Comparative phosphoproteome analysis of Magnaporthe oryzae-responsive proteins in susceptible and resistant rice cultivars

Integrative transcriptomic, proteomic, and phosphoproteomic analysis on the defense response to Magnaporthe oryzae reveals different expression patterns at the molecular level of durably resistant rice cultivar Mowanggu

Rice blast, caused by Magnaporthe oryzae is one of the most destructive diseases of rice (Oryza sativa L.) in most rice-cultivated areas worldwide. Mowanggu (MWG) is a traditional landrace rice variety in Yunnan with broad-spectrum and durable blast resistance against rice blast fungus. However, the underlying disease-resistance mechanisms remain unknown. An integrative transcriptomic, proteomic, and phosphoproteomic analysis of MWG was performed after inoculation with M. oryzae in this study. The transcriptomic and proteomic results revealed that MWG was moderately correlated at the transcriptional and protein levels. Differentially expressed genes and proteins were up-regulated and significantly enriched in protein phosphorylation, peroxisome, plant-pathogen interactions, phenylpropanoid metabolism and phenylalanine biosynthesis pathways. The phosphoproteomic profile and phosphorylated-protein-interaction network revealed that the altered phosphoproteins were primarily associated with reactive oxygen species (ROS), glycolysis, MAPK signaling pathways, and amino acid biosynthesis. In addition, a series of physiological and biochemical parameters, including ROS, soluble sugars, soluble protein and callus accumulation and defense-related enzyme activities, were used to validate the possible blast resistance mechanisms of MWG. The integrative transcriptomic, proteomic, and phosphoproteomic analysis revealed the different expression patterns at the molecular level of the durably resistant rice cultivar MWG after inoculation with M. oryzae, which provides insight into the molecular mechanisms of rice blast resistance.

Thermosensitivity of pollen: a molecular perspective

A current trend in climate comprises adverse weather anomalies with more frequent and intense temperature events. Heatwaves are a serious threat to global food security because of the susceptibility of crop plants to high temperatures. Among various developmental stages of plants, even a slight rise in temperature during reproductive development proves detrimental, thus making sexual reproduction heat vulnerable. In this context, male gametophyte or pollen development stages are the most sensitive ones. High-temperature exposure induces pollen abortion, reducing pollen viability and germination rate with a concomitant effect on seed yield. This review summarizes the ultrastructural, morphological, biochemical, and molecular changes underpinning high temperature-induced aberrations in male gametophytes. Specifically, we highlight the temperature sensing cascade operating in pollen, involving reactive oxygen species (ROS), heat shock factors (HSFs), a hormones and transcriptional regulatory network. We also emphasize integrating various omics approaches to decipher the molecular events triggered by heat stress in pollen. The knowledge of genes, proteins, and metabolites conferring thermotolerance in reproductive tissues can be utilized to breed/engineer thermotolerant crops to ensure food security.

A Proteomics Insight into Advancements in the Rice-Microbe Interaction

Rice is one of the most-consumed foods worldwide. However, the productivity and quality of rice grains are severely constrained by pathogenic microbes. Over the last few decades, proteomics tools have been applied to investigate the protein level changes during rice-microbe interactions, leading to the identification of several proteins involved in disease resistance. Plants have developed a multi-layered immune system to suppress the invasion and infection of pathogens. Therefore, targeting the proteins and pathways associated with the host's innate immune response is an efficient strategy for developing stress-resistant crops. In this review, we discuss the progress made thus far with respect to rice-microbe interactions from side views of the proteome. Genetic evidence associated with pathogen-resistance-related proteins is also presented, and challenges and future perspectives are highlighted in order to understand the complexity of rice-microbe interactions and to develop disease-resistant crops in the future.

Screening of Candidate Effectors from Magnaporthe oryzae by In Vitro Secretomic Analysis

Magnaporthe oryzae is the causal agent of rice blast, one of the most serious diseases of rice worldwide. Secreted proteins play essential roles during a M. oryzae-rice interaction. Although much progress has been made in recent decades, it is still necessary to systematically explore M. oryzae-secreted proteins and to analyze their functions. This study employs a shotgun-based proteomic analysis to investigate the in vitro secretome of M. oryzae by spraying fungus conidia onto the PVDF membrane to mimic the early stages of infection, during which 3315 non-redundant secreted proteins were identified. Among these proteins, 9.6% (319) and 24.7% (818) are classified as classically or non-classically secreted proteins, while the remaining 1988 proteins (60.0%) are secreted through currently unknown secretory pathway. Functional characteristics analysis show that 257 (7.8%) and 90 (2.7%) secreted proteins are annotated as CAZymes and candidate effectors, respectively. Eighteen candidate effectors are selected for further experimental validation. All 18 genes encoding candidate effectors are significantly up- or down-regulated during the early infection process. Sixteen of the eighteen candidate effectors cause the suppression of BAX-mediated cell death in Nicotiana benthamiana by using an Agrobacterium-mediated transient expression assay, suggesting their involvement in pathogenicity related to secretion effectors. Our results provide high-quality experimental secretome data of M. oryzae and will expand our knowledge on the molecular mechanisms of M. oryzae pathogenesis.

A novel elicitor MoVcpo is necessary for the virulence of Magnaporthe oryzae and triggers rice defense responses

Rice blast caused by Magnaporthe oryzae is one of the most important diseases of rice. Elicitors secreted by M. oryzae play important roles in the interaction with rice to facilitate fungal infection and disease development. In recent years, several elicitor proteins have been identified in M. oryzae, and their functions and importance are increasingly appreciated. In this study, we purified a novel elicitor-activity protein from M. oryzae, which was further identified as a vanadium chloroperoxidase (MoVcpo) by MAIDL TOF/TOF MS. The purified MoVcpo induced reactive oxygen species (ROS) accumulation in host cells, up-regulated the expression of multiple defense-related genes, thus significantly enhancing rice resistance against M. oryzae. These results suggested that MoVcpo functions as a pathogen-associated molecular pattern (PAMP) to trigger rice immunity. Furthermore, MoVcpo was highly expressed in the early stage of M. oryzae infection. Deletion of MoVcpo affected spore formation, conidia germination, cell wall integrity, and sensitivity to osmotic stress, but not fungal growth. Interestingly, compared with the wild-type, inoculation with MoVcpo deletion mutant on rice led to markedly induced ROS accumulation, increased expression of defense-related genes, but also lower disease severity, suggesting that MoVcpo acts as both an elicitor activating plant immune responses and a virulence factor facilitating fungal infection. These findings reveal a novel role for vanadium chloroperoxidase in fungal pathogenesis and deepen our understanding of M. oryzae-rice interactions.

MoSDT1 triggers defense response through modulating phosphorylated proteins in rice

MoSDT1, a rice blast fungus transcription factor, is as an inducer to activate defense response through mainly mediating phosphorylated proteins in rice. Pathogen effector proteins play a dual role in infecting the host or triggering a defense response. Our previous research found a Magnaporthe oryzae effector, MoSDT1, which could activate the rice defense response when it was overexpressed in rice. However, we still know little about the mechanisms on how MoSDT1 in vivo or in vitro influences the resistance ability of rice. Our results showed that decreased ROS and increased lignin contents appeared along with significant upregulation of defense-related genes, raffinose synthesis gene, and phenylalanine ammonialyase gene. Moreover, we revealed that the contents of lignin were increased, which was in accordance with the upregulation of its precursor phenylalanine gene despite the fact that the glutamate-/thiamine-responsive genes were inhibited in MoSDT1 transgenic rice, and these indicated that MoSDT1 triggered the defense system of rice in vivo. Interestingly, in vitro studies, we further found that MoSDT1 induced the defense system by ROS synthesis, callose deposition, PR gene expression and SA/JA synthesis/signal genes using the purified prokaryotic expression system in rice plants. In addition, this defense response was confirmed to be activated by the zinc finger domain of MoSDT1 via prokaryotic expression of MoSDT1 truncated mutants in rice plants. To elucidate the regulative effects of MoSDT1 on protein phosphorylation in rice, phosphoproteome analysis was performed in both MoSDT1-transgenic and wild type  rice. We found that MoSDT1 specifically up-regulated the expression levels of a few phosphorylated proteins, which were involved in multiple functions, such as biotic/abiotic stress and growth. In addition, the motifs in these specific proteins ranked the top among the top-five conserved motifs in the MoSDT1-transgenic rice. MoSDT1 played a crucial role in enhancing rice resistance by modulating several genes and signaling pathways.

Cloning and functional analysis of the novel rice blast resistance gene Pi65 in japonica rice

Pi65, a leucine-rich repeat receptor-like kinase (LRR-RLK) domain cloned from Oryza sativa japonica, is a novel rice blast disease resistance gene. Rice blast seriously threatens rice production worldwide. Utilizing the rice blast resistance gene to breed rice blast-resistant varieties is one of the best ways to control rice blast disease. Using a map-based cloning strategy, we cloned a novel rice blast resistance gene, Pi65, from the resistant variety GangYu129 (abbreviated GY129, Oryza sativa japonica). Overexpression of Pi65 in the susceptible variety LiaoXing1 (abbreviated LX1, Oryza sativa japonica) enhanced rice blast resistance, while knockout of Pi65 in GY129 resulted in susceptibility to rice blast disease. Pi65 encodes two transmembrane domains, with 15 LRR domains and one serine/threonine protein kinase catalytic domain, conferring resistance to isolates of Magnaporthe oryzae (abbreviated M. oryzae) collected from Northeast China. There were sixteen amino acid differences between the Pi65 resistance and susceptible alleles. Compared with the Pi65-resistant allele, the susceptible allele exhibited one LRR domain deletion. Pi65 was constitutively expressed in whole plants, and it could be induced in the early stage of M. oryzae infection. Transcriptome analysis revealed that numerous genes associated with disease resistance were specifically upregulated in GY129 24 h post inoculation (HPI); in contrast, photosynthesis and carbohydrate metabolism-related genes were particularly downregulated at 24 HPI, demonstrating that disease resistance-associated genes were activated in GY129 (carrying Pi65) after rice blast fungal infection and that cellular basal metabolism and energy metabolism were inhibited simultaneously. Our study provides genetic resources for improving rice blast resistance and enriches the study of rice blast resistance mechanisms.

Toward Integrated Multi-Omics Intervention: Rice Trait Improvement and Stress Management

Rice (Oryza sativa) is an imperative staple crop for nearly half of the world's population. Challenging environmental conditions encompassing abiotic and biotic stresses negatively impact the quality and yield of rice. To assure food supply for the unprecedented ever-growing world population, the improvement of rice as a crop is of utmost importance. In this era, "omics" techniques have been comprehensively utilized to decipher the regulatory mechanisms and cellular intricacies in rice. Advancements in omics technologies have provided a strong platform for the reliable exploration of genetic resources involved in rice trait development. Omics disciplines like genomics, transcriptomics, proteomics, and metabolomics have significantly contributed toward the achievement of desired improvements in rice under optimal and stressful environments. The present review recapitulates the basic and applied multi-omics technologies in providing new orchestration toward the improvement of rice desirable traits. The article also provides a catalog of current scenario of omics applications in comprehending this imperative crop in relation to yield enhancement and various environmental stresses. Further, the appropriate databases in the field of data science to analyze big data, and retrieve relevant information vis-à-vis rice trait improvement and stress management are described.

Proteomics and Metabolomics Studies on the Biotic Stress Responses of Rice: an Update

Biotic stresses represent a serious threat to rice production to meet global food demand and thus pose a major challenge for scientists, who need to understand the intricate defense mechanisms. Proteomics and metabolomics studies have found global changes in proteins and metabolites during defense responses of rice exposed to biotic stressors, and also reported the production of specific secondary metabolites (SMs) in some cultivars that may vary depending on the type of biotic stress and the time at which the stress is imposed. The most common changes were seen in photosynthesis which is modified differently by rice plants to conserve energy, disrupt food supply for biotic stress agent, and initiate defense mechanisms or by biotic stressors to facilitate invasion and acquire nutrients, depending on their feeding style. Studies also provide evidence for the correlation between reactive oxygen species (ROS) and photorespiration and photosynthesis which can broaden our understanding on the balance of ROS production and scavenging in rice-pathogen interaction. Variation in the generation of phytohormones is also a key response exploited by rice and pathogens for their own benefit. Proteomics and metabolomics studies in resistant and susceptible rice cultivars upon pathogen attack have helped to identify the proteins and metabolites related to specific defense mechanisms, where choosing of an appropriate method to identify characterized or novel proteins and metabolites is essential, considering the outcomes of host-pathogen interactions. Despites the limitation in identifying the whole repertoire of responsive metabolites, some studies have shed light on functions of resistant-specific SMs. Lastly, we illustrate the potent metabolites responsible for resistance to different biotic stressors to provide valuable targets for further investigation and application.

Quantitative Proteome and Phosphoproteome Profiling in Magnaporthe oryzae

The quality and consistency in every sample preparation procedure is crucial for any scientific output. Therefore, it is of utmost importance to have easy, economic, and robust sample preparation protocols. Here, we describe a simple and robust bottom-up proteomic sample preparation strategy for identification and label-free quantification (LFQ) of proteins and phosphoproteins. The presented workflow is designed for large-scale application and involves easy scalable and well-known robust sample preparation techniques, such as cell lysis with SDS buffer under heat, protein precipitation using methanol/chloroform, tryptic digest, and commercially available TiO₂ phosphopeptide enrichment kits. Over a sample set of 48 samples of only 200 mg fungal mycelium each, we quantified a median of 2937 proteins after processing in the IsoQuant software. The median peptide count was 10 peptides per protein leading to a median 65% sequence coverage. In addition, we identified a median of 3324 phosphopeptides (corresponding to 998 phosphoproteins) with 4874 phosphosites per sample. Over all samples, we achieved a median phosphopeptide enrichment efficiency of 77%. The distribution of serine/threonine/tyrosine (S/T/Y) phosphosites was 78.1%/21.2%/0.6%.

Comparative phosphoproteomic analysis of blast resistant and susceptible rice cultivars in response to salicylic acid

BACKGROUND

Salicylic acid (SA) is a significant signaling molecule that induces rice resistance against pathogen invasion. Protein phosphorylation carries out an important regulatory function in plant defense responses, while the global phosphoproteome changes in rice response to SA-mediated defense response has not been reported. In this study, a comparative phosphoproteomic profiling was conducted by two-dimensional gel electrophoresis (2-DE) and mass spectrometry (MS) analysis, with two near-isogenic rice cultivars after SA treatment.

RESULTS

Thirty-seven phosphoprotein spots were differentially expressed after SA treatment, twenty-nine of which were identified by MALDI-TOF/TOF MS, belonging to nine functional categories. Phosphoproteins involved in photosynthesis, antioxidative enzymes, molecular chaperones were similarly expressed in the two cultivars, suggesting SA might alleviate decreases in plant photosynthesis, regulate the antioxidant defense activities, thus improving basal resistance response in both cultivars. Meanwhile, phosphoproteins related to defense, carbohydrate metabolism, protein synthesis and degradation were differentially expressed, suggesting phosphorylation regulation mediated by SA may coordinate complex cellular activities in the two cultivars. Furthermore, the phosphorylation sites of four identified phosphoproteins were verified by NanoLC-MS/MS, and phosphorylated regulation of three enzymes (cinnamoyl-CoA reductase, phosphoglycerate mutase and ascorbate peroxidase) was validated by activity determination.

CONCLUSIONS

Our study suggested that phosphorylation regulation mediated by SA may contribute to the different resistance response of the two cultivars. To our knowledge, this is the first report to measure rice phosphoproteomic changes in response to SA, which provides new insights into molecular mechanisms of SA-induced rice defense.

Proteomics of Rice-Magnaporthe oryzae Interaction: What Have We Learned So Far?

Rice blast disease, caused by Magnaporthe oryzae, is one of the major constraints to rice production, which feeds half of the world's population. Proteomic technologies have been used as effective tools in plant-pathogen interactions to study the biological pathways involved in pathogen infection, plant response, and disease progression. Advancements in mass spectrometry (MS) and apoplastic and plasma membrane protein isolation methods facilitated the identification and quantification of subcellular proteomes during plant-pathogen interaction. Proteomic studies conducted during rice-M. oryzae interaction have led to the identification of several proteins eminently involved in pathogen perception, signal transduction, and the adjustment of metabolism to prevent plant disease. Some of these proteins include receptor-like kinases (RLKs), mitogen-activated protein kinases (MAPKs), and proteins related to reactive oxygen species (ROS) signaling and scavenging, hormone signaling, photosynthesis, secondary metabolism, protein degradation, and other defense responses. Moreover, post-translational modifications (PTMs), such as phosphoproteomics and ubiquitin proteomics, during rice-M. oryzae interaction are also summarized in this review. In essence, proteomic studies carried out to date delineated the molecular mechanisms underlying rice-M. oryzae interactions and provided candidate proteins for the breeding of rice blast resistant cultivars.

Peanut Stunt Virus and Its Satellite RNA Trigger Changes in Phosphorylation in N. benthamiana Infected Plants at the Early Stage of the Infection

Signaling in host plants is an integral part of a successful infection by pathogenic RNA viruses. Therefore, identifying early signaling events in host plants that play an important role in establishing the infection process will help our understanding of the disease process. In this context, phosphorylation constitutes one of the most important post-translational protein modifications, regulating many cellular signaling processes. In this study, we aimed to identify the processes affected by infection with Peanut stunt virus (PSV) and its satellite RNA (satRNA) in Nicotiana benthamiana at the early stage of pathogenesis. To achieve this, we performed proteome and phosphoproteome analyses on plants treated with PSV and its satRNA. The analysis of the number of differentially phosphorylated proteins showed strong down-regulation in phosphorylation in virus-treated plants (without satRNA). Moreover, proteome analysis revealed more down-regulated proteins in PSV and satRNA-treated plants, which indicated a complex dependence between proteins and their modifications. Apart from changes in photosynthesis and carbon metabolism, which are usually observed in virus-infected plants, alterations in proteins involved in RNA synthesis, transport, and turnover were observed. As a whole, this is the first community (phospho)proteome resource upon infection of N. benthamiana with a cucumovirus and its satRNA and this resource constitutes a valuable data set for future studies.

Proteomic analysis of the defense response to Magnaporthe oryzae in rice harboring the blast resistance gene Piz-t

BACKGROUND

Rice blast (caused by Magnaporthe oryzae) is one of the most destructive diseases of rice. While many blast resistance (R) genes have been identified and deployed in rice cultivars, little is known about the R gene-mediated defense mechanism. We used a rice transgenic line harboring the resistance gene Piz-t to investigate the R gene-mediated resistance response to infection.

RESULTS

We conducted comparative proteome profiling of the Piz-t transgenic Nipponbare line (NPB-Piz-t) and wild-type Nipponbare (NPB) inoculated with M. oryzae at 24, 48, 72 h post-inoculation (hpi) using isobaric tags for relative and absolute quantification (iTRAQ) analysis. Comparative analysis of the response of NPB-Piz-t to the avirulent isolate KJ201 and the virulent isolate RB22 identified 114 differentially expressed proteins (DEPs) between KJ201-inoculated NPB-Piz-t (KJ201-Piz-t) and mock-treated NPB-Piz-t (Mock-Piz-t), and 118 DEPs between RB22-inoculated NPB-Piz-t (RB22-Piz-t) and Mock-Piz-t. Among the DEPs, 56 occurred commonly in comparisons KJ201-Piz-t/Mock-Piz-t and RB22-Piz-t/Mock-Piz-t. In a comparison of the responses of NPB and NPB-Piz-t to isolate KJ201, 93 DEPs between KJ201-Piz-t and KJ201-NPB were identified. DEPs in comparisons KJ201-Piz-t/Mock-Piz-t, RB22-Piz-t/Mock-Piz-t and KJ201-Piz-t/KJ201-NPB contained a number of proteins that may be involved in rice response to pathogens, including pathogenesis-related (PR) proteins, hormonal regulation-related proteins, defense and stress response-related proteins, receptor-like kinase, and cytochrome P450. Comparative analysis further identified 7 common DEPs between the comparisons KJ201-Piz-t/KJ201-NPB and KJ201-Piz-t/RB22-Piz-t, including alcohol dehydrogenase I, receptor-like protein kinase, endochitinase, similar to rubisco large subunit, NADP-dependent malic enzyme, and two hypothetical proteins.

CONCLUSIONS

Our results provide a valuable resource for discovery of complex protein networks involved in the resistance response of rice to blast fungus.

Global analysis of sumoylation function reveals novel insights into development and appressorium-mediated infection of the rice blast fungus

Protein post-translational modifications play critical roles in cellular processes, development and stress response. The small ubiquitin-like modifier (SUMO) to proteins is one of the essential modifications in eukaryotes, but its function remains largely unknown in plant pathogenic fungi. We present a comprehensive analysis combined with proteomic, molecular and cellular approaches to explore the roles of sumoylation in the model plant fungal pathogen, Magnaporthe oryzae. We found the SUMO pathway plays key roles in colony growth, conidia formation and virulence to the host, as well as cell-cycle-related phenotypes. Sumoylation is also involved in responding to different stresses. Affinity purification identified 940 putative SUMO substrates, many of which were reported to be involved in development, stress response and infection. Interestingly, four septins were also shown to be sumoylated. Mutation of consensus sumoylation sites in each septin all resulted in reduced virulence to the host and dislocation of septins in appressoria. Moreover, sumoylation is also involved in extracellular secretion of different effector proteins. Our study on the functions of sumoylation provides novel insight into development and infection of the rice blast fungus.

Comparative Phospho- and Acetyl Proteomics Analysis of Posttranslational Modifications Regulating Intestine Regeneration in Sea Cucumbers

Sea cucumbers exposed to stressful circumstances eviscerate most internal organs, and then regenerate them rapidly under favorable environments. Reversible protein phosphorylation and acetylation are major modifications regulating protein function. Herein, for the first time, we perform quantitative phospho- and acetyl proteomics analyses of intestine regeneration in a sea cucumber species Apostichopus japonicus. We identified 1,862 phosphorylation sites in 1,169 proteins, and 712 acetylation sites in 470 proteins. Of the 147 and 251 proteins differentially modified by phosphorylation and acetylation, respectively, most were related to cytoskeleton biogenesis, protein synthesis and modification, signal recognition and transduction, energy production and conversion, or substance transport and metabolism. Phosphorylation appears to play a more important role in signal recognition and transduction than acetylation, while acetylation is of greater importance in posttranslational modification, protein turnover, chaperones; energy production and conversion; amino acid and lipid transport and metabolism. These results expanded our understanding of the regulatory mechanisms of posttranslational modifications in intestine regeneration of sea cucumbers after evisceration.

A proteomic insight into the MSP1 and flg22 induced signaling in Oryza sativa leaves

Previously, we reported a novel Magnaporthe oryzae- secreted protein MSP1, which triggers cell death and pathogen-associated molecular pattern (PAMP)-triggered immune (PTI) responses in rice. To investigate the MSP1 induced defense response in rice at the protein level, we employed a label-free quantitative proteomic approach, in parallel with flg22 treatment, which is a well-known elicitor. Exogenous application of MSP1 to rice leaves induced an oxidative burst, MAPK3/6 activation, and activation of pathogenesis-related genes (DUF26, PBZ, and PR-10). MaxQuant based label free proteome analysis led to the identification of 4167 protein groups of which 433 showed significant differences in response to MSP1 and/or flg22 treatment. Functional annotation of the differential proteins showed that majority of the proteins related to primary, secondary, and lipid metabolism were decreased, while proteins associated mainly with the stress response, post-translational modification and signaling were increased in abundance. Moreover, several peroxidases and receptor kinases were induced by both the elicitors, highlighting their involvement in MSP1 and flg22 induced signaling in rice. Taken together, the results reported here contribute to our understanding of MSP1 and flg22 triggered immune responses at the proteome level, thereby increasing our overall understanding of PTI signaling in rice. BIOLOGICAL SIGNIFICANCE: MSP1 is a M. oryzae secreted protein, which triggers defense responses in rice. Previous reports have shown that MSP1 is required for the pathogenicity of rice blast fungus, however, the exact mechanism of its action and its downstream targets in rice are currently unknown. Identification of the downstream targets is required in order to understand the MSP1 induced signaling in rice. Moreover, key proteins identified could also serve as potential candidates for the generation of disease resistance crops by modulating stress signaling pathways. Therefore, here we employed, for the first time, a label-free quantitative proteomic approach to investigate the MSP1 induced signaling in rice together with flg22. Functional annotation of the differential proteins showed that majority of the proteins related to primary, secondary, and lipid metabolism were decreased, while proteins related to the defense response, signaling and ROS detoxification were majorly increased. Thus, as an elicitor, recombinant MSP1 proteins could be utilized to inducing broad pathogen resistance in crops by priming the local immune responses.

C-terminal Ser/Thr residues are vital for the regulatory role of Ste7 in the asexual cycle and virulence of Beauveria bassiana

The mitogen-activated protein kinase (MAPK) kinase Ste7 has a conserved Ser/Thr loop (S/T-X₄₍₆₎-S/T) that can activate the MAPK Fus3 or Kss1 for the regulation of pheromone response and filamentous growth in model yeast. Here, we show that not only the loop but also four C-terminal Ser/Thr residues are essential for Ste7 to function in the Fus3 cascade of Beauveria bassiana, a filamentous fungal insect pathogen. Mutagenesis of either looped S216/T220 or C-terminal S362 resulted in the same severe defects in conidial germination, hyphal growth, aerial conidiation, and submerged blastospore production as the ste7 deletion, followed by a complete loss of virulence and similarly increased cell sensitivities to osmotic salts, oxidants, heat shock and UV-B irradiation. Mutagenesis of three other Ser/Thr residues (S391, S440, and T485) also caused severe defects in most of the mentioned phenotypes. These defects correlated well with dramatically reduced transcript levels of some phenotype-related genes. These genes encode a transcription factor (CreA) essential for carbon/nitrogen assimilation, developmental activators (BrlA, AbaA, and WetA) and upstream transcription factor (FluG) required for conidiation, P-type N⁺/K⁺ ATPases (Ena1-5) required for intracellular N⁺/K⁺ homeostasis, and antioxidant enzymes involved in multiple stress responses. Our study unveils that the loop and four C-terminal Ser/Thr residues are all vital for the regulatory role of Ste7 in the growth, conidiation, virulence, and/or stress tolerance of B. bassiana and perhaps other filamentous fungi.

Significant and unique changes in phosphorylation levels of four phosphoproteins in two apple rootstock genotypes under drought stress

Drought stress is a major problem around the world and there is still little molecular mechanism about how fruit crops deal with moderate drought stress. Here, the physiological and phosphoproteomic responses of drought-sensitive genotype (M26) and drought-tolerant genotype (MBB) under moderate drought stress were investigated. Our results of the physiology analysis indicated that the MBB genotype could produce more osmosis-regulating substances. Furthermore, phosphoproteins from leaves of both genotypes under moderate drought stress were analyzed using the isobaric tags for relative and absolute quantification technology. A total of 595 unique phosphopeptides, 682 phosphorylated sites, and 446 phosphoproteins were quantitatively analyzed in the two genotypes. Five and thirty-five phosphoproteins with the phosphorylation levels significantly changed (PLSC) were identified in M26 and MBB, respectively. Among these, four PLSC phosphoproteins were common to both genotypes, perhaps indicating a partial overlap of the mechanisms to moderate drought stress. Gene ontology analyses revealed that the PLSC phosphoproteins represent a unique combination of metabolism, transcription, translation, and protein processing, suggesting that the response in apple to moderate drought stress encompasses a new and unique homeostasis of major cellular processes. The basic trend was an increase in protein and organic molecules abundance related to drought. These increases were higher in MBB than in M26. Our study is the first to address the phosphoproteome of apple rootstocks in response to moderate drought stress, and provide insights into the molecular regulation mechanisms of apple rootstock under moderate drought stress.

Male gametophyte development and function in angiosperms: a general concept

Overview of pollen development. Male gametophyte development of angiosperms is a complex process that requires coordinated activity of different cell types and tissues of both gametophytic and sporophytic origin and the appropriate specific gene expression. Pollen ontogeny is also an excellent model for the dissection of cellular networks that control cell growth, polarity, cellular differentiation and cell signaling. This article describes two sequential phases of angiosperm pollen ontogenesis-developmental phase leading to the formation of mature pollen grains, and a functional or progamic phase, beginning with the impact of the grains on the stigma surface and ending at double fertilization. Here we present an overview of important cellular processes in pollen development and explosive pollen tube growth stressing the importance of reserves accumulation and mobilization and also the mutual activation of pollen tube and pistil tissues, pollen tube guidance and the communication between male and female gametophytes. We further describe the recent advances in regulatory mechanisms involved such as posttranscriptional regulation (including mass transcript storage) and posttranslational modifications to modulate protein function, intracellular metabolic signaling, ionic gradients such as Ca(2+) and H(+) ions, cell wall synthesis, protein secretion and intercellular signaling within the reproductive tissues.

Phosphoproteomic analysis of induced resistance reveals activation of signal transduction processes by beneficial and pathogenic interaction in grapevine

Protein phosphorylation regulates several key processes of the plant immune system. Protein kinases and phosphatases are pivotal regulators of defense mechanisms elicited by resistance inducers. However, the phosphorylation cascades that trigger the induced resistance mechanisms in plants have not yet been deeply investigated. The beneficial fungus Trichoderma harzianum T39 (T39) induces resistance against grapevine downy mildew (Plasmopara viticola), but its efficacy could be further improved by a better understanding of the cellular regulations involved. We investigated quantitative changes in the grapevine phosphoproteome during T39-induced resistance to get an overview of regulatory mechanisms of downy mildew resistance. Immunodetection experiments revealed activation of the 45 and 49kDa kinases by T39 treatment both before and after pathogen inoculation, and the phosphoproteomic analysis identified 103 phosphopeptides that were significantly affected by the phosphorylation cascades during T39-induced resistance. Peptides affected by T39 treatment showed comparable phosphorylation levels after P. viticola inoculation, indicating activation of the microbial recognition machinery before pathogen infection. Phosphorylation profiles of proteins related to photosynthetic processes and protein ubiquitination indicated a partial overlap of cellular responses in T39-treated and control plants. However, phosphorylation changes of proteins involved in response to stimuli, signal transduction, hormone signaling, gene expression regulation, and RNA metabolism were exclusively elicited by P. viticola inoculation in T39-treated plants. These results highlighted the relevance of phosphorylation changes during T39-induced resistance and identified key regulator candidates of the grapevine defense against downy mildew.

Data set from the phosphoproteomic analysis of Magnaporthe oryzae-responsive proteins in susceptible and resistant rice cultivars

Rice blast, caused by the fungal pathogen Magnaporthe oryzae, is the most destructive disease of rice and causes tremendous losses of rice yield worldwide. To explore the molecular mechanisms involved in the rice–M. oryzae interaction, we conducted a time-course phosphoproteomic analysis of leaf samples from resistant and susceptible rice cultivars infected with M. oryzae. This data article contains additional results and analysis of M. oryzae-regulated phosphoproteins in rice leaves [1]. We report the analysis of M. oryzae-regulated phosphoproteins at all time points, including Venn diagram analysis, close-up views, relative intensities, and functional category, and the MS spectra of representative phosphoprotein and representative phosphorylated peptides.