ' ' members were found to be responsive to drought and salt stresses in soybean transcriptome data. Quantitative PCR (qPCR) analysis demonstrated that GmPP2A-B ' ' 71 had the highest expression levels under salt and drought stresses. Functional analysis demonstrated that overexpression of GmPP2A-B ' ' 71 in soybeans can improve plant tolerance to drought and salt stresses; however, the interference of GmPP2A-B ' ' 71 in soybean increased the sensibility to drought and salt stresses. Further analysis demonstrated that overexpression of GmPP2A-B ' ' 71 in soybean could enhance the expression levels of stress-responsive genes, particularly genes associated with ROS elimination. These results indicate that PP2A-B ' ' can promote plant stress tolerance by regulating the ROS signaling, which will contribute to improving the drought resistance of crops.

Co-expression network analysis of protein phosphatase 2A (PP2A) genes with stress-responsive genes in Arabidopsis thaliana reveals 13 key regulators

Abiotic and biotic stresses adversely affect plant growth and development and eventually result in less yield and threaten food security worldwide. In plants, several studies have been carried out to understand molecular responses to abiotic and biotic stresses. However, the complete circuitry of stress-responsive genes that plants utilise in response to those environmental stresses are still unknown. The protein phosphatase 2A (PP2A) gene has been known to have a crucial role in abiotic and biotic stresses; but how it regulates the stress response in plants is still not known completely. In this study, we constructed gene co-expression networks of PP2A genes with stress-responsive gene datasets from cold, drought, heat, osmotic, genotoxic, salt, and wounding stresses to unveil their relationships with the PP2A under different conditions of stress. The graph analysis identified 13 hub genes and several influential genes based on closeness centrality score (CCS). Our findings also revealed the count of unique genes present in different settings of stresses and subunits. We also formed clusters of influential genes based on the stress, CCS, and co-expression value. Analysis of cis-regulatory elements (CREs), recurring in promoters of these genes was also performed. Our study has led to the identification of 16 conserved CREs.

Envisioning the immune interactome in Arabidopsis

During plant-pathogen interaction, immune targets were regulated by protein-protein interaction events such as ligand-receptor/co-receptor, kinase-substrate, protein sequestration, activation or repression via post-translational modification and homo/oligo/hetro-dimerisation of proteins. A judicious use of molecular machinery requires coordinated protein interaction among defence components. Immune signalling in Arabidopsis can be broadly represented in successive or simultaneous steps; pathogen recognition at cell surface, Ca2+ and reactive oxygen species signalling, MAPK signalling, post-translational modification, transcriptional regulation and phyto-hormone signalling. Proteome wide interaction studies have shown the existence of interaction hubs associated with physiological function. So far, a number of protein interaction events regulating immune targets have been identified, but their understanding in an interactome view is lacking. We focussed specifically on the integration of protein interaction signalling in context to plant-pathogenesis and identified the key targets. The present review focuses towards a comprehensive view of the plant immune interactome including signal perception, progression, integration and physiological response during plant pathogen interaction.

Chloroplast avoidance movement: a novel paradigm of ROS signalling

The damaging effects of supra-optimal irradiance on plants, often turning to be lethal, may be circumvented by chloroplast avoidance movement which realigns chloroplasts to the anticlinal surfaces of cells (parallel to the incident light), essentially minimizing photon absorption. In angiosperms and many other groups of plants, chloroplast avoidance movement has been identified to be a strong blue light (BL)-dependent process being mediated by actin filaments wherein phototropins are identified as the photoreceptor involved. Studies through the last few decades have identified key molecular mechanisms involving Chloroplast Unusual Positioning 1 (CHUP1) protein and specific chloroplast-actin (cp-actin) filaments. However, the signal transduction pathway from strong BL absorption down to directional re-localization of chloroplasts by actin filaments is complex and ambiguous. Being the immediate cellular products of high irradiance absorption and having properties of remodelling actin as well as phototropin, reactive oxygen species (ROS) deemed to be more able and prompt than any other signalling agent in mediating chloroplast avoidance movement. Although ROS are presently being identified as fundamental component for regulating different plant processes ranging from growth, development and immunity, its role in avoidance movement have hardly been explored in depth. However, few recent reports have demonstrated the direct stimulatory involvement of ROS, especially H₂O₂, in chloroplast avoidance movement with Ca²⁺ playing a pivotal role. With this perspective, the present review discusses the mechanisms of ROS-mediated chloroplast avoidance movement involving ROS-Ca²⁺-actin communication system and NADPH oxidase (NOX)-plasma membrane (PM) H⁺-ATPase positive feed-forward loop. A possible working model is proposed.

PP2A and microtubules function in 5-aminolevulinic acid-mediated H2 O2 signaling in Arabidopsis guard cells

5-aminolevulinic acid (ALA), a plant growth regulator with great application potential in agriculture and horticulture, induces stomatal opening and inhibits stomatal closure by decreasing guard cell H₂ O₂ . However, the mechanisms behind ALA-decreased H₂ O₂ in guard cells are not fully understood. Here, using type 2A protein phosphatase (PP2A) inhibitors, microtubule-stabilizing/disrupting drugs and green fluorescent protein-tagged α-tubulin 6 transgenic Arabidopsis (GFP-TUA6), we find that PP2A and cortical microtubules (MTs) are involved in ALA-regulated stomatal movement. Then, we analyze stomatal responses of Arabidopsis overexpressing C2 catalytic subunit of PP2A (PP2A-C2) and pp2a-c2 mutant to ALA and abscisic acid (ABA) under both light and dark conditions, and show that PP2A-C2 participates in ALA-induced stomatal movement. Furthermore, using pharmacological methods and confocal studies, we reveal that PP2A and MTs function upstream and downstream, respectively, of H₂ O₂ in guard cell signaling. Finally, we demonstrate the role of H₂ O₂ -mediated microtubule arrangement in ALA inhibiting ABA-induced stomatal closure. Our findings indicate that MTs regulated by PP2A-mediated H₂ O₂ decreasing play an important role in ALA guard cell signaling, revealing new insights into stomatal movement regulation.

Comprehensive genomic analysis of the DUF4228 gene family in land plants and expression profiling of ATDUF4228 under abiotic stresses

Background

Domain of unknown function (DUF) proteins represent a number of gene families that encode functionally uncharacterized proteins in eukaryotes. The DUF4228 gene family is one of these families in plants that has not been described previously.

Results

In this study, we performed an extensive comparative analysis of DUF4228 proteins and determined their phylogeny in the plant lineage. A total of 489 high-confidence DUF4228 family members were identified from 14 land plant species, which sub-divided into three distinct phylogenetic groups: group I, group II and group III. A highly conserved DUF4228 domain and motif distribution existed in each group, implying their functional conservation.

To reveal the possible biological functions of these DUF4228 genes, 25 ATDUF4228 sequences from Arabidopsis thaliana were selected for further analysis of characteristics such as their chromosomal position, gene duplications and gene structures. Ka/Ks analysis identified seven segmental duplication events, while no tandemly duplication gene pairs were found in A. thaliana. Some cis-elements responding to abiotic stress and phytohormones were identified in the upstream sequences of the ATDUF4228 genes. Expression profiling of the ATDUF4228 genes under abiotic stresses (mainly osmotic, salt and cold) and protein-protein interaction prediction suggested that some ATDUF4228 genes are may be involved in the pathways of plant resistance to abiotic stresses.

Conclusion

These results expand our knowledge of the evolution of the DUF4228 gene family in plants and will contribute to the elucidation of the biological functions of DUF4228 genes in the future.

The role of reactive oxygen species in the integration of temperature and light signals

The remarkable plasticity of the biochemical machinery in plants allows the integration of a multitude of stimuli, enabling acclimation to a wide range of growth conditions. The integration of information on light and temperature enables plants to sense seasonal changes and adjust growth, defense, and transition to flowering according to the prevailing conditions. By now, the role of reactive oxygen species (ROS) as important signaling molecules has been established. Here, we review recent data on ROS as important components in the integration of light and temperature signaling by crosstalk with the circadian clock and calcium signaling. Furthermore, we highlight that different environmental conditions critically affect the interpretation of stress stimuli, and consequently defense mechanisms and stress outcome. For example, day length plays an important role in whether enhanced ROS production under stress conditions is directed towards activation of redox poising mechanisms or triggering programmed cell death (PCD). Furthermore, a mild increase in temperature can cause down-regulation of immunity and render plants more sensitive to biotrophic pathogens. Taken together, the evidence presented here demonstrates the complexity of signaling pathways and outline the importance of their correct interpretation in context with the given environmental conditions.

Arabidopsis NAP-related proteins (NRPs) contribute to the coordination of plant growth, developmental rate, and age-related pathogen resistance under short days

Plant nucleosome assembly protein-related proteins (NRPs) are histone chaperons involved in nucleosome turnover. Despite this basic cellular function, the Arabidopsis nrp1-1 nrp2-1 knock out mutant has been reported to exhibit only mild seedling root phenotypes and to significantly affect the expression of only few hundred genes Zhu et al. (2006). Here we report that NRP loss-of-function as well as the ectopic overexpression of At NRP1 significantly affected the growth, development, and the pathogen response of Arabidopsis plants under short day conditions. The nrp1-1 nrp2-1 mutant grew faster and flowered weeks earlier than the wild type and the overexpressor. The latter developed slower and flowered at a lower number of leaves than the mutant and the wild type. Moreover, the mutant was more sensitive, the overexpressor was more tolerant to pathogen-induced necrosis correlating with their more adult and juvenile character, respectively. Transcriptomic comparison of mature non-bolting plants agreed with the phenotypes. The presented and other published data indicate that although NRPs might not be absolutely required for normal plant growth and development, their level needs to be controlled to allow the epigenetic coordination of metabolic, growth, defence and developmental processes during the acclimation to unfavourable growth conditions such as short days.

Silencing of the Wheat Protein Phosphatase 2A Catalytic Subunit TaPP2Ac Enhances Host Resistance to the Necrotrophic Pathogen Rhizoctonia cerealis

Eukaryotic type 2A protein phosphatases (protein phosphatase 2A, PP2A) consist of a scaffold subunit A, a regulatory subunit B, and a catalytic subunit C. Little is known about the roles of PP2Ac proteins that are involved in plant responses to necrotrophic fungal pathogens. Sharp eyespot, caused by the necrotrophic fungus Rhizoctonia cerealis, is a destructive disease of wheat (Triticum aestivum), an important staple food crop. Here, we isolated TaPP2Ac-4D from wheat, which encodes a catalytic subunit of the heterotrimeric PP2A, and characterized its properties and role in plant defense response to R. cerealis. Based on the sequence alignment of TaPP2Ac-4D with the draft sequences of wheat chromosomes from the International Wheat Genome Sequencing Consortium (IWGSC), it was found that TaPP2Ac-4D gene is located on the long arm of the wheat chromosome 4D and has two homologs assigned on wheat chromosomes 4A and 4B. Sequence and phylogenetic tree analyses revealed that the TaPP2Ac protein is a typical member of the PP2Ac family and belongs to the subfamily II. TaPP2Ac-4B and TaPP2Ac-4D displayed higher transcriptional levels in the R. cerealis-susceptible wheat cultivar Wenmai 6 than those seen in the resistant wheat line CI12633. The transcriptional levels of TaPP2Ac-4B and TaPP2Ac-4D were significantly elevated in wheat R. cerealis after infection and upon H₂O₂ treatment. Virus-induced gene silencing results revealed that the transcriptional knockdown of TaPP2Ac-4D and TaPP2Ac-4B significantly increased wheat resistance to R. cerealis infection. Meanwhile, the transcriptional levels of certain pathogenesis-related (PR) and reactive oxygen species (ROS)-scavenging enzyme encoding genes were increased in TaPP2Ac-silenced wheat plants. These results suggest that TaPP2Ac-4B and TaPP2Ac-4D negatively regulate defense response to R. cerealis infection possibly through modulation of the expression of certain PR and ROS-scavenging enzyme genes in wheat. This study reveals a novel function of the plant PP2Ac genes in plant immune responses.

Dual TORCs driven and B56 orchestrated signaling network guides eukaryotic cell migration

Different types of eukaryotic cells may adopt seemingly distinct modes of directional cell migration. However, several core aspects are regarded common whether the movement is either ameoboidal or mesenchymal. The region of cells facing the attractive signal is often termed leading edge where lamellipodial structures dominates and the other end of the cell called rear end is often mediating cytoskeletal F-actin contraction involving Myosin-II. Dynamic remodeling of cell-to-matrix adhesion involving integrin is also evident in many types of migrating cells. All these three aspects of cell migration are significantly affected by signaling networks of TorC2, TorC1, and PP2A/B56. Here we review the current views of the mechanistic understanding of these regulatory signaling networks and how these networks affect eukaryotic cell migration.

Protein Phosphatase 2A in the Regulatory Network Underlying Biotic Stress Resistance in Plants

Biotic stress factors pose a major threat to plant health and can significantly deteriorate plant productivity by impairing the physiological functions of the plant. To combat the wide range of pathogens and insect herbivores, plants deploy converging signaling pathways, where counteracting activities of protein kinases and phosphatases form a basic mechanism for determining appropriate defensive measures. Recent studies have identified Protein Phosphatase 2A (PP2A) as a crucial component that controls pathogenesis responses in various plant species. Genetic, proteomic and metabolomic approaches have underscored the versatile nature of PP2A, which contributes to the regulation of receptor signaling, organellar signaling, gene expression, metabolic pathways, and cell death, all of which essentially impact plant immunity. Associated with this, various PP2A subunits mediate post-translational regulation of metabolic enzymes and signaling components. Here we provide an overview of protein kinase/phosphatase functions in plant immunity signaling, and position the multifaceted functions of PP2A in the tightly inter-connected regulatory network that controls the perception, signaling and responding to biotic stress agents in plants.

Protein Phosphatase 2A in the Regulatory Network Underlying Biotic Stress Resistance in Plants

Biotic stress factors pose a major threat to plant health and can significantly deteriorate plant productivity by impairing the physiological functions of the plant. To combat the wide range of pathogens and insect herbivores, plants deploy converging signaling pathways, where counteracting activities of protein kinases and phosphatases form a basic mechanism for determining appropriate defensive measures. Recent studies have identified Protein Phosphatase 2A (PP2A) as a crucial component that controls pathogenesis responses in various plant species. Genetic, proteomic and metabolomic approaches have underscored the versatile nature of PP2A, which contributes to the regulation of receptor signaling, organellar signaling, gene expression, metabolic pathways, and cell death, all of which essentially impact plant immunity. Associated with this, various PP2A subunits mediate post-translational regulation of metabolic enzymes and signaling components. Here we provide an overview of protein kinase/phosphatase functions in plant immunity signaling, and position the multifaceted functions of PP2A in the tightly inter-connected regulatory network that controls the perception, signaling and responding to biotic stress agents in plants.