A cyclic nucleotide-gated channel mediates cytoplasmic calcium elevation and disease resistance in rice

The VAMP-associated protein VAP27-1 plays a crucial role in plant resistance to ER stress by modulating ER-PM contact architecture in Arabidopsis

The endoplasmic reticulum (ER) and the plasma membrane (PM) form ER-PM contact sites (EPCSs) that allow the ER and PM to exchange materials and information. Stress-induced disruption of protein folding triggers ER stress, and the cell initiates the unfolded protein response (UPR) to resist the stress. However, whether EPCSs play a role in ER stress in plants remains unclear. VESICLE-ASSOCIATED MEMBRANE PROTEIN (VAMP)-ASSOCIATED PROTEIN 27-1 (VAP27-1) functions in EPCS tethering and is encoded by a family of 10 genes (VAP27-1-10) in Arabidopsis thaliana. Here, we used CRISPR-Cas9-mediated genome editing to obtain a homozygous vap27-1 vap27-3 vap27-4 (vap27-1/3/4) triple mutant lacking three of the key VAP27 family members in Arabidopsis. The vap27-1/3/4 mutant exhibits defects in ER-PM connectivity and EPCS architecture, as well as excessive UPR signaling. We further showed that relocation of VAP27-1 to the PM mediates specific VAP27-1-related EPCS remodeling and expansion under ER stress. Moreover, the spatiotemporal dynamics of VAP27-1 at the PM increase ER-PM connectivity and enhance Arabidopsis resistance to ER stress. In addition, we revealed an important role for intracellular calcium homeostasis in the regulation of UPR signaling. Taken together, these results broaden our understanding of the molecular and cellular mechanisms of ER stress and UPR signaling in plants, providing additional clues for improving plant broad-spectrum resistance to different stresses.

Receptor-like cytoplasmic kinases: orchestrating plant cellular communication

The receptor-like kinase (RLK) family of receptors and the associated receptor-like cytoplasmic kinases (RLCKs) have expanded in plants because of selective pressure from environmental stress and evolving pathogens. RLCKs link pathogen perception to activation of coping mechanisms. RLK-RLCK modules regulate hormone synthesis and responses, reactive oxygen species (ROS) production, Ca2+ signaling, activation of mitogen-activated protein kinase (MAPK), and immune gene expression, all of which contribute to immunity. Some RLCKs integrate responses from multiple receptors recognizing distinct ligands. RLKs/RLCKs and nucleotide-binding domain, leucine-rich repeats (NLRs) were found to synergize, demonstrating the intertwined genetic network in plant immunity. Studies in arabidopsis (Arabidopsis thaliana) have provided paradigms about RLCK functions, but a lack of understanding of crop RLCKs undermines their application. In this review, we summarize current understanding of the diverse functions of RLCKs, based on model systems and observations in crop species, and the emerging role of RLCKs in pathogen and abiotic stress response signaling.

OsSRF8 interacts with OsINP1 and OsDAF1 to regulate pollen aperture formation in rice

In higher plants, mature male gametophytes have distinct apertures. After pollination, pollen grains germinate, and a pollen tube grows from the aperture to deliver sperm cells to the embryo sac, completing fertilization. In rice, the pollen aperture has a single-pore structure with a collar-like annulus and a plug-like operculum. A crucial step in aperture development is the formation of aperture plasma membrane protrusion (APMP) at the distal polar region of the microspore during the late tetrad stage. Previous studies identified OsINP1 and OsDAF1 as essential regulators of APMP and pollen aperture formation in rice, but their precise molecular mechanisms remain unclear. We demonstrate that the Poaceae-specific OsSRF8 gene, encoding a STRUBBELIG-receptor family 8 protein, is essential for pollen aperture formation in Oryza sativa. Mutants lacking functional OsSRF8 exhibit defects in APMP and pollen aperture formation, like loss-of-function OsINP1 mutants. OsSRF8 is specifically expressed during early anther development and initially diffusely distributed in the microsporocytes. At the tetrad stage, OsSRF8 is recruited by OsINP1 to the pre-aperture region through direct protein-protein interaction, promoting APMP formation. The OsSRF8-OsINP1 complex then recruits OsDAF1 to the APMP site to co-regulate annulus formation. Our findings provide insights into the mechanisms controlling pollen aperture formation in cereal species.

Plant Immunity: At the Crossroads of Pathogen Perception and Defense Response

Plants are challenged by different microbial pathogens that affect their growth and productivity. However, to defend pathogen attack, plants use diverse immune responses, such as pattern-triggered immunity (PTI), effector-triggered immunity (ETI), RNA silencing and autophagy, which are intricate and regulated by diverse signaling cascades. Pattern-recognition receptors (PRRs) and nucleotide-binding leucine-rich repeat (NLR) receptors are the hallmarks of plant innate immunity because they can detect pathogen or related immunogenic signals and trigger series of immune signaling cascades at different cellular compartments. In plants, most commonly, PRRs are receptor-like kinases (RLKs) and receptor-like proteins (RLPs) that function as a first layer of inducible defense. In this review, we provide an update on how plants sense pathogens, microbe-associated molecular patterns (PAMPs or MAMPs), and effectors as a danger signals and activate different immune responses like PTI and ETI. Further, we discuss the role RNA silencing, autophagy, and systemic acquired resistance as a versatile host defense response against pathogens. We also discuss early biochemical signaling events such as calcium (Ca2+), reactive oxygen species (ROS), and hormones that trigger the activation of different plant immune responses. This review also highlights the impact of climate-driven environmental factors on host-pathogen interactions.

Optimizing nutrient transporters to enhance disease resistance in rice

Fertilizers and plant diseases contribute positively and negatively to crop production, respectively. Macro- and micronutrients provided by the soil and fertilizers are transported by various plant nutrient transporters from the soil to the roots and shoots, facilitating growth and development. However, the homeostasis of different nutrients has different effects on plant disease. This review is aimed at providing insights into the interconnected regulation between nutrient homeostasis and immune responses, and it highlights strategies to enhance disease resistance by optimal manipulation of nutrient transporters in rice. First, we highlight the essential roles of six macronutrients (nitrogen, phosphorus, potassium, sulfur, calcium, magnesium) and eight micronutrients (iron, manganese, zinc, copper, boron, molybdenum, silicon, nickel), and summarize the diverse effects of each on rice diseases. We then systematically review the molecular mechanisms of immune responses modulated by nutrient transporters and the genetic regulatory pathways that control the specific nutrient-mediated immune signaling that is regulated by the pathogens and the host plant. Finally, we discuss putative strategies for breeding disease-resistant rice by genetic engineering of nutrient transporters.

Release of a ubiquitin brake activates OsCERK1-triggered immunity in rice

Plant pattern-recognition receptors perceive microorganism-associated molecular patterns to activate immune signalling1,2. Activation of the pattern-recognition receptor kinase CERK1 is essential for immunity, but tight inhibition of receptor kinases in the absence of pathogen is crucial to prevent autoimmunity3,4. Here we find that the U-box ubiquitin E3 ligase OsCIE1 acts as a molecular brake to inhibit OsCERK1 in rice. During homeostasis, OsCIE1 ubiquitinates OsCERK1, reducing its kinase activity. In the presence of the microorganism-associated molecular pattern chitin, active OsCERK1 phosphorylates OsCIE1 and blocks its E3 ligase activity, thus releasing the brake and promoting immunity. Phosphorylation of a serine within the U-box of OsCIE1 prevents its interaction with E2 ubiquitin-conjugating enzymes and serves as a phosphorylation switch. This phosphorylation site is conserved in E3 ligases from plants to animals. Our work identifies a ligand-released brake that enables dynamic immune regulation.

Rice false smut virulence protein subverts host chitin perception and signaling at lemma and palea for floral infection

The flower-infecting fungus Ustilaginoidea virens causes rice false smut, which is a severe emerging disease threatening rice (Oryza sativa) production worldwide. False smut not only reduces yield, but more importantly produces toxins on grains, posing a great threat to food safety. U. virens invades spikelets via the gap between the 2 bracts (lemma and palea) enclosing the floret and specifically infects the stamen and pistil. Molecular mechanisms for the U. virens-rice interaction are largely unknown. Here, we demonstrate that rice flowers predominantly employ chitin-triggered immunity against U. virens in the lemma and palea, rather than in the stamen and pistil. We identify a crucial U. virens virulence factor, named UvGH18.1, which carries glycoside hydrolase activity. Mechanistically, UvGH18.1 functions by binding to and hydrolyzing immune elicitor chitin and interacting with the chitin receptor CHITIN ELICITOR BINDING PROTEIN (OsCEBiP) and co-receptor CHITIN ELICITOR RECEPTOR KINASE1 (OsCERK1) to impair their chitin-induced dimerization, suppressing host immunity exerted at the lemma and palea for gaining access to the stamen and pistil. Conversely, pretreatment on spikelets with chitin induces a defense response in the lemma and palea, promoting resistance against U. virens. Collectively, our data uncover a mechanism for a U. virens virulence factor and the critical location of the host-pathogen interaction in flowers and provide a potential strategy to control rice false smut disease.

Pathogen perception and signaling in plant immunity

Plant diseases are a constant and serious threat to agriculture and ecological biodiversity. Plants possess a sophisticated innate immunity system capable of detecting and responding to pathogen infection to prevent disease. Our understanding of this system has grown enormously over the past century. Early genetic descriptions of plant disease resistance and pathogen virulence were embodied in the gene-for-gene hypothesis, while physiological studies identified pathogen-derived elicitors that could trigger defense responses in plant cells and tissues. Molecular studies of these phenomena have now coalesced into an integrated model of plant immunity involving cell surface and intracellular detection of specific pathogen-derived molecules and proteins culminating in the induction of various cellular responses. Extracellular and intracellular receptors engage distinct signaling processes but converge on many similar outputs with substantial evidence now for integration of these pathways into interdependent networks controlling disease outcomes. Many of the molecular details of pathogen recognition and signaling processes are now known, providing opportunities for bioengineering to enhance plant protection from disease. Here we provide an overview of the current understanding of the main principles of plant immunity, with an emphasis on the key scientific milestones leading to these insights.

Effectors and environment modulating rice blast disease: from understanding to effective control

Rice blast is a highly destructive crop disease that requires the interplay of three essential factors: the virulent blast fungus, the susceptible rice plant, and favorable environmental conditions. Although previous studies have focused mainly on the pathogen and rice, recent research has shed light on the molecular mechanisms by which the blast fungus and environmental conditions regulate host resistance and contribute to blast disease outbreaks. This review summarizes significant achievements in understanding the sophisticated modulation of blast resistance by Magnaporthe oryzae effectors and the dual regulatory mechanisms by which environmental conditions influence rice resistance and virulence of the blast fungus. Furthermore, it emphasizes potential strategies for developing blast-resistant rice varieties to effectively control blast disease.

New insight into Ca2+ -permeable channel in plant immunity

Calcium ions (Ca2+ ) are crucial intracellular second messengers in eukaryotic cells. Upon pathogen perception, plants generate a transient and rapid increase in cytoplasmic Ca2+ levels, which is subsequently decoded by Ca2+ sensors and effectors to activate downstream immune responses. The elevation of cytosolic Ca2+ is commonly attributed to Ca2+ influx mediated by plasma membrane-localized Ca2+ -permeable channels. However, the contribution of Ca2+ release triggered by intracellular Ca2+ -permeable channels in shaping Ca2+ signaling associated with plant immunity remains poorly understood. This review discusses recent advances in understanding the mechanism underlying the shaping of Ca2+ signatures upon the activation of immune receptors, with particular emphasis on the identification of intracellular immune receptors as non-canonical Ca2+ -permeable channels. We also discuss the involvement of Ca2+ release from the endoplasmic reticulum in generating Ca2+ signaling during plant immunity.

Natural variation in the pattern-triggered immunity response in plants: Investigations, implications and applications

The pattern-triggered immunity (PTI) response is triggered at the plant cell surface by the recognition of microbe-derived molecules known as microbe- or pathogen-associated molecular patterns or molecules derived from compromised host cells called damage-associated molecular patterns. Membrane-localized receptor proteins, known as pattern recognition receptors, are responsible for this recognition. Although much of the machinery of PTI is conserved, natural variation for the PTI response exists within and across species with respect to the components responsible for pattern recognition, activation of the response, and the strength of the response induced. This review describes what is known about this variation. We discuss how variation in the PTI response can be measured and how this knowledge might be utilized in the control of plant disease and in developing plant varieties with enhanced disease resistance.

Long small RNA76113 targets CYCLIC NUCLEOTIDE-GATED ION CHANNEL 5 to repress disease resistance in rice

Small RNAs are widely involved in plant immune responses. However, the role of long small RNAs (25 to 40 nt) in monocot plant disease resistance is largely unknown. Here, we identified a long small RNA (lsiR76113) from rice (Oryza sativa) that is downregulated by Magnaporthe oryzae infection and targets a gene encoding CYCLIC NUCLEOTIDE-GATED CHANNEL 5 (CNGC5). The cngc5 mutant lines were more susceptible to M. oryzae than the wild type, while knocking down lsiR76113 in transgenic rice plants promoted pathogen resistance. A protoplast transient expression assay showed that OsCNGC5 promotes Ca2+ influx. These results demonstrate that OsCNGC5 enhances rice resistance to rice blast by increasing the cytosolic Ca2+ concentration. Importantly, exogenous Ca2+ application enhanced rice M. oryzae resistance by affecting reactive oxygen species (ROS) production. Moreover, cngc5 mutants attenuated the PAMP-triggered immunity response, including chitin-induced and flg22-induced ROS bursts and protein phosphorylation in the mitogen-activated protein kinase cascade, indicating that OsCNGC5 is essential for PAMP-induced calcium signaling in rice. Taken together, these results suggest that lsiR76113-mediated regulation of Ca2+ influx is important for PTI responses and disease resistance in rice.

Receptor-like kinases OsRLK902-1 and OsRLK902-2 form immune complexes with OsRLCK185 to regulate rice blast resistance

Receptor-like kinases (RLKs) are major regulators of the plant immune response and play important roles in the perception and transmission of immune signals. RECEPTOR LIKE KINASE 902 (RLK902) is at the key node in leucine-rich repeat receptor-like kinase interaction networks and positively regulates resistance to the bacterial pathogen Pseudomonas syringae in Arabidopsis. However, the function of RLK902 in fungal disease resistance remains obscure. In this study, we found that the expression levels of OsRLK902-1 and OsRLK902-2, encoding two orthologues of RLK902 in rice, were induced by Magnaporthe oryzae, chitin, and flg22 treatment. osrlk902-1 and osrlk902-2 knockout mutants displayed enhanced susceptibility to M. oryzae. Interestingly, the osrlk902-1 rlk902-2 double mutant exhibited similar disease susceptibility, hydrogen peroxide production, and callose deposition to the two single mutants. Further investigation showed that OsRLK902-1 interacts with and stabilizes OsRLK902-2. The two OsRLKs form a complex with OsRLCK185, a key regulator in chitin-triggered immunity, and stabilize it. Taken together, our data demonstrate that OsRLK902-1 and OsRLK902-2, as well as OsRLCK185 function together in regulating disease resistance to M. oryzae in rice.

Rice NLR protein XinN1, induced by a pattern recognition receptor XA21, confers enhanced resistance to bacterial blight

KEY MESSAGE

Rice CC-type NLR XinN1, specifically induced by a PRR XA21, activates defense pathways against Xoo. Plants have evolved two layers of immune systems regulated by two different types of immune receptors, cell surface located pattern recognition receptors (PRRs) and intracellular nucleotide-binding domain leucine-rich repeat-containing receptors (NLRs). Plant PRRs recognize conserved molecular patterns from diverse pathogens, resulting in pattern-triggered immunity (PTI), whereas NLRs are activated by effectors secreted by pathogens into plant cells, inducing effector-triggered immunity (ETI). Rice PRR, XA21, recognizes a tyrosine-sulfated RaxX peptide (required for activation of XA21-mediated immunity X) as a molecular pattern secreted by Xanthomonas oryzae pv. oryzae (Xoo). Here, we identified a rice NLR gene, XinN1, that is specifically induced during the XA21-mediated immune response against Xoo. Transgenic rice plants overexpressing XinN1 displayed increased resistance to infection by Xoo with reduced lesion length and bacterial growth. Overexpression of autoactive mutant of XinN1 (XinN1D543V) also displayed increased resistance to Xoo, accompanied with severe growth retardation and cell death. In rice protoplast system, overexpression of XinN1 or XinN1D543V significantly elevated reactive oxygen species (ROS) production and cytosolic-free calcium (Ca2+) accumulations. In addition, XinN1 overexpression additionally elevated the ROS burst caused by the interaction between XA21 and RaxX-sY and induced the transcription of PTI signaling components, including somatic embryogenesis receptor kinases (OsSERKs) and receptor-like cytoplasmic kinases (OsRLCKs). Our results suggest that XinN1 induced by the PRR XA21 activates defense pathways and provides enhanced resistance to Xoo in rice.

OsLRR-RLP2 Gene Regulates Immunity to Magnaporthe oryzae in Japonica Rice

Rice is an important cereal crop worldwide, the growth of which is affected by rice blast disease, caused by the fungal pathogen Magnaporthe oryzae. As climate change increases the diversity of pathogens, the disease resistance genes (R genes) in plants must be identified. The major blast-resistance genes have been identified in indica rice varieties; therefore, japonica rice varieties with R genes now need to be identified. Because leucine-rich repeat (LRR) domain proteins possess R-gene properties, we used bioinformatics analysis to identify the rice candidate LRR domain receptor-like proteins (OsLRR-RLPs). OsLRR-RLP2, which contains six LRR domains, showed differences in the DNA sequence, containing 43 single-nucleotide polymorphisms (SNPs) in indica and japonica subpopulations. The results of the M. oryzae inoculation analysis indicated that indica varieties with partial deletion of OsLRR-RLP2 showed susceptibility, whereas japonica varieties with intact OsLRR-RLP2 showed resistance. The oslrr-rlp2 mutant, generated using clustered regularly interspaced palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9), showed increased pathogen susceptibility, whereas plants overexpressing this gene showed pathogen resistance. These results indicate that OsLRR-RLP2 confers resistance to rice, and OsLRR-RLP2 may be useful for breeding resistant cultivars.

Calcium homeostasis and signaling in plant immunity

Calcium (Ca2+) signaling consists of three steps: (1) initiation of a change in cellular Ca2+ concentration in response to a stimulus, (2) recognition of the change through direct binding of Ca2+ by its sensors, (3) transduction of the signal to elicit downstream responses. Recent studies have uncovered a central role for Ca2+ signaling in both layers of immune responses initiated by plasma membrane (PM) and intracellular receptors, respectively. These advances in our understanding are attributed to several lines of research, including invention of genetically-encoded Ca2+ reporters for the recording of intracellular Ca2+ signals, identification of Ca2+ channels and their gating mechanisms, and functional analysis of Ca2+ binding proteins (Ca2+ sensors). This review analyzes the recent literature that illustrates the importance of Ca2+ homeostasis and signaling in plant innate immunity, featuring intricate Ca2+dependent positive and negative regulations.

Knockout of a rice K5.2 gene increases Ca accumulation in the grain

Rice is a staple food for half of the world's population, but it is a poor dietary source of calcium (Ca) due to the low concentration. It is an important issue to boost Ca concentration in this grain to improve Ca deficiency risk, but the mechanisms underlying Ca accumulation are poorly understood. Here, we obtained a rice (Oryza sativa) mutant with high shoot Ca accumulation. The mutant exhibited 26%-53% higher Ca in shoots than did wild-type rice (WT) at different Ca supplies. Ca concentration in the xylem sap was 36% higher in the mutant than in the WT. There was no difference in agronomic traits between the WT and mutant, but the mutant showed 25% higher Ca in the polished grain compared with the WT. Map-based cloning combined with a complementation test revealed that the mutant phenotype was caused by an 18-bp deletion of a gene, OsK5.2, belonging to the Shaker-like K+ channel family. OsK5.2 was highly expressed in the mature region of the roots and its expression in the roots was not affected by Ca levels, but upregulated by low K. Immunostaining showed that OsK5.2 was mainly expressed in the pericycle of the roots. Taken together, our results revealed a novel role for OsK5.2 in Ca translocation in rice, and will be a good target for Ca biofortification in rice.

Oomycete effector AVRblb2 targets cyclic nucleotide-gated channels through calcium sensors to suppress pattern-triggered immunity

Transient and rapid increase in cytosolic Ca2+ plays a crucial role in plant-pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI). Cyclic nucleotide-gated channels (CNGCs) have been implicated in mediating this Ca2+ influx; however, their regulatory mechanisms remain poorly understood. Here, we have found that AVRblb2 requires the calmodulin (CaM) and calmodulin-like (CML) proteins as co-factors to interact with the NbCNGCs, resulting in the formation of AVRblb2-CaM/CML-NbCNGCs complex. Furthermore, CaM and CML are dissociated from NbCNGC18 during PTI response to increase Ca2+ influx; however, Avrblb2 inhibits calcium channel activation by disrupting the release of CaM and CML from NbCNGC18. Following recognition of PAMP, NbCNGC18 forms active heteromeric channels with other NbCNGCs, which may give selectivity of CNGC complex against diverse signals for fine-tuning of cytosolic Ca2+ level to mediate appropriate responses. Silencing of multiple NbCNGCs compromised the function of AVRblb2 on the pathogenicity of Phytophthora infestans, confirming that AVRblb2 contributes to pathogen virulence by targeting CNGCs. Our findings provide new insights into the regulation of CNGCs in PTI and the role of pathogen effectors in manipulating host cell physiology to promote infection.

Identification of the CNGC Gene Family in Rice and Mining of Alleles for Application in Rice Improvement

Cyclic nucleotide-gated ion channel (CNGC) gene regulation plays important roles in plant immune and abiotic stress response. Here, we identified 16 CNGC genes in rice (Oryza sativa). Then, we analyzed their chromosomal location, physicochemical properties, subcellular localization, gene functional interaction network, cis-acting elements, phylogenetic relationships, collinearity, expression in tissues under normal conditions and abiotic stresses, and geng-cds-haplotype (gcHap) diversity in 3010 gcHaps. As a result, OsCNGC3 (Os06g0527300) was identified as a gene different from previous report, and OsCNGC genes were found to play important roles in rice population differentiation and rice improvement. Our results revealed their very strong differentiation between subspecies and populations, important roles in response to abiotic stresses, as well as strong genetic bottleneck effects and artificial selection of gcHap diversity in the modern breeding process of Xian (indica) and Geng (japonica) populations. The results also suggested that natural variations in most rice CNGC loci are potentially valuable for improving rice productivity and tolerance to abiotic stresses. The favorable alleles at the CNGC loci should be explored to facilitate their application in future rice improvement.

The herbicide bensulfuron-methyl inhibits rice seedling development by blocking calcium ion flux in the OsCNGC12 channel

Identification of translocator protein-related genes involved in bensulfuron-methyl (BSM) uptake and transport in rice could facilitate the development of herbicide-tolerant cultivars by inactivating them. This study found that the OsCNGC12 mutants not only reduced BSM uptake but also compromised the Ca2 ⁺ efflux caused by BSM in the roots, regulating dynamic equilibrium of Ca2 ⁺ inside the cell and conferring non-target-site tolerance to BSM.

LysM Proteins TaCEBiP and TaLYK5 are Involved in Immune Responses Mediated by Chitin Coreceptor TaCERK1 in Wheat

Plant lysin motif (LysM) ectodomain receptors interact with pathogen-associated molecular patterns (PAMPs) and have critical functions in plant-microbe interactions. In this study, 65 LysM family genes were identified using the recent version of the reference sequence of bread wheat (Triticum aestivum), in which 23, 16, 20, and 6 members belonged to LysM-containing receptor-like kinases (LYKs), LysM-containing receptor-like proteins (LYPs), extracellular LysM proteins (LysMes), and intracellular nonsecretory LysM proteins (LysMns), respectively. The study found that TaCEBiP, TaLYK5, and TaCERK1 were highly responsive to PAMP elicitors and phytopathogens, with TaCEBiP and TaLYK5 binding directly to chitin. TaCERK1 acted as a coreceptor with TaCEBiP and TaLYK5 at the plasma membrane. Overexpression of TaCEBiP, TaLYK5, and TaCERK1 in Nicotiana benthamiana leaves exhibited enhanced resistance to Sclerotinia sclerotiorum. Subsequently, knocking down TaCEBiP, TaLYK5, and TaCERK1 genes with barley stripe mosaic virus-VIGS compromised the wheat defense response to an avirulent strain of Puccinia striiformis. The study concluded that wheat has two synergistic chitin perception systems for detecting pathogen elicitors, with the activated CERK1 intracellular kinase domain leading to signaling transduction. This research provides valuable insights into the functional roles and regulatory mechanisms of wheat LysM members under biotic stress.

Early and Late Transcriptomic and Metabolomic Responses of Rhododendron 'Xiaotaohong' Petals to Infection with Alternaria sp

In recent years, petal blight disease caused by pathogens has become increasingly epidemic in Rhododendron. Breeding disease-resistant rhododendron is considered to be a more environmentally friendly strategy than is the use of chemical reagents. In this study, we aimed to investigate the response mechanisms of rhododendron varieties to petal blight, using transcriptomics and metabolomics analyses. Specifically, we monitored changes in gene expression and metabolite accumulation in Rhododendron 'Xiaotaohong' petals infected with the Alternaria sp. strain (MR-9). The infection of MR-9 led to the development of petal blight and induced significant changes in gene transcription. Differentially expressed genes (DEGs) were predominantly enriched in the plant-pathogen interaction pathway. These DEGs were involved in carrying out stress responses, with genes associated with H2O2 production being up-regulated during the early and late stages of infection. Correspondingly, H2O2 accumulation was detected in the vicinity of the blight lesions. In addition, defense-related genes, including PR and FRK, exhibited significant up-regulated expression during the infection by MR-9. In the late stage of the infection, we also observed significant changes in differentially abundant metabolites (DAMs), including flavonoids, alkaloids, phenols, and terpenes. Notably, the levels of euscaphic acid, ganoderol A, (-)-cinchonidine, and theophylline in infected petals were 21.8, 8.5, 4.5, and 4.3 times higher, respectively, compared to the control. Our results suggest that H2O2, defense-related genes, and DAM accumulation are involved in the complex response mechanisms of Rhododendron 'Xiaotaohong' petals to MR-9 infection. These insights provide a deeper understanding of the pathogenesis of petal blight disease and may have practical implications for developing disease-resistant rhododendron varieties.

Multiomics analysis reveals the molecular mechanisms underlying virulence in Rhizoctonia and jasmonic acid-mediated resistance in Tartary buckwheat (Fagopyrum tataricum)

Rhizoctonia solani is a devastating soil-borne pathogen that seriously threatens the cultivation of economically important crops. Multiple strains with a very broad host range have been identified, but only 1 (AG1-IA, which causes rice sheath blight disease) has been examined in detail. Here, we analyzed AG4-HGI 3 originally isolated from Tartary buckwheat (Fagopyrum tataricum), but with a host range comparable to AG1-IA. Genome comparison reveals abundant pathogenicity genes in this strain. We used multiomic approaches to improve the efficiency of screening for disease resistance genes. Transcriptomes of the plant-fungi interaction identified differentially expressed genes associated with virulence in Rhizoctonia and resistance in Tartary buckwheat. Integration with jasmonate-mediated transcriptome and metabolome changes revealed a negative regulator of jasmonate signaling, cytochrome P450 (FtCYP94C1), as increasing disease resistance probably via accumulation of resistance-related flavonoids. The integration of resistance data for 320 Tartary buckwheat accessions identified a gene homolog to aspartic proteinase (FtASP), with peak expression following R. solani inoculation. FtASP exhibits no proteinase activity but functions as an antibacterial peptide that slows fungal growth. This work reveals a potential mechanism behind pathogen virulence and host resistance, which should accelerate the molecular breeding of resistant varieties in economically essential crops.

The emerging frontier of plant immunity's core hubs

The ever-growing world population, increasingly frequent extreme weather events and conditions, emergence of novel devastating crop pathogens and the social strive for quality food products represent a huge challenge for current and future agricultural production systems. To address these challenges and find realistic solutions, it is becoming more important by the day to understand the complex interactions between plants and the environment, mainly the associated organisms, but in particular pathogens. In the past several years, research in the fields of plant pathology and plant-microbe interactions has enabled tremendous progress in understanding how certain receptor-based plant innate immune systems function to successfully prevent infections and diseases. In this review, we highlight and discuss some of these new ground-breaking discoveries and point out strategies of how pathogens counteract the function of important core convergence hubs of the plant immune system. For practical reasons, we specifically place emphasis on potential applications that can be detracted by such discoveries and what challenges the future of agriculture has to face, but also how these challenges could be tackled.

WeiTsing, a pericycle-expressed ion channel, safeguards the stele to confer clubroot resistance

Plant roots encounter numerous pathogenic microbes that often cause devastating diseases. One such pathogen, Plasmodiophora brassicae (Pb), causes clubroot disease and severe yield losses on cruciferous crops worldwide. Here, we report the isolation and characterization of WeiTsing (WTS), a broad-spectrum clubroot resistance gene from Arabidopsis. WTS is transcriptionally activated in the pericycle upon Pb infection to prevent pathogen colonization in the stele. Brassica napus carrying the WTS transgene displayed strong resistance to Pb. WTS encodes a small protein localized in the endoplasmic reticulum (ER), and its expression in plants induces immune responses. The cryoelectron microscopy (cryo-EM) structure of WTS revealed a previously unknown pentameric architecture with a central pore. Electrophysiology analyses demonstrated that WTS is a calcium-permeable cation-selective channel. Structure-guided mutagenesis indicated that channel activity is strictly required for triggering defenses. The findings uncover an ion channel analogous to resistosomes that triggers immune signaling in the pericycle.

TIR-catalyzed nucleotide signaling molecules in plant defense

Toll and interleukin-1 receptor (TIR) domain is a conserved immune module in prokaryotes and eukaryotes. Signaling regulated by TIR-only proteins or TIR domain-containing intracellular immune receptors is critical for plant immunity. Recent studies demonstrated that TIR domains function as enzymes encoding a variety of activities, which manifest different mechanisms for regulation of plant immunity. These enzymatic activities catalyze metabolism of NAD+, ATP and other nucleic acids, generating structurally diversified nucleotide metabolites. Signaling roles have been revealed for some TIR enzymatic products that can act as second messengers to induce plant immunity. Herein, we summarize our current knowledge about catalytic production of these nucleotide metabolites and their roles in plant immune signaling. We also highlight outstanding questions that are likely to be the focus of future investigations about TIR-produced signaling molecules.

A phospho-switch constrains BTL2-mediated phytocytokine signaling in plant immunity

Enabling and constraining immune activation is of fundamental importance in maintaining cellular homeostasis. Depleting BAK1 and SERK4, the co-receptors of multiple pattern recognition receptors (PRRs), abolishes pattern-triggered immunity but triggers intracellular NOD-like receptor (NLR)-mediated autoimmunity with an elusive mechanism. By deploying RNAi-based genetic screens in Arabidopsis, we identified BAK-TO-LIFE 2 (BTL2), an uncharacterized receptor kinase, sensing BAK1/SERK4 integrity. BTL2 induces autoimmunity through activating Ca2+ channel CNGC20 in a kinase-dependent manner when BAK1/SERK4 are perturbed. To compensate for BAK1 deficiency, BTL2 complexes with multiple phytocytokine receptors, leading to potent phytocytokine responses mediated by helper NLR ADR1 family immune receptors, suggesting phytocytokine signaling as a molecular link connecting PRR- and NLR-mediated immunity. Remarkably, BAK1 constrains BTL2 activation via specific phosphorylation to maintain cellular integrity. Thus, BTL2 serves as a surveillance rheostat sensing the perturbation of BAK1/SERK4 immune co-receptors in promoting NLR-mediated phytocytokine signaling to ensure plant immunity.

Genome-wide identification and expression analysis of the cyclic nucleotide-gated ion channel (CNGC) gene family in Saccharum spontaneum

BACKGROUND

Cyclic nucleotide-gated ion channels (CNGCs) are nonselective cation channels that are ubiquitous in eukaryotic organisms. As Ca²⁺ channels, some CNGCs have also proven to be K⁺-permeable and involved in plant development and responses to environmental stimuli. Sugarcane is an important sugar and energy crop worldwide. However, reports on CNGC genes in sugarcane are limited.

RESULTS

In this study, 16 CNGC genes and their alleles were identified from Saccharum spontaneum and classified into 5 groups based on phylogenetic analysis. Investigation of gene duplication and syntenic relationships between S. spontaneum and both rice and Arabidopsis demonstrated that the CNGC gene family in S. spontaneum expanded primarily by segmental duplication events. Many SsCNGCs showed variable expression during growth and development as well as in tissues, suggesting functional divergence. Light-responsive cis-acting elements were discovered in the promoters of all the identified SsCNGCs, and the expression of most of the SsCNGCs showed a diurnal rhythm. In sugarcane, the expression of some SsCNGCs was regulated by low-K⁺ treatment. Notably, SsCNGC13 may be involved in both sugarcane development and its response to environmental stimuli, including response to low-K⁺ stress.

CONCLUSION

This study identified the CNGC genes in S. spontaneum and provided insights into the transcriptional regulation of these SsCNGCs during development, circadian rhythm and under low-K⁺ stress. These findings lay a theoretical foundation for future investigations of the CNGC gene family in sugarcane.

An OsPRMT5-OsAGO2/miR1875-OsHXK1 module regulates rice immunity to blast disease

Rice ARGONAUTE2 (OsAGO2) is a core component of the rice RNA-induced silencing complex (RISC), which is repressed by Magnaporthe oryzae (M. oryzae) infection. Whether and how OsAGO2-mediated gene silencing plays a role in rice blast resistance and which sRNAs participate in this process are unknown. Our results indicate that OsAGO2 is a key immune player that manipulates rice defense responses against blast disease. OsAGO2 associates with the 24-nt miR1875 and binds to the promoter region of HEXOKINASE1 (OsHXK1), which causes DNA methylation and leads to gene silencing. Our multiple genetic evidence showed that, without M. oryzae infection, OsAGO2/miR1875 RISC promoted OsHXK1 promoter DNA methylation and OsHXK1 silencing; after M. oryzae infection, the reduced OsAGO2/miR1875 led to a relatively activated OsHXK1 expression. OsHXK1 acts as a positive regulator of blast disease resistance that OsHXK1-OE rice exhibited enhanced resistance, whereas Cas9-Oshxk1 rice showed reduced resistance against M. oryzae infection. OsHXK1 may function through its sugar sensor activity as glucose induced defense-related gene expression and reactive oxygen species (ROS) accumulation in Nipponbare and OsHXK1-OE but not in Cas9-Oshxk1 rice. OsAGO2 itself is delicately regulated by OsPRMT5, which senses M. oryzae infection and attenuates OsAGO2-mediated gene silencing through OsAGO2 arginine methylation. Our study reveals an OsPRMT5-OsAGO2/miR1875-OsHXK1 regulatory module that fine tunes the rice defense response to blast disease.

Identification of CNGCs in Glycine max and Screening of Related Resistance Genes after Fusarium solani Infection

Cyclic nucleotide-gated channels (CNGCs), non-selective cation channels localised on the plasmalemma, are involved in growth, development, and regulatory mechanisms in plants during adverse stress. To date, CNGC gene families in multiple crops have been identified and analysed. However, there have been no systematic studies on the evolution and development of CNGC gene families in legumes. Therefore, in the present study, via transcriptome analysis, we identified 143 CNGC genes in legumes, and thereafter, classified and named them according to the grouping method used for Arabidopsis thaliana. Functional verification for disease stress showed that four GmCNGCs were specifically expressed in the plasmalemma during the stress process. Further, functional enrichment analysis showed that their mode of participation and coordination included inorganic ion concentration regulation inside and outside the membrane via the transmembrane ion channel and participation in stress regulation via signal transduction. The CNGC family genes in G. max involved in disease stress were also identified and physiological stress response and omics analyses were also performed. Our preliminary results revealed the basic laws governing the involvement of CNGCs in disease resistance in G. max, providing important gene resources and a theoretical reference for the breeding of resistant soybean.

Isolation and Characterization of SPOTTED LEAF42 Encoding a Porphobilinogen Deaminase in Rice

The formation and development of chloroplasts play a vital role in the breeding of high-yield rice (Oryza sativa L.). Porphobilinogen deaminases (PBGDs) act in the early stage of chlorophyll and heme biosynthesis. However, the role of PBGDs in chloroplast development and chlorophyll production remains elusive in rice. Here, we identified the spotted leaf 42 (spl42) mutant, which exhibited a reddish-brown spotted leaf phenotype. The mutant showed a significantly lower chlorophyll content, abnormal thylakoid morphology, and elevated activities of reactive oxygen species (ROS)-scavenging enzymes. Consistently, multiple genes related to chloroplast development and chlorophyll biosynthesis were significantly down-regulated, whereas many genes involved in leaf senescence, ROS production, and defense responses were upregulated in the spl42 mutant. Map-based cloning revealed that SPL42 encodes a PBGD. A C-to-T base substitution occurred in spl42, resulting in an amino acid change and significantly reduced PBGD enzyme activity. SPL42 targets to the chloroplast and interacts with the multiple organelle RNA editing factors (MORFs) OsMORF8-1 and OsMORF8-2 to affect RNA editing. The identification and characterization of spl42 helps in elucidating the molecular mechanisms associated with chlorophyll synthesis and RNA editing in rice.

Transcriptome analysis reveals the regulation of cyclic nucleotide-gated ion channels in response to exogenous abscisic acid and calcium treatment under drought stress in tomato

Background: Drought stress can limit the growth and development of tomato seedlings and cause considerable loss of tomato yield. Exogenous abscisic acid (ABA) and calcium (Ca²⁺) can effectively alleviate the damage of drought stress to plants in part because Ca²⁺ acts as a second messenger in the drought resistance pathway. Although cyclic nucleotide-gated ion channels (CNGCs) are common non-specific Ca²⁺ osmotic channels in cell membranes, a thorough understanding of the transcriptome characteristics of tomato treated with exogenous ABA and Ca²⁺ under drought stress is necessary to characterize the molecular mechanism of CNGC involved in tomato drought resistance. Results: There were 12,896 differentially expressed genes in tomato under drought stress, as well as 11,406 and 12,502 differentially expressed genes after exogenous ABA and Ca²⁺ application, respectively. According to functional annotations and reports, the 19 SlCNGC genes related to Ca²⁺ transport were initially screened, with 11 SlCNGC genes that were upregulated under drought stress and downregulated after exogenous ABA application. After exogenous Ca²⁺ application, the data showed that two of these genes were upregulated, while nine genes were downregulated. Based on these expression patterns, we predicted the role of SlCNGC genes in the drought resistance pathway and their regulation by exogenous ABA and Ca²⁺ in tomato. Conclusion: The results of this study provide foundational data for further study of the function of SlCNGC genes and a more comprehensive understanding of drought resistance mechanisms in tomato.

RALF signaling pathway activates MLO calcium channels to maintain pollen tube integrity

Pollen tube tip growth requires intricate Ca²⁺ signaling. Recent studies have also identified rapid alkalization factor (RALF)-family peptides and their receptors as critical components for pollen tube tip growth and integrity. The functional relationship of RALF and calcium signaling modules remains largely unclear. Here we report that disruption of RALF signaling pathway abolished the cytosolic Ca²⁺ gradient in the pollen tube, indicating that Ca²⁺ signaling is downstream of the RALF signaling pathway. We identified MILDEW RESISTANCE LOCUS O (MLO) family proteins MLO1, 5, 9, 15, as Ca²⁺ channels required for Ca²⁺ influx and pollen tube integrity. We further reconstituted the biochemical pathway in which signaling via RALF and RALF receptors activated MLO1/5/9/15 calcium channels. Together, we conclude that RALF peptides derived from pollen tube bind to their receptors to establish pollen tube Ca²⁺ gradient through activation of the MLO channels. Our finding has thus provided a mechanistic link between the RALF signaling pathway and Ca²⁺ signaling in controlling pollen tube integrity and growth.

Calcium signaling in plant immunity: a spatiotemporally controlled symphony

Calcium ions (Ca²⁺) are prominent intracellular messengers in all eukaryotic cells. Recent studies have emphasized the crucial roles of Ca²⁺ in plant immunity. Here, we review the latest progress on the spatiotemporal control of Ca²⁺ function in plant immunity. We discuss discoveries of how Ca²⁺ influx is triggered upon the activation of immune receptors, how Ca²⁺-permeable channels are activated, how Ca²⁺ signals are decoded inside plant cells, and how these signals are switched off. Despite recent advances, many open questions remain and we highlight the existing toolkit and the new technologies to address the outstanding questions of Ca²⁺ signaling in plant immunity.

Walking through crossroads-rice responses to heat and biotic stress interactions

Rice, the most important source of calories for humans is prone to severe yield loss due to changing climate including heat stress. Additionally, rice encounters biotic stresses in conjunction with heat stress, which exacerbates the adverse effects, and exponentially increase such losses. Several investigations have identified biotic and heat stress-related quantitative trait loci (QTLs) that may contribute to improved tolerance to these stresses. However, a significant knowledge gap exists in identifying the genomic regions imparting tolerance against combined biotic and heat stress. Hereby, we are presenting a conceptual meta-analysis identifying genomic regions that may be promising candidates for enhancing combined biotic and heat stress tolerance in rice. Fourteen common genomic regions were identified along chromosomes 1, 2, 3, 4, 6, 10 and 12, which harbored 1265 genes related to heat stress and defense responses in rice. Further, the meta expression analysis revealed 24 differentially expressed genes (DEGs) involved in calcium-mediated stress signaling including transcription factors Myb, bHLH, ROS signaling, molecular chaperones HSP110 and pathogenesis related proteins. Additionally, we also proposed a hypothetical model based on GO and MapMan analysis representing the pathways intersecting heat and biotic stresses. These DEGs can be potential candidate genes for improving tolerance to combined biotic and heat stress in rice. We present a framework highlighting plausible connecting links (QTLs/genes) between rice response to heat stress and different biotic factors associated with yield, that can be extended to other crops.

The Nucleotide Revolution: Immunity at the Intersection of Toll/Interleukin-1 Receptor Domains, Nucleotides, and Ca2

The discovery of the enzymatic activity of the toll/interleukin-1 receptor (TIR) domain protein SARM1 five years ago preceded a flood of discoveries regarding the nucleotide substrates and products of TIR domains in plants, animals, bacteria, and archaea. These discoveries into the activity of TIR domains coincide with major advances in understanding the structure and mechanisms of NOD-like receptors and the mutual dependence of pattern recognition receptor- and effector-triggered immunity (PTI and ETI, respectively) in plants. It is quickly becoming clear that TIR domains and TIR-produced nucleotides are ancestral signaling molecules that modulate immunity and that their activity is closely associated with Ca²⁺ signaling. TIR domain research now bridges the separate disciplines of molecular plant- and animal-microbe interactions, neurology, and prokaryotic immunity. A cohesive framework for understanding the role of enzymatic TIR domains in diverse organisms will help unite the research of these disparate fields. Here, we review known products of TIR domains in plants, animals, bacteria, and archaea and use context gained from animal and prokaryotic TIR domain systems to present a model for TIR domains, nucleotides, and Ca²⁺ at the intersection of PTI and ETI in plant immunity. [Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

An Overview of PRR- and NLR-Mediated Immunities: Conserved Signaling Components across the Plant Kingdom That Communicate Both Pathways

Cell-surface-localized pattern recognition receptors (PRRs) and intracellular nucleotide-binding domain and leucine-rich repeat receptors (NLRs) are plant immune proteins that trigger an orchestrated downstream signaling in response to molecules of microbial origin or host plant origin. Historically, PRRs have been associated with pattern-triggered immunity (PTI), whereas NLRs have been involved with effector-triggered immunity (ETI). However, recent studies reveal that such binary distinction is far from being applicable to the real world. Although the perception of plant pathogens and the final mounting response are achieved by different means, central hubs involved in signaling are shared between PTI and ETI, blurring the zig-zag model of plant immunity. In this review, we not only summarize our current understanding of PRR- and NLR-mediated immunities in plants, but also highlight those signaling components that are evolutionarily conserved across the plant kingdom. Altogether, we attempt to offer an overview of how plants mediate and integrate the induction of the defense responses that comprise PTI and ETI, emphasizing the need for more evolutionary molecular plant-microbe interactions (EvoMPMI) studies that will pave the way to a better understanding of the emergence of the core molecular machinery involved in the so-called evolutionary arms race between plants and microbes.

Seed priming with calcium chloride enhances stress tolerance in rice seedlings

Calcium is a crucial second messenger in plant cells and contributes to plant resistance against biotic and abiotic stress. Plant defense priming with natural or synthetic compounds leads to quicker and stronger resistance responses. However, whether pretreatment of plant seeds with calcium could improve their resistance to stress remains poorly understood. In this study, we showed that rice seedlings grown from calcium chloride (CaCl₂)-pretreated seeds displayed enhanced resistance to the rice blast fungus Magnaporthe oryzae and the rice bacterial pathogen Xanthomonas oryzae pv. Oryzae (Xoo). Seed priming with CaCl₂ also led to enhanced rice tolerance to salt and cold. Furthermore, the reactive oxygen species (ROS) burst increased significantly upon immunity activation in the leaves of rice seedlings grown from CaCl₂-pretreated seeds. Additionally, we analyzed the rice calmodulin-binding protein 60 (OsCBP60) family and found that there were 19 OsCBP60s in rice cultivar Zhonghua 11 (ZH11). The transcripts of several OsCBP60s were chitin- and M. oryzae-inducible, suggesting that they may contribute to rice resistance. Taken together, these data indicate that seed priming with CaCl₂ can effectively enhance rice tolerance to multiple stresses, perhaps by boosting the burst of ROS, and OsCBP60 family members may also play an essential role in this process.

NLR we there yet? Nucleocytoplasmic coordination of NLR-mediated immunity

Plant intracellular nucleotide-binding leucine-rich repeat immune receptors (NLRs) perceive the activity of pathogen-secreted effector molecules that, when undetected, promote colonisation of hosts. Signalling from activated NLRs converges with and potentiates downstream responses from activated pattern recognition receptors (PRRs) that sense microbial signatures at the cell surface. Efficient signalling of both receptor branches relies on the host cell nucleus as an integration point for transcriptional reprogramming, and on the macromolecular transport processes that mediate the communication between cytoplasm and nucleoplasm. Studies on nuclear pore complexes (NPCs), the nucleoporin proteins (NUPs) that compose NPCs, and nuclear transport machinery constituents that control nucleocytoplasmic transport, have revealed that they play important roles in regulating plant immune responses. Here, we discuss the contributions of nucleoporins and nuclear transport receptor (NTR)-mediated signal transduction in plant immunity with an emphasis on NLR immune signalling across the nuclear compartment boundary and within the nucleus. We also highlight and discuss cytoplasmic and nuclear functions of NLRs and their signalling partners and further consider the potential implications of NLR activation and resistosome formation in both cellular compartments for mediating plant pathogen resistance and programmed host cell death.

Concerted actions of PRR- and NLR-mediated immunity

Plants utilise cell-surface immune receptors (functioning as pattern recognition receptors, PRRs) and intracellular nucleotide-binding leucine-rich repeat receptors (NLRs) to detect pathogens. Perception of pathogens by these receptors activates immune signalling and resistance to infections. PRR- and NLR-mediated immunity have primarily been considered parallel processes contributing to disease resistance. Recent studies suggest that these two pathways are interdependent and converge at multiple nodes. This review summarises and provides a perspective on these convergent points.

FERONIA-like receptor 1-mediated calcium ion homeostasis is involved in the immune response

Calcium (Ca²⁺) is the most abundant divalent cation in plants, and cellular levels of Ca²⁺, which functions as a nutrient and secondary messenger, play a critical role in plant immunity. In the present study, we found that FERONIA-like receptor 1 (FLR1) positively regulates Magnaporthe oryzae resistance and that expression of FLR1 is strongly induced in response to Ca²⁺ deficiency. In addition, the Ca content in the shoots of flr1 was lower than that in wild-type, and the M. oryzae-sensitive phenotype of the flr1 mutant was not rescued by exogenous application of Ca²⁺. Moreover, RNA sequencing revealed 2,697 differentially expressed genes (DEGs) in the flr1 mutant compared with wild-type, and some of these DEGs are involved in cellular metal ion homeostasis and transition metal ion homeostasis. Changes in expression of overlapping genes between the flr1 mutant and in plants under low-Ca²⁺ treatment were consistent in terms of direction, indicating that FLR1 is involved in Ca²⁺ homeostasis. In summary, we detected FLR1-mediated resistance to M. oryzae, a phenomenon associated with Ca²⁺ homeostasis.

Flagellin C decreases the expression of the Gossypium hirsutum cation/proton exchanger 3 gene to promote calcium ion, hydrogen peroxide, and nitric oxide and synergistically regulate the resistance of cotton to Verticillium wilt

To date, no ideal effective method for controlling Verticillium wilt in upland cotton (Gossypium hirsutum) has been defined. The purpose of this study was to determine the effects and mechanism through which flagellin C (FLiC) regulates the Gossypium hirsutum cation/proton exchanger 3 gene (GhCAX3), induces plant immunity, and increases resistance to Verticillium wilt. The FLiC gene was cloned from an endophytic bacterium (Pseudomonas) isolated from roots of the upland cotton cultivar Zhongmiansuo 41. The biocontrol effects of FLiC purified in vitro on resistant and susceptible upland cotton cultivars were 47.50 and 32.42%, respectively. FLiC induced a hypersensitive response (HR) in leaves of tobacco and immune responses in upland cotton. Transcriptome data showed that treatment with FLiC significantly enriched the calcium antiporter activity-associated disease-resistant metabolic pathway in seedlings. Moreover, FLiC downregulated GhCAX3 expression to increase intracellular calcium ion (Ca²⁺) content and stimulate increases in the intracellular hydrogen peroxide (H₂O₂) and nitric oxide (NO) contents. The coordinated regulation of Ca²⁺, H₂O₂, and NO enhanced cotton resistance to Verticillium wilt. Furthermore, transgenic Arabidopsis plants overexpressing FLiC showed significantly improved resistance to Verticillium wilt. FLiC may be used as a resistance gene and a regulator to improve resistance to Verticillium dahliae (VD) in upland cotton.

Distinct Responses to Pathogenic and Symbionic Microorganisms: The Role of Plant Immunity

Plants must balance both beneficial (symbiotic) and pathogenic challenges from microorganisms, the former benefitting the plant and agriculture and the latter causing disease and economic harm. Plant innate immunity describes a highly conserved set of defense mechanisms that play pivotal roles in sensing immunogenic signals associated with both symbiotic and pathogenic microbes and subsequent downstream activation of signaling effector networks that protect the plant. An intriguing question is how the innate immune system distinguishes “friends” from “foes”. Here, we summarize recent advances in our understanding of the role and spectrum of innate immunity in recognizing and responding to different microbes. In addition, we also review some of the strategies used by microbes to manipulate plant signaling pathways and thus evade immunity, with emphasis on the use of effector proteins and micro-RNAs (miRNAs). Furthermore, we discuss potential questions that need addressing to advance the field of plant–microbe interactions.

Calcium channels and transporters: Roles in response to biotic and abiotic stresses

Calcium (Ca²⁺) serves as a ubiquitous second messenger by mediating various signaling pathways and responding to numerous environmental conditions in eukaryotes. Therefore, plant cells have developed complex mechanisms of Ca²⁺ communication across the membrane, receiving the message from their surroundings and transducing the information into cells and organelles. A wide range of biotic and abiotic stresses cause the increase in [Ca²⁺]_cyt as a result of the Ca²⁺ influx permitted by membrane-localized Ca²⁺ permeable cation channels such as CYCLIC NUCLEOTIDE-GATE CHANNELs (CNGCs), and voltage-dependent HYPERPOLARIZATION-ACTIVATED CALCIUM²⁺ PERMEABLE CHANNELs (HACCs), as well as GLUTAMATE RECEPTOR-LIKE RECEPTORs (GLRs) and TWO-PORE CHANNELs (TPCs). Recently, resistosomes formed by some NUCLEOTIDE-BINDING LEUCINE-RICH REPEAT RECEPTORs (NLRs) are also proposed as a new type of Ca²⁺ permeable cation channels. On the contrary, some Ca²⁺ transporting membrane proteins, mainly Ca²⁺-ATPase and Ca²⁺/H⁺ exchangers, are involved in Ca²⁺ efflux for removal of the excessive [Ca²⁺]_cyt in order to maintain the Ca²⁺ homeostasis in cells. The Ca²⁺ efflux mechanisms mediate the wide ranges of cellular activities responding to external and internal stimuli. In this review, we will summarize and discuss the recent discoveries of various membrane proteins involved in Ca²⁺ influx and efflux which play an essential role in fine-tuning the processing of information for plant responses to abiotic and biotic stresses.

Role of PsnWRKY70 in Regulatory Network Response to Infection with Alternaria alternata (Fr.) Keissl in Populus

WRKY is an important complex family of transcription factors involved in plant immune responses. Among them, WRKY70 plays an important role in the process of the plant defense response to the invasion of pathogens. However, the defense mechanism of PsnWRKY70 is not clear in Populus nigra. In this study, we showed that PsnWRKY70-overexpression lines (OE) had fewer leaf blight symptoms than PsnWRKY70-repressing lines (RE). PsnWRKY70 activated MAP kinase cascade genes (PsnM2K4, PsnMPK3, PsnM3K18), calcium channel proteins-related genes (PsnCNG3, PsnCNGC1, PsnCNG4), and calcium-dependent protein kinases genes (PsnCDPKL, PsnCDPKW, PsnCDPKS, PsnCDPKQ). Furthermore, 129 genes of PsnWRKY70 putative genome-wide direct targets (DTGs) were identified by using transcriptome (RNA-seq) and DNA affinity purification sequencing (DAP-seq). PsnWRKY70 directly binds to the promoters of homologous genes and LRR domain proteins to promote the expression of WRKY6, WRKY18, WRKY22, and WRKY22–1, LRR domain proteins LRR8, LRR-RLK, ADR1-like 2, NB-ARC, etc. Our study suggests that PsnWRKY70 enhances the resistance of A. alternata in poplar by activating genes in both pathogen-associated molecular pattern-triggered immunity (PTI) and effector-triggered immunity (ETI).

Rapid responses: Receptor-like kinases directly regulate the functions of membrane transport proteins in plants

Receptor-like kinases (RLKs) are a large group of plant-specific transmembrane proteins mainly acting as receptors or co-receptors of various extracellular signals. They usually turn extracellular signals into intracellular responses via altering gene expression profiles. However, recent studies confirmed that many RLKs can physically interact with diverse membrane-localized transport proteins and regulate their activities for speedy responses in limited tissues or cells. In this minireview, we highlight recent discoveries regarding how RLKs can work with membrane transport proteins collaboratively and thereby trigger cellular responses in a precise and rapid manner. It is anticipated that such regulation broadly presents in plants and more examples will be gradually revealed when in-depth analyses are conducted for the functions of RLKs.

Regulation of plant responses to biotic and abiotic stress by receptor-like cytoplasmic kinases

As sessile organisms, plants have to cope with environmental change and numerous biotic and abiotic stress. Upon perceiving environmental cues and stress signals using different types of receptors, plant cells initiate immediate and complicated signaling to regulate cellular processes and respond to stress. Receptor-like cytoplasmic kinases (RLCKs) transduce signals from receptors to cellular components and play roles in diverse biological processes. Recent studies have revealed the hubbing roles of RLCKs in plant responses to biotic stress. Emerging evidence indicates the important regulatory roles of RLCKs in plant responses to abiotic stress, growth, and development. As a pivot of cellular signaling, the activity and stability of RLCKs are dynamically and tightly controlled. Here, we summarize the current understanding of how RLCKs regulate plant responses to biotic and abiotic stress.