Calcium/calmodulin-mediated regulation of plant immunity

MicroRNA1432 regulates rice drought stress tolerance by targeting the CALMODULIN-LIKE2 gene

Due to climate change, drought has become a major threat to rice (Oryza sativa L.) growth and yield worldwide. Understanding the genetic basis of drought tolerance in rice is therefore of great importance. Here, we identified a microRNA, miR1432, which regulates rice drought tolerance by targeting the CALMODULIN-LIKE2 (OsCaML2) gene. Mutation of MIR1432 or suppression of miR1432 expression significantly impaired seed germination and seedling growth under drought-stress conditions. Molecular analysis demonstrated that miR1432 affected rice drought tolerance by directly targeting OsCaML2, which encodes an EF-hand chiral calcium-binding protein. Overexpression of a miR1432-resistant form of OsCaML2 (OEmCaML2) phenocopied the mir1432 mutant and miR1432 suppression plants. Furthermore, the suppression of miR1432 severely affected the expression of genes involved in responses to stimulation, metabolism and signal transduction, especially the mitogen-activated protein kinase (MAPK) pathway and hormone transduction pathway in rice under drought stress. Thus, our findings show that the miR1432-OsCaML2 module plays an important role in the regulation of rice drought tolerance, suggesting its potential utilization in developing molecular breeding strategies that improve crop drought tolerance.

Positive roles of the Ca2+ sensors GbCML45 and GbCML50 in improving cotton Verticillium wilt resistance

As a universal second messenger, cytosolic calcium (Ca2+) functions in multifaceted intracellular processes, including growth, development and responses to biotic/abiotic stresses in plant. The plant-specific Ca2+ sensors, calmodulin and calmodulin-like (CML) proteins, function as members of the second-messenger system to transfer Ca2+ signal into downstream responses. However, the functions of CMLs in the responses of cotton (Gossypium spp.) after Verticillium dahliae infection, which causes the serious vascular disease Verticillium wilt, remain elusive. Here, we discovered that the expression level of GbCML45 was promoted after V. dahliae infection in roots of cotton, suggesting its potential role in Verticillium wilt resistance. We found that knockdown of GbCML45 in cotton plants decreased resistance while overexpression of GbCML45 in Arabidopsis thaliana plants enhanced resistance to V. dahliae infection. Furthermore, there was physiological interaction between GbCML45 and its close homologue GbCML50 by using yeast two-hybrid and bimolecular fluorescence assays, and both proteins enhanced cotton resistance to V. dahliae infection in a Ca2+-dependent way in a knockdown study. Detailed investigations indicated that several defence-related pathways, including salicylic acid, ethylene, reactive oxygen species and nitric oxide signalling pathways, as well as accumulations of lignin and callose, are responsible for GbCML45- and GbCML50-modulated V. dahliae resistance in cotton. These results collectively indicated that GbCML45 and GbCML50 act as positive regulators to improve cotton Verticillium wilt resistance, providing potential targets for exploitation of improved Verticillium wilt-tolerant cotton cultivars by genetic engineering and molecular breeding.

WGCNA Reveals Hub Genes and Key Gene Regulatory Pathways of the Response of Soybean to Infection by Soybean mosaic virus

Soybean mosaic virus (SMV) is one of the main pathogens that can negatively affect soybean production and quality. To study the gene regulatory network of soybeans in response to SMV SC15, the resistant line X149 and susceptible line X97 were subjected to transcriptome analysis at 0, 2, 8, 12, 24, and 48 h post-inoculation (hpi). Differential expression analysis revealed that 10,190 differentially expressed genes (DEGs) responded to SC15 infection. Weighted gene co-expression network analysis (WGCNA) was performed to identify highly related resistance gene modules; in total, eight modules, including 2256 DEGs, were identified. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis of 2256 DEGs revealed that the genes significantly clustered into resistance-related pathways, such as the plant-pathogen interaction pathway, mitogen-activated protein kinases (MAPK) signaling pathway, and plant hormone signal transduction pathway. Among these pathways, we found that the flg22, Ca2+, hydrogen peroxide (H2O2), and abscisic acid (ABA) regulatory pathways were fully covered by 36 DEGs. Among the 36 DEGs, the gene Glyma.01G225100 (protein phosphatase 2C, PP2C) in the ABA regulatory pathway, the gene Glyma.16G031900 (WRKY transcription factor 22, WRKY22) in Ca2+ and H2O2 regulatory pathways, and the gene Glyma.04G175300 (calcium-dependent protein kinase, CDPK) in Ca2+ regulatory pathways were highly connected hub genes. These results indicate that the resistance of X149 to SC15 may depend on the positive regulation of flg22, Ca2+, H2O2, and ABA regulatory pathways. Our study further showed that superoxide dismutase (SOD) activity, H2O2 content, and catalase (CAT) and peroxidase (POD) activities were significantly up-regulated in the resistant line X149 compared with those in 0 hpi. This finding indicates that the H2O2 regulatory pathway might be dependent on flg22- and Ca2+-pathway-induced ROS generation. In addition, two hub genes, Glyma.07G190100 (encoding F-box protein) and Glyma.12G185400 (encoding calmodulin-like proteins, CMLs), were also identified and they could positively regulate X149 resistance. This study provides pathways for further investigation of SMV resistance mechanisms in soybean.

Interactive transcriptome analyses of Northern Wild Rice (Zizania palustris L.) and Bipolaris oryzae show convoluted communications during the early stages of fungal brown spot development

Fungal diseases, caused mainly by Bipolaris spp., are past and current threats to Northern Wild Rice (NWR) grain production and germplasm preservation in both natural and cultivated settings. Genetic resistance against the pathogen is scarce. Toward expanding our understanding of the global gene communications of NWR and Bipolaris oryzae interaction, we designed an RNA sequencing study encompassing the first 12 h and 48 h of their encounter. NWR activated numerous plant recognition receptors after pathogen infection, followed by active transcriptional reprogramming of signaling mechanisms driven by Ca2+ and its sensors, mitogen-activated protein kinase cascades, activation of an oxidative burst, and phytohormone signaling-bound mechanisms. Several transcription factors associated with plant defense were found to be expressed. Importantly, evidence of diterpenoid phytoalexins, especially phytocassane biosynthesis, among expression of other defense genes was found. In B. oryzae, predicted genes associated with pathogenicity including secreted effectors that could target plant defense mechanisms were expressed. This study uncovered the early molecular communication between the NWR-B. oryzae pathosystem, which could guide selection for allele-specific genes to boost NWR defenses, and overall aid in the development of more efficient selection methods in NWR breeding through the use of the most virulent fungal isolates.

The chromosome-scale genome and the genetic resistance machinery against insect herbivores of the Mexican toloache, Datura stramonium

Plant resistance refers to the heritable ability of plants to reduce damage caused by natural enemies, such as herbivores and pathogens, either through constitutive or induced traits like chemical compounds or trichomes. However, the genetic architecture-the number and genome location of genes that affect plant defense and the magnitude of their effects-of plant resistance to arthropod herbivores in natural populations remains poorly understood. In this study, we aimed to unveil the genetic architecture of plant resistance to insect herbivores in the annual herb Datura stramonium (Solanaceae) through quantitative trait loci mapping. We achieved this by assembling the species' genome and constructing a linkage map using an F2 progeny transplanted into natural habitats. Furthermore, we conducted differential gene expression analysis between undamaged and damaged plants caused by the primary folivore, Lema daturaphila larvae. Our genome assembly resulted in 6,109 scaffolds distributed across 12 haploid chromosomes. A single quantitative trait loci region on chromosome 3 was associated with plant resistance, spanning 0 to 5.17 cM. The explained variance by the quantitative trait loci was 8.44%. Our findings imply that the resistance mechanisms of D. stramonium are shaped by the complex interplay of multiple genes with minor effects. Protein-protein interaction networks involving genes within the quantitative trait loci region and overexpressed genes uncovered the key role of receptor-like cytoplasmic kinases in signaling and regulating tropane alkaloids and terpenoids, which serve as powerful chemical defenses against D. stramonium herbivores. The data generated in our study constitute important resources for delving into the evolution and ecology of secondary compounds mediating plant-insect interactions.

Ca2+/calmodulin-mediated desensitization of glutamate receptors shapes plant systemic wound signalling and anti-herbivore defence

Plants rely on systemic signalling mechanisms to establish whole-body defence in response to insect and nematode attacks. GLUTAMATE RECEPTOR-LIKE (GLR) genes have been implicated in long-distance transmission of wound signals to initiate the accumulation of the defence hormone jasmonate (JA) at undamaged distal sites. The systemic signalling entails the activation of Ca2+-permeable GLR channels by wound-released glutamate, triggering membrane depolarization and cytosolic Ca2+ influx throughout the whole plant. The systemic electrical and calcium signals rapidly dissipate to restore the resting state, partially due to desensitization of the GLR channels. Here we report the discovery of calmodulin-mediated, Ca2+-dependent desensitization of GLR channels, revealing a negative feedback loop in the orchestration of plant systemic wound responses. A CRISPR-engineered GLR3.3 allele with impaired desensitization showed prolonged systemic electrical signalling and Ca2+ waves, leading to enhanced plant defence against herbivores. Moreover, this Ca2+/calmodulin-mediated desensitization of GLR channels is a highly conserved mechanism in plants, providing a potential target for engineering anti-herbivore defence in crops.

The Interactions between Two Fungal Endophytes Epicoccum layuense R2-21 and Alternaria alternata XHYN2 and Grapevines (Vitis vinifera) with De Novo Established Symbionts under Aseptic Conditions

In this study, we focused on grapevine-endophyte interactions and reprogrammed secondary metabolism in the host plant due to defense against the colonization of endophytes. Thus, the transcriptional responses of tissue cultured grapevine seedlings (Vitis vinifera L. cv.: Cabernet Sauvignon) to two fungal endophytes Epicoccum layuense R2-21 (Epi R2-21) and Alternaria alternata XHYN2 (Alt XHYN2) at three different time points (6 h, 6 d, 15 d) were analyzed. As expected, a total of 5748 and 5817 differentially expressed genes (DEGs) were separately initiated in Epi R2-21 and Alt XHYN2 symbiotic tissue cultured seedlings compared to no endophyte treatment. The up-regulated DEGs at all time points in Epi R2-21- or Alt XHYN2-treated seedlings were mainly enriched in the flavonoid biosynthesis, phenylpropanoid biosynthesis, phenylalanine metabolism, stilbenoid, diarylheptanoid and gingerol biosynthesis, and circadian rhythm-plant pathways. In addition, the up-regulated DEGs at all sampling times in Alt XHYN2-treated tissue cultured seedlings were enriched in the plant-pathogen interaction pathway, but appeared in Epi R2-21 symbiotic seedlings only after 15 d of treatment. The down-regulated DEGs were not enriched in any KEGG pathways after 6 h inoculation for Epi R2-21 and Alt XHYN2 treatments, but were enriched mainly in photosynthesis-antenna proteins and plant hormone signal transduction pathways at other sampling times. At three different time points, a total of 51 DEGs (all up-regulated, 1.33-10.41-fold) were involved in secondary metabolism, and 22 DEGs (all up-regulated, 1.01-8.40-fold) were involved in defense responses in endophytic fungi symbiotic tissue cultured seedlings. The protein-protein interaction (PPI) network demonstrated that genes encoding CHS (VIT_10s0042g00920, VIT_14s0068g00920, and VIT_16s0100g00910) and the VIT_11s0065g00350 gene encoding CYP73A mediated the defense responses, and might induce more defense-associated metabolites. These results illustrated the activation of stress-associated secondary metabolism in the host grapevine during the establishment of fungi-plant endophytism. This work provides avenues for reshaping the qualities and characteristics of wine grapes utilizing specific endophytes and better understanding plant-microbe interactions.

Genome-wide investigation and expression analysis of OSCA gene family in response to abiotic stress in alfalfa

Alfalfa is an excellent leguminous forage crop that is widely cultivated worldwide, but its yield and quality are often affected by drought and soil salinization. Hyperosmolality-gated calcium-permeable channel (OSCA) proteins are hyperosmotic calcium ion (Ca2+) receptors that play an essential role in regulating plant growth, development, and abiotic stress responses. However, no systematic analysis of the OSCA gene family has been conducted in alfalfa. In this study, a total of 14 OSCA genes were identified from the alfalfa genome and classified into three groups based on their sequence composition and phylogenetic relationships. Gene structure, conserved motifs and functional domain prediction showed that all MsOSCA genes had the same functional domain DUF221. Cis-acting element analysis showed that MsOSCA genes had many cis-regulatory elements in response to abiotic or biotic stresses and hormones. Tissue expression pattern analysis demonstrated that the MsOSCA genes had tissue-specific expression; for example, MsOSCA12 was only expressed in roots and leaves but not in stem and petiole tissues. Furthermore, RT-qPCR results indicated that the expression of MsOSCA genes was induced by abiotic stress (drought and salt) and hormones (JA, SA, and ABA). In particular, the expression levels of MsOSCA3, MsOSCA5, MsOSCA12 and MsOSCA13 were significantly increased under drought and salt stress, and MsOSCA7, MsOSCA10, MsOSCA12 and MsOSCA13 genes exhibited significant upregulation under plant hormone treatments, indicating that these genes play a positive role in drought, salt and hormone responses. Subcellular localization results showed that the MsOSCA3 protein was localized on the plasma membrane. This study provides a basis for understanding the biological information and further functional analysis of the MsOSCA gene family and provides candidate genes for stress resistance breeding in alfalfa.

Involvement of the Calmodulin-like Protein Gene VaCML92 in Grapevine Abiotic Stress Response and Stilbene Production

Calmodulin-like proteins (CMLs) are an important family of plant calcium sensor proteins that sense and decode changes in the intracellular calcium concentration in response to environmental and developmental stimuli. Nonetheless, the specific functions of individual CML family members remain largely unknown. This study aims to explore the role of the Vitis amurensis VaCML92 gene in the development of its high stress resistance and the production of stilbenes. The expression of VaCML92 was sharply induced in V. amurensis cuttings after cold stress. The VaCML92 gene was cloned and its role in the abiotic stress responses and stilbene production in grapevine was further investigated. The VaCML92-overexpressing callus cell cultures of V. amurensis and soil-grown plants of Arabidopsis thaliana exhibited enhanced tolerance to cold stress and, to a lesser extent, to the drought, while their tolerance to heat stress and high salinity was not affected. In addition, the overexpression of VaCML92 increased stilbene production in the V. amurensis cell cultures by 7.8-8.7-fold. Taken together, the data indicate that the VaCML92 gene is involved as a strong positive regulator in the rapid response to cold stress, the induction of cold stress resistance and in stilbene production in wild grapevine.

Comparative transcriptome analysis reveals key pathways and regulatory networks in early resistance of Glycine max to soybean mosaic virus

As a high-value oilseed crop, soybean [Glycine max (L.) Merr.] is limited by various biotic stresses during its growth and development. Soybean mosaic virus (SMV) is a devastating viral infection of soybean that primarily affects young leaves and causes significant production and economic losses; however, the synergistic molecular mechanisms underlying the soybean response to SMV are largely unknown. Therefore, we performed RNA sequencing on SMV-infected resistant and susceptible soybean lines to determine the molecular mechanism of resistance to SMV. When the clean reads were aligned to the G. max reference genome, a total of 36,260 genes were identified as expressed genes and used for further research. Most of the differentially expressed genes (DEGs) associated with resistance were found to be enriched in plant hormone signal transduction and circadian rhythm according to Kyoto Encyclopedia of Genes and Genomes analysis. In addition to salicylic acid and jasmonic acid, which are well known in plant disease resistance, abscisic acid, indole-3-acetic acid, and cytokinin are also involved in the immune response to SMV in soybean. Most of the Ca2+ signaling related DEGs enriched in plant-pathogen interaction negatively influence SMV resistance. Furthermore, the MAPK cascade was involved in either resistant or susceptible responses to SMV, depending on different downstream proteins. The phytochrome interacting factor-cryptochrome-R protein module and the MEKK3/MKK9/MPK7-WRKY33-CML/CDPK module were found to play essential roles in soybean response to SMV based on protein-protein interaction prediction. Our findings provide general insights into the molecular regulatory networks associated with soybean response to SMV and have the potential to improve legume resistance to viral infection.

A unique resistance mechanism is associated with RBgh2 barley powdery mildew adult plant resistance

KEY MESSAGE

Gene expression at the RBgh2 locus indicates involvement in cAMP/G-protein-coupled signalling and innate immunity in barley powdery mildew adult plant resistance. Barley powdery mildew is a globally significant disease, responsible for reduced grain yield and quality. A major effect adult plant resistance gene, RBgh2, was previously found in a landrace from Azerbaijan. The atypical phenotype suggested different underlying genetic factors compared to conventional resistance genes and to investigate this, genome-wide gene expression was compared between sets of heterogeneous doubled haploids. RBgh2 resistance is recessive and induces both temporary genome-wide gene expression changes during powdery mildew infection together with constitutive changes, principally at the RBgh2 locus. Defence-related genes significantly induced included homologues of genes associated with innate immunity and pathogen recognition. Intriguingly, RBgh2 resistance does not appear to be dependent on salicylic acid signalling, a key pathway in plant resistance to biotrophs. Constitutive co-expression of resistance gene homologues was evident at the 7HS RBgh2 locus, while no expression was evident for a 6-transmembrane gene, predicted in silico to contain both G-protein- and calmodulin-binding domains. The gene was disrupted at the 5' end, and G-protein-binding activity was suppressed. RBgh2 appears to operate through a unique mechanism that co-opts elements of innate immunity.

Nanomaterial Size and Surface Modification Mediate Disease Resistance Activation in Cucumber (Cucumis sativus)

Crop disease represents a serious and increasing threat to global food security. Lanthanum oxide nanomaterials (La₂O₃ NMs) with different sizes (10 and 20 nm) and surface modifications (citrate, polyvinylpyrrolidone [PVP], and poly(ethylene glycol)) were investigated for their control of the fungal pathogen Fusarium oxysporum (Schl.) f. sp cucumerinum Owen on six-week-old cucumber (Cucumis sativus) in soil. Seed treatment and foliar application of the La₂O₃ NMs at 20-200 mg/kg (mg/L) significantly suppressed cucumber wilt (decreased by 12.50-52.11%), although the disease control efficacy was concentration-, size-, and surface modification-dependent. The best pathogen control was achieved by foliar application of 200 mg/L PVP-coated La₂O₃ NMs (10 nm); disease severity was decreased by 67.6%, and fresh shoot biomass was increased by 49.9% as compared with pathogen-infected control. Importantly, disease control efficacy was 1.97- and 3.61-fold greater than that of La₂O₃ bulk particles and a commercial fungicide (Hymexazol), respectively. Additionally, La₂O₃ NMs application enhanced cucumber yield by 350-461%, increased fruit total amino acids by 295-344%, and improved fruit vitamin content by 65-169% as compared with infected controls. Transcriptomic and metabolomic analyses revealed that La₂O₃ NMs: (1) interacted with calmodulin, subsequently activating salicylic acid-dependent systemic acquired resistance; (2) increased the activity and expression of antioxidant and related genes, thereby alleviating pathogen-induced oxidative stress; and (3) directly inhibited in vivo pathogen growth. The findings highlight the significant potential of La₂O₃ NMs for suppressing plant disease in sustainable agriculture.

Pathogen-induced autophagy regulates monolignol transport and lignin formation in plant immunity

The evolutionary plant-pathogen arms race has equipped plants with the immune system that can defend against pathogens. Pattern-triggered immunity and effector-triggered immunity are two major branches of innate immunity that share immune responses, including oxidative bursts, transcriptional reprogramming, and cell wall modifications such as lignin deposition. In a previous study, we reported that lignin rapidly accumulates in pathogen-infected Arabidopsis leaves and acts as a mechanical barrier, spatially restricting pathogens and cell death. Lignin deposition into the cell wall is a three-step process: monolignol biosynthesis, transport, and polymerization. While monolignol biosynthesis and polymerization are relatively well understood, the mechanism of monolignol transport remains unclear. In this study, we show that macroautophagy/autophagy modulates pathogen-induced lignin formation. Lignification and other immune responses were impaired in autophagy-defective atg (autophagy-related) mutants. In microscopy analyses, monolignols formed punctate structures in response to pathogen infection and colocalized with autophagic vesicles. Furthermore, autophagic activity and lignin accumulation were both enhanced in dnd1 (defense, no death 1) mutant with elevated disease resistance but no cell death and crossing dnd1-1 with atg mutants resulted in a lignin deficit, further supporting that lignin formation requires autophagy. Collectively, these findings demonstrate that lignification, particularly monolignol transport, is achieved through autophagic membrane trafficking in plant immunity.Abbreviations: ABC transporter: ATP-binding cassette transporter; ACD2/AT4G37000: accelerated cell death 2; ATG: autophagy-related; C3'H/AT2G40890: p-coumaroyl shikimate 3-hydroxylase; C4H/AT2G30490: cinnamate 4-hydroxylase; CA: coniferyl alcohol; CaMV: cauliflower mosaic virus; CASP: Casparian strip membrane domain protein; CASPL: CASP-like protein; CBB: Coomassie Brilliant Blue; CCoAOMT1/AT4G34050: caffeoyl-CoA O-methyltransferase 1; CCR1/AT1G15950: cinnamoyl-CoA reductase 1; CFU: colony-forming unit; COMT1/AT5G54160: caffeic acid O-methyltransferase 1; Con A: concanamycin A; DMAC: dimethylaminocoumarin; DND1/AT5G15410: defense, no death 1; CNGC2: cyclic nucleotide-gated channel 2; ER: endoplasmic reticulum; ESB1/AT2G28670/DIR10: enhanced suberin 1; ETI: effector-triggered immunity; EV: extracellular vesicle; F5H/AT4G36220: ferulate-5-hydroxylase; Fluo-3 AM: Fluo-3 acetoxymethyl ester; GFP: green fluorescent protein; HCT/AT5G48930: p-hydroxycinnamoyl-CoA:quinate/shikimate p-hydroxycinnamoyltransferase; HR: hypersensitive response; LAC: laccase; LTG: LysoTracker Green; LSD1/AT4G200380: lesion stimulating disease 1; PAL1/AT2G37040: phenylalanine ammonia-lyase 1; PAMP: pathogen-associated molecular patterns; PCD: programmed cell death; PE: phosphatidylethanolamine; PRX: peroxidase; Pst DC3000: Pseudomonas syringe pv. tomato DC3000; PTI: pattern-triggered immunity; SA: salicylic acid; SD: standard deviation; SID2/AT1G7410: SA induction-deficient 2; UGT: UDP-glucosyltransferase; UPLC: ultraperformance liquid chromatography; UPS: unconventional protein secretion; V-ATPase: vacuolar-type H⁺-translocating ATPase.

Genome-wide analysis of the CML gene family and its response to melatonin in common bean (Phaseolus vulgaris L.)

Calmodulin-like proteins (CML) are important calcium signal transduction proteins in plants. CML genes have been analyzed in several plants. However, little information on CML in Phaseolus vulgare is available. In this study, we identified 111 PvCMLs distributed on eleven chromosomes. Phylogenetic analysis classified them into seven subfamilies. Cis-acting element prediction showed that PvCML contained elements related to growth and development, response to abiotic stress and hormones. Moreover, the majority of PvCMLs showed different expression patterns in most of the nine tissues and developmental stages which indicated the role of PvCML in the growth and development of common bean. Additionally, the common bean was treated with melatonin by seed soaking, and root transcriptome at the 5th day and qRT-PCR of different tissue at several stages were performed to reveal the response of PvCML to the hormone. Interestingly, 9 PvCML genes of subfamily VI were detected responsive to exogenous melatonin, and the expression dynamics of nine melatonin response PvCML genes after seed soaking with melatonin were revealed. Finally, the protein interaction network analysis of nine melatonin responsive PvCMLs was constructed. The systematic analysis of the PvCML gene family provides theoretical support for the further elucidation of their functions, and melatonin response molecular mechanism of the CML family in P. vulgaris.

Enhanced Resistance to Sclerotinia sclerotiorum in Brassica rapa by Activating Host Immunity through Exogenous Verticillium dahliae Aspf2-like Protein (VDAL) Treatment

Sclerotinia stem rot caused by Sclerotinia sclerotiorum is one of the most destructive diseases in Brassica rapa. Verticillium dahliae Aspf2-like protein (VDAL) is a secretory protein of V. dahliae which has been shown to enhance the resistance against fungal infections in several plants. Nonetheless, the molecular mechanisms of VDAL-primed disease resistance are still poorly understood. In this study, we performed physiological, biochemical, and transcriptomic analyses of Brassica rapa in order to understand how VDAL confers resistance to S. sclerotiorumn infections in plants. The results showed that foliar application of VDAL significantly reduced the plaque area on leaves inoculated with S. sclerotiorum. It also enhanced antioxidant capacity by increasing activities of superoxide dismutase (SOD), peroxidase (POD), peroxidase (APX), glutathione reductase (GR), protoporphyrinogen oxidase (PPO), and defense-related enzymes β-1,3-glucanase and chitinase during the infection periods. This occurred in parallel with significantly reduced relative conductivity at different periods and lower malondialdehyde (MDA) content as compared to sole S. sclerotiorum inoculation. Transcriptomic analysis showed a total of 146 (81 up-regulated and 65 down-regulated) differentially expressed genes (DEGs) in VDAL-treated leaves compared to the control. The most enriched three Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were the mitogen-activated protein kinase (MAPK) signaling pathway, plant hormone signal transduction, and plant-pathogen interaction, all of which were associated with plant immunity. DEGs associated with MAPK and hormone signal transduction pathways were ethylene response sensor ERS2, EIN3 (Ethylene Insensitive3)-binding F-box protein 2 (EBF2), ethylene-responsive transcription factor ERF94, MAPK 9 (MKK9), protein phosphatase 2C (PP2C37), auxin-responsive proteins (AUX/IAA1 and 19), serine/threonine-protein kinase CTR1, and abscisic acid receptors (PLY 4 and 5). Among the DEGs linked with the plant-pathogen interaction pathway were calmodulin-like proteins (CML5, 24, 27), PTI1-like tyrosine protein kinase 3 (Pti13) and transcription factor MYB30, all of which are known to play key roles in pathogen-associated molecular pattern (PAMP)-triggered immunity and effector-triggered immunity (ETI) for hypersensitive response (HR), cell wall reinforcement, and stomatal closure in plants. Overall, VDLA treatment triggered repression of the auxin and ABA signaling pathways and de-repression of the ethylene signaling pathways in young B. rapa seedlings to increase plant innate immunity. Our results showed that VDAL holds great potential to enhance fungal disease resistance in B. rapa crop.

Genome-wide association study for resistance to Pseudomonas syringae pv. garcae in Coffea arabica

Bacteria halo blight (BHB), a coffee plant disease caused by Pseudomonas syringae pv. garcae, has been gaining importance in producing mountain regions and mild temperatures areas as well as in coffee nurseries. Most Coffea arabica cultivars are susceptible to this disease. In contrast, a great source of genetic diversity and resistance to BHB are found in C. arabica Ethiopian accessions. Aiming to identify quantitative trait nucleotides (QTNs) associated with resistance to BHB and the influence of these genomic regions during the domestication of C. arabica, we conducted an analysis of population structure and a Genome-Wide Association Study (GWAS). For this, we used genotyping by sequencing (GBS) and phenotyping for resistance to BHB of a panel with 120 C. arabica Ethiopian accessions from a historical FAO collection, 11 C. arabica cultivars, and the BA-10 genotype. Population structure analysis based on single-nucleotide polymorphisms (SNPs) markers showed that the 132 accessions are divided into 3 clusters: most wild Ethiopian accessions, domesticated Ethiopian accessions, and cultivars. GWAS, using the single-locus model MLM and the multi-locus models mrMLM, FASTmrMLM, FASTmrEMMA, and ISIS EM-BLASSO, identified 11 QTNs associated with resistance to BHB. Among these QTNs, the four with the highest values of association for resistance to BHB are linked to g000 (Chr_0_434_435) and g010741 genes, which are predicted to encode a serine/threonine-kinase protein and a nucleotide binding site leucine-rich repeat (NBS-LRR), respectively. These genes displayed a similar transcriptional downregulation profile in a C. arabica susceptible cultivar and in a C. arabica cultivar with quantitative resistance, when infected with P. syringae pv. garcae. However, peaks of upregulation were observed in a C. arabica cultivar with qualitative resistance, for both genes. Our results provide SNPs that have potential for application in Marker Assisted Selection (MAS) and expand our understanding about the complex genetic control of the resistance to BHB in C. arabica. In addition, the findings contribute to increasing understanding of the C. arabica domestication history.

The Apple Receptor-Like Kinase MdSRLK3 Positively Regulates Resistance Against Pathogenic Fungus Valsa mali by Affecting the Ca2+ Signaling Pathway

Valsa mali is the main pathogenic fungus that causes the apple Valsa canker, a destructive disease severely threatening apple production in the world. However, the underlying key components involved in resistance against V. mali in apple trees remain largely unexplored. Here, we isolated and functionally characterized a G-type lectin S-receptor-like protein kinase MdSRLK3 from the cultivar Royal Gala derivative line GL-3. qRT-PCR showed that the relative expression of MdSRLK3 in apple branches reached its highest level at 24 h post V. mali inoculation, which was 13.42 times higher than without inoculation. Transient overexpression of MdSRLK3 enhanced apple resistance against V. mali, while transient silencing of MdSRLK3 reduced its resistance against the pathogen. More importantly, stable silencing of MdSRLK3 resulted in reduced resistance against this fungus. Furthermore, we demonstrated that MdSRLK3 positively regulated apple resistance by affecting the Ca²⁺ signaling pathway, and the regulation was also related to the H₂O₂ and callose signaling pathways. Overall, our data reveal that MdSRLK3 is a positive regulator of apple immunity.

TMT-based quantitative membrane proteomics identified PRRs potentially involved in the perception of MSP1 in rice leaves

Pathogen-associated molecular patterns (PAMPs) play a key role in triggering PAMPs triggered immunity (PTI) in plants. In the case of the rice-Magnaporthe oryzae pathosystem, fewer PAMPs and their pattern recognition receptors (PRRs) have been characterized. Recently, a M. oryzae snodprot1 homolog protein (MSP1) has been identified that functions as PAMP and triggering the PTI responses in rice. However, the molecular mechanism underlying MSP1-induced PTI is currently elusive. Therefore, we generated MSP1 overexpressed transgenic lines of rice, and a tandem mass tag (TMT)-based quantitative membrane proteomic analysis was employed to decipher the potential MSP1-induced signaling in rice using total cytosolic as well as membrane protein fractions. This approach led to the identification of 8033 proteins of which 1826 were differentially modulated in response to overexpression of MSP1 and/or exogenous jasmonic acid treatment. Of these, 20 plasma membrane-localized receptor-like kinases (RLKs) showed increased abundance in MSP1 overexpression lines. Moreover, activation of proteins related to the protein degradation and modification, calcium signaling, redox, and MAPK signaling was observed in transgenic lines expressing MSP1 in the apoplast. Taken together, our results identified potential PRR candidates involved in MSP1 recognition and suggested the overview mechanism of the MSP1-induced PTI signaling in rice leaves. SIGNIFICANCE: In plants, recognition of pathogen pathogen-derived molecules, such as PAMPs, by plant plant-derived PRRs has an essential role for in the activation of PTI against pathogen invasion. Typically, PAMPs are recognized by plasma membrane (PM) localized PRRs, however, identifying the PM-localized PRR proteins is challenging due to their low abundance. In this study, we performed an integrated membrane protein enrichment by microsomal membrane extraction (MME) method and subsequent TMT-labeling-based quantitative proteomic analysis using MSP1 overexpressed rice. Based on these results, we successfully identified various intracellular and membrane membrane-localized proteins that participated in the MSP1-induced immune response and characterized the potential PM-localized PRR candidates in rice.

BcMettl4-Mediated DNA Adenine N6-Methylation Is Critical for Virulence of Botrytis cinerea

DNA adenine N⁶-methylation (6mA) plays a critical role in various biological functions, but its occurrence and functions in filamentous plant pathogens are largely unexplored. Botrytis cinerea is an important pathogenic fungus worldwide. A systematic analysis of 6mA in B. cinerea was performed in this study, revealing that 6mA is widely distributed in the genome of this fungus. The 2 kb regions flanking many genes, particularly the upstream promoter regions, were susceptible to methylation. The role of BcMettl4, a 6mA methyltransferase, in the virulence of B. cinerea was investigated. BcMETTL4 disruption and point mutations of its catalytic motif “DPPW” both resulted in significant 6mA reduction in the genomic DNA and in reduced virulence of B. cinerea. RNA-Seq analysis revealed a total of 13 downregulated genes in the disruption mutant ΔBcMettl4 in which methylation occurred at the promoter sites. These were involved in oxidoreduction, secretory pathways, autophagy and carbohydrate metabolism. Two of these genes, BcFDH and BcMFS2, were independently disrupted. Knockout of BcFDH led to reduced sclerotium formation, while disruption of BcMFS2 resulted in dramatically decreased conidium formation and pathogenicity. These observations indicated that 6mA provides potential epigenetic markers in B. cinerea and that BcMettl4 regulates virulence in this important plant pathogen.

Tomato Response to Fusarium spp. Infection under Field Conditions: Study of Potential Genes Involved

Tomato is one of the most important horticultural crops in the world and is severely affected by Fusarium diseases. To successfully manage these diseases, new insights on the expression of plant–pathogen interaction genes involved in immunity responses to Fusarium spp. infection are required. The aim of this study was to assess the level of infection of Fusarium spp. in field tomato samples and to evaluate the differential expression of target genes involved in plant–pathogen interactions in groups presenting different infection levels. Our study was able to detect Fusarium spp. in 16 from a total of 20 samples, proving the effectiveness of the primer set designed in the ITS region for its detection, and allowed the identification of two main different species complexes: Fusarium oxysporum and Fusarium incarnatum-equiseti. Results demonstrated that the level of infection positively influenced the expression of the transcription factor WRKY41 and the CBEF (calcium-binding EF hand family protein) genes, involved in plant innate resistance to pathogens. To the best of our knowledge, this is the first time that the expression of tomato defense-related gene expression is studied in response to Fusarium infection under natural field conditions. We highlight the importance of these studies for the identification of candidate genes to incorporate new sources of resistance in tomato and achieve sustainable plant disease management.

Triticale Improvement: Mining of Genes Related to Yellow Rust Resistance in Triticale Based on Transcriptome Sequencing

Yellow (stripe) rust caused by Puccinia striiformis f. sp. tritici (Pst) is a major destructive fungal disease of small grain cereals, leading to large yield losses. The breeding of resistant varieties is an effective, sustainable way to control yellow rust. Elucidation of resistance mechanisms against yellow rust and identification of candidate genes associated with rust resistance are thus crucial. In this study, seedlings of two Triticosecale Wittmack cultivars, highly resistant Gannong No. 2 and susceptible Shida No. 1, were inoculated with Pst race CYR34. Transcriptome sequencing (RNA-seq) was then used to investigate their transcriptional responses against pathogen infection before and after the appearance of symptoms-10 and 20 days after inoculation, respectively. According to the RNA-seq data, the number of upregulated and downregulated differentially expressed genes (DEGs) in the resistant cultivar was greater than in the susceptible cultivar. A total of 2,560 DEGs commonly expressed in the two cultivars on two sampling dates were subjected to pathway analysis, which revealed that most DEGs were closely associated with defense and metabolic activities. Transcription factor enrichment analysis indicated that the expressions of NAC, WRKY, and FAR1 families were also significantly changed. Further in-depth analysis of resistance genes revealed that almost all serine/threonine-protein kinases were upregulated in the resistant cultivar. Other genes related to disease resistance, such as those encoding disease-resistance- and pathogenesis-related proteins were differentially regulated in the two cultivars. Our findings can serve as a resource for gene discovery and facilitate elucidation of the complex defense mechanisms involved in triticale resistance to Pst.

Analysis of a tetraploid cotton line Mac7 transcriptome reveals mechanisms underlying resistance against the whitefly Bemisia tabaci

Whitefly inflicts both direct and indirect losses to cotton crop. Whitefly resistant cotton germplasm is a high priority and considered among the best possible solutions to mitigate this issue. In this study, we evaluated cotton leaf curl disease (CLCuD) resistant cotton line Mac7 under whitefly stress. Furthermore, we utilized the already available transcriptome data of Mac7 concerning whitefly stress to elucidate associated mechanisms and identify functionally important genes in cotton. In transcriptomic data analysis, differentially expressed genes (DEGs) were found involved in complex relay pathways, activated on whitefly exposure. The response implicates signalling through resistance genes (R-genes), MAPK, ROS, VQs or RLKs, transcription factors, which leads to the activation of defence responses including, Ca²⁺messengers, phytohormonal cross-talk, gossypol, flavonoids, PhasiRNA and susceptibility genes (S-genes). The qRT-PCR assay of 10 functionally important genes also showed their involvement in differential responses at 24 and 48 h post whitefly infestation. Briefly, our study helps in understanding the resistant nature of Mac7 under whitefly stress.

Transcriptome Analysis of the Cf-13-Mediated Hypersensitive Response of Tomato to Cladosporium fulvum Infection

Tomato leaf mold disease caused by Cladosporium fulvum (C. fulvum) is one of the most common diseases affecting greenhouse tomato production. Cf proteins can recognize corresponding AVR proteins produced by C. fulvum, and Cf genes are associated with leaf mold resistance. Given that there are many physiological races of C. fulvum and that these races rapidly mutate, resistance to common Cf genes (such as Cf-2, Cf-4, Cf-5, and Cf-9) has decreased. In the field, Ont7813 plants (carrying the Cf-13 gene) show effective resistance to C. fulvum; thus, these plants could be used as new, disease-resistant materials. To explore the mechanism of the Cf-13-mediated resistance response, transcriptome sequencing was performed on three replicates each of Ont7813 (Cf-13) and Moneymaker (MM; carrying the Cf-0 gene) at 0, 9, and 15 days after inoculation (dai) for a total of 18 samples. In total, 943 genes were differentially expressed, specifically in the Ont7813 response process as compared to the Moneymaker response process. Gene ontology (GO) classification of these 943 differentially expressed genes (DEGs) showed that GO terms, including "hydrogen peroxide metabolic process (GO_Process)", "secondary active transmembrane transporter activity (GO_Function)", and "mismatch repair complex (GO_Component)", which were the same as 11 other GO terms, were significantly enriched. An analysis of the Kyoto Encyclopedia of Genes and Genomes (KEGG) revealed that many key regulatory genes of the Cf-13-mediated resistance response processes were involved in the "plant hormone signal transduction" pathway, the "plant-pathogen interaction" pathway, and the "MAPK signaling pathway-plant" pathway. Moreover, during C. fulvum infection, jasmonic acid (JA) and salicylic acid (SA) contents significantly increased in Ont7813 at the early stage. These results lay a vital foundation for further understanding the molecular mechanism of the Cf-13 gene in response to C. fulvum infection.

Full-Length Transcriptome Sequencing-Based Analysis of Pinus sylvestris var. mongolica in Response to Sirex noctilio Venom

Simple Summary

Sirex noctilio, as a devastating international forestry quarantine pest whose venom can cause a series of physiological changes in the host plants, such as needle wilting, yellowing, decreased transpiration rate and increased respiration rate, etc. In this study, a full-length reference transcript of Pinus sylvestris var. mongolica was constructed by combining second- and third-generation transcriptome sequencing technologies. We also identified the specific expression genes and transcription factors of P. sylvestris var. mongolica under S. noctilio venom and wounding stress. S. noctilio venom mainly induced the expression of genes related to ROS, GAPDH and GPX, and mechanical damage mainly induced the photosynthesis−related genes. The results provide a better understanding of the molecular regulation of pine trees in response to S. noctilio venom.

Abstract

Sirex noctilio is a major international quarantine pest that recently emerged in northeast China to specifically invade conifers. During female oviposition, venom is injected into the host together with its symbiotic fungus to alter the normal Pinus physiology and weaken or even kill the tree. In China, the Mongolian pine (Pinus sylvestris var. mongolica), an important wind-proof and sand-fixing species, is the unique host of S. noctilio. To explore the interplay between S. noctilio venom and Mongolian pine, we performed a transcriptome comparative analysis of a 10-year-old Mongolian pine after wounding and inoculation with S. noctilio venom. The analysis was performed at 12 h, 24 h and 72 h. PacBio ISO-seq was used and integrated with RNA-seq to construct an accurate full-length transcriptomic database. We obtained 52,963 high-precision unigenes, consisting of 48,654 (91.86%) unigenes that were BLASTed to known sequences in the public database and 4309 unigenes without any annotation information, which were presumed to be new genes. The number of differentially expressed genes (DEGs) increased with the treatment time, and the DEGs were most abundant at 72 h. A total of 706 inoculation-specific DEGs (475 upregulated and 231 downregulated) and 387 wounding-specific DEGs (183 upregulated and 204 downregulated) were identified compared with the control. Under venom stress, we identified 6 DEGs associated with reactive oxygen species (ROS) and 20 resistance genes in Mongolian pine. Overall, 52 transcription factors (TFs) were found under venom stress, 45 of which belonged to the AP2/ERF TF family and were upregulated. A total of 13 genes related to the photosystem, 3 genes related photo-regulation, and 9 TFs were identified under wounding stress. In conclusion, several novel putative genes were found in Mongolian pine by PacBio ISO seq. Meanwhile, we also identified various genes that were resistant to S. noctilio venom, such as GAPDH, GPX, CAT, FL2, CERK1, and HSP83A, etc.

Identification and Gene Mapping of the Lesion Mimic Mutant lm8015-3

Lesion mimic mutants (LMMs) exhibit spots on leaves without fungal infection pressure. The spots confer variable resistance to pathogens in different LMM, making them useful research materials. It is unclear how the rice immune system responds to infection with the fungal pathogen Magnaporthe oryzae (M. oryzae). Here, we identified a rice LMM, lm8015-3, which shows reduced resistance to M. oryzae. We used Quantitative Real-Time PCR (qRT-PCR) to observe the immune system response to M. oryzae–induced lm8015-3. Lm8015-3, obtained from an ethyl methane sulfonate (EMS)–induced Zhonghui8015 (ZH8015) library, showed orange-yellow spots starting in the seedling stage and accumulated more H2O2, resulting in severe degradation of the chloroplast. With map-based cloning, the target gene was located on chromosome 12. Once inoculated with M. oryzae, the expression level of pathogen-related genes of lm8015-3 was downregulated between 48 and 72 h. In addition, more germinating spores appeared in lm8015-3. Therefore, we conclude that M. oryzae weakening the immune system of lm8015-3 from 48 to 72 h makes lm8015-3 more susceptible to M. oryzae. These results suggested that understanding how LMMs defend against M. oryzae infection will contribute to improving rice breeding.

Quantitative Trait Locus Mapping and Identification of Candidate Genes for Resistance to Fusarium Wilt Race 7 Using a Resequencing-Based High Density Genetic Bin Map in a Recombinant Inbred Line Population of Gossypium barbadense

Fusarium wilt caused by Fusarium oxysporum f. sp. vasinfectum (FOV) is one of the most destructive diseases in cotton (Gossypium spp.) production, and use of resistant cultivars is the most cost-effective method managing the disease. To understand the genetic basis of cotton resistance to FOV race 7 (FOV7), this study evaluated a recombinant inbred line (RIL) population of 110 lines of G. barbadense from a cross between susceptible Xinhai 14 and resistant 06-146 in eight tests and constructed a high-density genetic linkage map with resequencing-based 933,845 single-nucleotide polymorphism (SNP) markers covering a total genetic distance of 2483.17 cM. Nine quantitative trait loci (QTLs) for FOV7 resistance were identified, including qFOV7-D03-1 on chromosome D03 in two tests. Through a comparative analysis of gene expression and DNA sequence for predicted genes within the QTL region between the two parents and selected lines inoculated with FOV7, GB_D03G0217 encoding for a calmodulin (CaM)-like (CML) protein was identified as a candidate gene. A further analysis confirmed that the expression of GB_D03G0217 was suppressed, leading to increased disease severity in plants of the resistant parent with virus induced gene silencing (VIGS).

A Calmodulin-Like Gene (GbCML7) for Fiber Strength and Yield Improvement Identified by Resequencing Core Accessions of a Pedigree in Gossypium barbadense

Sea Island cotton (Gossypium barbadense) is world-renowned for its superior natural fiber. Although fiber strength is one of the most important fiber quality traits, genes contributing to fiber strength are poorly understood. Production of sea island cotton also is inextricably linked to improving its relatively low yield, thus enhancing the importance of joint improvement of both fiber quality and yield. We used genomic variation to uncover the genetic evidence of trait improvement resulting from pedigree breeding of Sea Island cotton. This pedigree was aimed at improving fiber strength and yielded an elite cultivar, XH35. Using a combination of genome-wide association study (GWAS) and selection screens, we detected 82 putative fiber-strength-related genes. Expression analysis confirmed a calmodulin-like gene, GbCML7, which enhanced fiber strength in a specific haplotype. This gene is a major-effect gene, which interacts with a minor-effect gene, GbTUA3, facilitating the enhancement of fiber strength in a synergistic fashion. Moreover, GbCML7 participates in the cooperative improvement of fiber strength, fiber length, and fiber uniformity, though a slight compromise exists between the first two of these traits and the latter. Importantly, GbCML7 is shown to boost yield in some backgrounds by increasing multiple yield components to varying degrees, especially boll number. Our work provides valuable genomic evidence and a key genetic factor for the joint improvement of fiber quality and yield in Sea Island cotton.

Chickpea Roots Undergoing Colonisation by Phytophthora medicaginis Exhibit Opposing Jasmonic Acid and Salicylic Acid Accumulation and Signalling Profiles to Leaf Hemibiotrophic Models

Hemibiotrophic pathogens cause significant losses within agriculture, threatening the sustainability of food systems globally. These microbes colonise plant tissues in three phases: a biotrophic phase followed by a biotrophic-to-necrotrophic switch phase and ending with necrotrophy. Each of these phases is characterized by both common and discrete host transcriptional responses. Plant hormones play an important role in these phases, with foliar models showing that salicylic acid accumulates during the biotrophic phase and jasmonic acid/ethylene responses occur during the necrotrophic phase. The appropriateness of this model to plant roots has been challenged in recent years. The need to understand root responses to hemibiotrophic pathogens of agronomic importance necessitates further research. In this study, using the root hemibiotroph Phytophthora medicaginis, we define the duration of each phase of pathogenesis in Cicer arietinum (chickpea) roots. Using transcriptional profiling, we demonstrate that susceptible chickpea roots display some similarities in response to disease progression as previously documented in leaf plant–pathogen hemibiotrophic interactions. However, our transcriptomic results also show that chickpea roots do not conform to the phytohormone responses typically found in leaf colonisation by hemibiotrophs. We found that quantified levels of salicylic acid concentrations in root tissues decreased significantly during biotrophy while jasmonic acid concentrations were significantly induced. This study demonstrated that a wider spectrum of plant species should be investigated in the future to understand the physiological changes in plants during colonisation by soil-borne hemibiotrophic pathogens before we can better manage these economically important microbes.

The hybrid lethality of interspecific F1 hybrids of Nicotiana: a clue to understanding hybrid inviability-a major obstacle to wide hybridization and introgression breeding of plants

Reproductive isolation poses a major obstacle to wide hybridization and introgression breeding of plants. Hybrid inviability in the postzygotic isolation barrier inevitably reduces hybrid fitness, consequently causing hindrances in the establishment of novel genotypes from the hybrids among genetically divergent parents. The idea that the plant immune system is involved in the hybrid problem is applicable to the intra- and/or interspecific hybrids of many different taxa. The lethality characteristics and expression profile of genes associated with the hypersensitive response of the hybrids, along with the suppression of causative genes, support the deleterious epistatic interaction of parental NB-LRR protein genes, resulting in aberrant hyper-immunity reactions in the hybrid. Moreover, the cellular, physiological, and biochemical reactions observed in hybrid cells also corroborate this hypothesis. However, the difference in genetic backgrounds of the respective hybrids may contribute to variations in lethality phenotypes among the parental species combinations. The mixed state in parental components of the chaperone complex (HSP90-SGT1-RAR1) in the hybrid may also affect the hybrid inviability. This review article discusses the facts and hypothesis regarding hybrid inviability, alongside the findings of studies on the hybrid lethality of interspecific hybrids of the genus Nicotiana. A possible solution for averting the hybrid problem has also been scrutinized with the aim of improving the wide hybridization and introgression breeding program in plants.

Effect of Calmodulin-like Gene (CML) Overexpression on Stilbene Biosynthesis in Cell Cultures of Vitis amurensis Rupr

Stilbenes are plant phenolics known to rapidly accumulate in grapevine and other plants in response to injury or pathogen attack and to exhibit a great variety of healing beneficial effects. It has previously been shown that several calmodulin-like protein (CML) genes were highly up-regulated in cell cultures of wild-growing grapevine Vitis amurensis Rupr. in response to stilbene-modulating conditions, such as stress hormones, UV-C, and stilbene precursors. Both CML functions and stilbene biosynthesis regulation are still poorly understood. In this study, we investigated the effect of overexpression of five VaCML genes on stilbene and biomass accumulation in the transformed cell cultures of V. amurensis. We obtained 16 transgenic cell lines transformed with the VaCML52, VaCML65, VaCML86, VaCML93, and VaCML95 genes (3–4 independent lines per gene) under the control of the double CaMV 35S promoter. HPLC-MS analysis showed that overexpression of the VaCML65 led to a considerable and consistent increase in the content of stilbenes of 3.8–23.7 times in all transformed lines in comparison with the control calli, while biomass accumulation was not affected. Transformation of the V. amurensis cells with other analyzed VaCML genes did not lead to a consistent and considerable effect on stilbene biosynthesis in the cell lines. The results indicate that the VaCML65 gene is implicated in the signaling pathway regulating stilbene biosynthesis as a strong positive regulator and can be useful in viticulture and winemaking for obtaining grape cultivars with a high content of stilbenes and stress resistance.

Calmodulin and calmodulin-like gene family in barley: Identification, characterization and expression analyses

Calmodulin (CaM) and calmodulin-like (CML) proteins are Ca²⁺ relays and play diverse and multiple roles in plant growth, development and stress responses. However, CaM/CML gene family has not been identified in barley (Hordeum vulgare). In the present study, 5 HvCaMs and 80 HvCMLs were identified through a genome-wide analysis. All HvCaM proteins possessed 4 EF-hand motifs, whereas HvCMLs contained 1 to 4 EF-hand motifs. HvCaM2, HvCaM3 and HvCaM5 coded the same polypeptide although they differed in nucleotide sequence, which was identical to the polypeptides coded by OsCaM1-1, OsCaM1-2 and OsCaM1-3. HvCaMs/CMLs were unevenly distributed over barley 7 chromosomes, and could be phylogenetically classified into 8 groups. HvCaMs/CMLs differed in gene structure, cis-acting elements and tissue expression patterns. Segmental and tandem duplication were observed among HvCaMs/CMLs during evolution. HvCML16, HvCML18, HvCML50 and HvCML78 were dispensable genes and the others were core genes in barley pan-genome. In addition, 14 HvCaM/CML genes were selected to examine their responses to salt, osmotic and low potassium stresses by qRT-PCR, and their expression were stress-and time-dependent. These results facilitate our understanding and further functional identification of HvCaMs/CMLs.

WIPK-NtLTP4 pathway confers resistance to Ralstonia solanacearum in tobacco

KEY MESSAGE

WIPK-NtLTP4 module improves the resistance to R. solanacearum via upregulating the expression of defense-related genes, increasing the antioxidant enzyme activity, and promoting stomatal closure in tobacco. Lipid transfer proteins (LTPs) are a class of small lipid binding proteins that play important roles in biotic and abiotic stresses. The previous study revealed that NtLTP4 positively regulates salt and drought stresses in Nicotiana tabacum. However, the role of NtLTP4 in biotic stress, especially regarding its function in disease resistance remains unclear. Here, the critical role of NtLTP4 in regulating resistance to Ralstonia solanacearum (R. solanacearum), a causal agent of bacterial wilt disease in tobacco, was reported. The NtLTP4-overexpressing lines markedly improved the resistance to R. solanacearum by upregulating the expression of defense-related genes, increasing the antioxidant enzyme activity, and promoting stomatal closure. Moreover, NtLTP4 interacted with wound-induced protein kinase (WIPK; a homolog of MAPK3 in tobacco) and acted in a genetically epistatic manner to WIPK in planta. WIPK could directly phosphorylate NtLTP4 to positively regulate its protein abundance. Taken together, these results broaden the knowledge about the functions of the WIPK-NtLTP4 module in disease resistance and may provide valuable information for improving tobacco plant tolerance to R. solanacearum.

Inducible Enrichment of Osa-miR1432 Confers Rice Bacterial Blight Resistance through Suppressing OsCaML2

MicroRNAs (miRNAs) handle immune response to pathogens by adjusting the function of target genes in plants. However, the experimentally documented miRNA/target modules implicated in the interplay between rice and Xanthomonas oryzae pv. oryzae (Xoo) are still in the early stages. Herein, the expression of osa-miR1432 was induced in resistant genotype IRBB5, but not susceptible genotype IR24, under Xoo strain PXO86 attack. Overexpressed osa-miR1432 heightened rice disease resistance to Xoo, indicated by enhancive enrichment of defense marker genes, raised reactive oxygen species (ROS) levels, repressed bacterial growth and shortened leaf lesion length, whilst the disruptive accumulation of osa-miR1432 accelerated rice susceptibility to Xoo infection. Noticeably, OsCaML2 (LOC_Os03g59770) was experimentally confirmed as a target gene of osa-miR1432, and the overexpressing OsCaML2 transgenic plants exhibited compromised resistance to Xoo infestation. Our results indicate that osa-miR1432 and OsCaML2 were differently responsive to Xoo invasion at the transcriptional level and fine-tune rice resistance to Xoo infection, which may be referable in resistance gene discovery and valuable in the pursuit of improving Xoo resistance in rice breeding.

Seed priming with calcium chloride enhances wheat resistance against wheat aphid Schizaphis graminum Rondani

BACKGROUND

Calcium is an essential macronutrient for plant growth. Although it has been shown that exogenous Ca application can increase plant resistance to abiotic stress, little is known about its potential to enhance plant tolerance to biotic stress. Here, we investigated whether pretreatment of wheat (Triticum aestivum L.) seeds with calcium chloride (CaCl₂ ) improves plant resistance against wheat aphid (Schizaphis graminum Rondani). The developmental time, population size, feeding behavior of aphids on plants grown from CaCl₂ - and water-pretreated seeds, and plant defense responses to aphid attack were investigated.

RESULTS

Seed pretreatment with CaCl₂ extended aphid development time and reduced aphid population size and feeding efficiency. In addition, the pretreatment significantly increased the concentration of Ca²⁺ in wheat leaves, and upregulated expression levels of TaCaM genes and callose synthase genes (TaGSL2, TaGSL8, TaGSL10, TaGSL12, TaGSL19, TaGSL22 and TaGSL23). Callose concentration in the leaves of plants grown from CaCl₂ -pretreated seeds increased significantly upon aphid attack. Further, callose deposition was observed mainly in the phloem.

CONCLUSION

These results suggest that seed pretreatment with CaCl₂ primes the plant response against wheat aphid attack, leading to modulation of callose deposition in the phloem in response to aphid attack. © 2021 Society of Chemical Industry.

Comparative Transcriptome Analysis of Rice Resistant and Susceptible Genotypes to Xanthomonas oryzae pv. oryzae Identifies Novel Genes to Control Bacterial Leaf Blight

The bacterial leaf blight in rice caused by Xanthomonas oryzae pv. oryzae (Xoo) affects crop losses worldwide. In spite of developing resistant varieties by introgressing different Xa genes, the occurrence of diseases is evident. Here we report identification of several genes that are associated with improved plant immunity against Xoo in a resistant genotype BPT-5204 in comparison with susceptible genotype TN-1. The RNA sequencing information was developed to identify the genes that could provide durable resistance in rice. Xoo-resistant rice genotype BPT-5204 with Xa 5, 13 and 21 genes is compared with sensitive Taichung Native 1 (TN-1) to identify the genetic pathways and gene networks involved in resistance mechanisms. The higher levels of salicylic acid resulted in upregulation of many pathogenesis-related (PR) and redox protein encoding transcripts which resulted in higher hypersensitive response in BPT-5204. Many Serine/threonine protein kinase, leucine-rich repeat (LRR) transmembrane protein kinase, protein kinase family genes, Wall-associated kinase (WAK) were upregulated that resulted in activation of bZIP, WRKY, MYB, DOF and HSFs transcription factors that are associated with improved plant immunity. The study provided roles of many genes and their associated plant immunity pathways that can be used for developing resistant rice cultivars.

Identification of QTLs for Spot Blotch Resistance in Two Bi-Parental Mapping Populations of Wheat

Spot blotch (SB) disease caused by the hemibiotrophic pathogen Bipolaris sorokiniana inflicting major losses to the wheat grown in warm and highly humid areas of the Indian subcontinent, including Bangladesh, necessitates identification of QTLs stably expressing in Indian subcontinent conditions. Thus, two RIL mapping populations, i.e., WC (WUYA × CIANO T79) and KC (KATH × CIANO T79), were phenotyped at Dinajpur, Bangladesh for three consecutive years (2013-2015) and genotyped on a DArTseq genotyping by sequencing (GBS) platform at CIMMYT, Mexico. In both populations, quantitative inheritance along with transgressive segregation for SB resistance was identified. The identified QTLs were mostly minor and were detected on 10 chromosomes, i.e., 1A, 1B, 2A, 2B, 2D, 4B, 4D, 5A, 5D, and 7B. The phenotypic variation explained by the identified QTLs ranged from 2.3–15.0%, whereby QTLs on 4B (13.7%) and 5D (15.0%) were the largest in effect. The identified QTLs upon stacking showed an additive effect in lowering the SB score in both populations. The probable presence of newly identified Sb4 and durable resistance gene Lr46 in the identified QTL regions indicates the importance of these genes in breeding for SB resistance in Bangladesh and the whole of South Asia.

Late blight in tomato: insights into the pathogenesis of the aggressive pathogen Phytophthora infestans and future research priorities

This review provides insights into the molecular interactions between Phytophthora infestans and tomato and highlights research gaps that need further attention. Late blight in tomato is caused by the oomycota hemibiotroph Phytophthora infestans, and this disease represents a global threat to tomato farming. The pathogen is cumbersome to control because of its fast-evolving nature, ability to overcome host resistance and inefficient natural resistance obtained from the available tomato germplasm. To achieve successful control over this pathogen, the molecular pathogenicity of P. infestans and key points of vulnerability in the host plant immune system must be understood. This review primarily focuses on efforts to better understand the molecular interaction between host pathogens from both perspectives, as well as the resistance genes, metabolomic changes, quantitative trait loci with potential for improvement in disease resistance and host genome manipulation via transgenic approaches, and it further identifies research gaps and provides suggestions for future research priorities.

EgJUB1 and EgERF113 transcription factors as potential master regulators of defense response in Elaeis guineensis against the hemibiotrophic Ganoderma boninense

BACKGROUND

Hemibiotrophic pathogen such as the fungal pathogen Ganoderma boninense that is destructive to oil palm, manipulates host defense mechanism by strategically switching from biotrophic to necrotrophic phase. Our previous study revealed two distinguishable expression profiles of oil palm genes that formed the basis in deducing biotrophic phase at early interaction which switched to necrotrophic phase at a later stage of infection.

RESULTS

The present report is a continuing study from our previous published transcriptomic profiling of oil palm seedlings against G. boninense. We focused on identifying differentially expressed genes (DEGs) encoding transcription factors (TFs) from the same RNA-seq data; resulting in 106 upregulated and 108 downregulated TFs being identified. The DEGs are involved in four established defense-related pathways responsible for cell wall modification, reactive oxygen species (ROS)-mediated signaling, programmed cell death (PCD) and plant innate immunity. We discovered upregulation of JUNGBRUNNEN 1 (EgJUB1) during the fungal biotrophic phase while Ethylene Responsive Factor 113 (EgERF113) demonstrated prominent upregulation when the palm switches to defense against necrotrophic phase. EgJUB1 was shown to have a binding activity to a 19 bp palindromic SNBE1 element, WNNYBTNNNNNNNAMGNHW found in the promoter region of co-expressing EgHSFC-2b. Further in silico analysis of promoter regions revealed co-expression of EgJUB1 with TFs containing SNBE1 element with single nucleotide change at either the 5th or 18th position. Meanwhile, EgERF113 binds to both GCC and DRE/CRT elements promoting plasticity in upregulating the downstream defense-related genes. Both TFs were proven to be nuclear-localized based on subcellular localization experiment using onion epidermal cells.

CONCLUSION

Our findings demonstrated unprecedented transcriptional reprogramming of specific TFs potentially to enable regulation of a specific set of genes during different infection phases of this hemibiotrophic fungal pathogen. The results propose the intricacy of oil palm defense response in orchestrating EgJUB1 during biotrophic and EgERF113 during the subsequent transition to the necrotrophic phase. Binding of EgJUB1 to SNBE motif instead of NACBS while EgERF113 to GCC-box and DRE/CRT motifs is unconventional and not normally associated with pathogen infection. Identification of these phase-specific oil palm TFs is important in designing strategies to tackle or attenuate the progress of infection.

Extracellular Fragmented Self-DNA Is Involved in Plant Responses to Biotic Stress

A growing body of evidence indicates that extracellular fragmented self-DNA (eDNA), by acting as a signaling molecule, triggers inhibitory effects on conspecific plants and functions as a damage-associated molecular pattern (DAMP). To evaluate early and late events in DAMP-dependent responses to eDNA, we extracted, fragmented, and applied the tomato (Solanum lycopersicum) eDNA to tomato leaves. Non-sonicated, intact self-DNA (intact DNA) was used as control. Early event analyses included the evaluation of plasma transmembrane potentials (Vm), cytosolic calcium variations (Ca²⁺ _{cy t}), the activity and subcellular localization of both voltage-gated and ligand-gated rectified K⁺ channels, and the reactive oxygen species (ROS) subcellular localization and quantification. Late events included RNA-Seq transcriptomic analysis and qPCR validation of gene expression of tomato leaves exposed to tomato eDNA. Application of eDNA induced a concentration-dependent Vm depolarization which was correlated to an increase in (Ca²⁺)_cyt; this event was associated to the opening of K⁺ channels, with particular action on ligand-gated rectified K⁺ channels. Both eDNA-dependent (Ca²⁺)_cyt and K⁺ increases were correlated to ROS production. In contrast, application of intact DNA produced no effects. The plant response to eDNA was the modulation of the expression of genes involved in plant-biotic interactions including pathogenesis-related proteins (PRPs), calcium-dependent protein kinases (CPK1), heat shock transcription factors (Hsf), heat shock proteins (Hsp), receptor-like kinases (RLKs), and ethylene-responsive factors (ERFs). Several genes involved in calcium signaling, ROS scavenging and ion homeostasis were also modulated by application of eDNA. Shared elements among the transcriptional response to eDNA and to biotic stress indicate that eDNA might be a common DAMP that triggers plant responses to pathogens and herbivores, particularly to those that intensive plant cell disruption or cell death. Our results suggest the intriguing hypothesis that some of the plant reactions to pathogens and herbivores might be due to DNA degradation, especially when associated to the plant cell disruption. Fragmented DNA would then become an important and powerful elicitor able to trigger early and late responses to biotic stress.

Identification and Characterization of Plant-Interacting Targets of Tomato Spotted Wilt Virus Silencing Suppressor

Tomato spotted wilt virus (TSWV; species Tomato spotted wilt orthotospovirus) is an economically important plant virus that infects multiple horticultural crops on a global scale. TSWV encodes a non-structural protein NSs that acts as a suppressor of host RNA silencing machinery during infection. Despite extensive structural and functional analyses having been carried out on TSWV NSs, its protein-interacting targets in host plants are still largely unknown. Here, we systemically investigated NSs-interacting proteins in Nicotiana benthamiana via affinity purification and mass spectrometry (AP-MS) analysis. Forty-three TSWV NSs-interacting candidates were identified in N. benthamiana. Gene Ontology (GO) and protein–protein interaction (PPI) network analyses were carried out on their closest homologs in tobacco (Nicotiana tabacum), tomatoes (Solanum lycopersicum) and Arabidopsis (Arabidopsis thaliana). The results showed that NSs preferentially interacts with plant defense-related proteins such as calmodulin (CaM), importin, carbonic anhydrase and two heat shock proteins (HSPs): HSP70 and HSP90. As two major nodes in the PPI network, CaM and importin subunit α were selected for the further verification of their interactions with NSs via yeast two-hybrid (Y2H) screening. Our work suggests that the downstream signaling, transportation and/or metabolic pathways of host-NSs-interacting proteins may play critical roles in NSs-facilitated TSWV infection.

Transcriptome Analysis of Alternative Splicing Events Induced by Arbuscular Mycorrhizal Fungi (Rhizophagus irregularis) in Pea (Pisum sativum L.) Roots

Alternative splicing (AS), a process that enables formation of different mRNA isoforms due to alternative ways of pre-mRNA processing, is one of the mechanisms for fine-tuning gene expression. Currently, the role of AS in symbioses formed by plants with soil microorganisms is not fully understood. In this work, a comprehensive analysis of the transcriptome of garden pea (Pisum sativum L.) roots in symbiosis with arbuscular mycorrhiza was performed using RNAseq and following bioinformatic analysis. AS profiles of mycorrhizal and control roots were highly similar, intron retention accounting for a large proportion of the observed AS types (67%). Using three different tools (SUPPA2, DRIMSeq and IsoformSwitchAnalyzeR), eight genes with AS events specific for mycorrhizal roots of pea were identified, among which four were annotated as encoding an apoptosis inhibitor protein, a serine/threonine-protein kinase, a dehydrodolichyl diphosphate synthase, and a pre-mRNA-splicing factor ATP-dependent RNA helicase DEAH1. In pea mycorrhizal roots, the isoforms of these four genes with preliminary stop codons leading to a truncated ORFs were up-regulated. Interestingly, two of these four genes demonstrating mycorrhiza-specific AS are related to the process of splicing, thus forming parts of the feedback loops involved in fine-tuning of gene expression during mycorrhization.

HaCRT1 of Heterodera avenae Is Required for the Pathogenicity of the Cereal Cyst Nematode

Cereal cyst nematodes are sedentary biotrophic endoparasites that secrete effector proteins into plant tissues to transit normal cells into specialized feeding sites and suppress plant defenses. To understand the function of nematode effectors in Heterodera avenae, here, we identified a calreticulin protein HaCRT1, which could suppress the cell death induced by Bax when expressed in Nicotiana benthamiana. HaCRT1 is synthetized in the subventral gland cells of pre-parasitic second-stage nematodes. Real-time PCR assays indicated that the expression of HaCRT1 was highest in parasitic second-stage juveniles. The expression of an HaCRT1-RFP fusion in N. benthamiana revealed that it was localized in the endoplasmic reticulum of the plant cell. The ability of H. avenae infecting plants was significantly reduced when HaCRT1 was knocked down by RNA interference in vitro. Arabidopsis thaliana plants expressing HaCRT1 were more susceptible than wild-type plants to Pseudomonas syringae. The induction of defense-related genes, PAD4, WRKY33, FRK1, and WRKY29, after treatment with flg22 was suppressed in HaCRT1-transgenic plants. Also, the ROS accumulation induced by flg22 was reduced in the HaCRT1-transgenic plants compared to wild-type plants. HaCRT1 overexpression increased the cytosolic Ca²⁺ concentration in A. thaliana. These data suggested that HaCRT1 may contribute to the pathogenicity of H. avenae by suppressing host basal defense.

Transcriptional changes of Pacific oyster Crassostrea gigas reveal essential role of calcium signal pathway in response to CO2-driven acidification

There is increasing evidence that ocean acidification (OA) has a significant impact on marine organisms. However, the ability of most marine organisms to acclimate to OA and the underlying mechanisms are still not well understood. In the present study, whole transcriptome analysis was performed to compare the impacts of short- (7 days, named as short group) and long- (60 days, named as long group) term CO₂ exposure (pH 7.50) on Pacific oyster Crassostrea gigas. The responses of C. gigas to short- and long-term CO₂ exposure shared common mechanisms in metabolism, membrane-associated transportation and binding processes. Long-term CO₂ exposure induced significant expression of genes involved in DNA or RNA binding, indicating the activated transcription after long-term CO₂ exposure. Oysters in the short-term group underwent significant intracellular calcium variation and oxidative stress. In contrast, the intracellular calcium, ROS level in hemocytes and H₂O₂ in serum recovered to normal levels after long-term CO₂ exposure, suggesting the compensation of physiological status and mutual interplay between calcium and oxidative level. The compensation was supported by the up-regulation of a series of calcium binding proteins (CBPs) and calmodulins (CaMs) related signal pathway. The results provided valuable information to understand the molecular mechanism underlying the responses of Pacific oyster to the acidified ocean and might have implications for predicting the possible effects of global climate changes on oyster aquaculture.

The Grapevine Calmodulin-Like Protein Gene CML21 Is Regulated by Alternative Splicing and Involved in Abiotic Stress Response

Calmodulin-like proteins (CMLs) represent a large family of plant calcium sensor proteins involved in the regulation of plant responses to environmental cues and developmental processes. In the present work, we identified four alternatively spliced mRNA forms of the grapevine CML21 gene that encoded proteins with distinct N-terminal regions. We studied the transcript abundance of CML21v1, CML21v2, CML21v3, and CML21v4 in wild-growing grapevine Vitis amurensis Rupr. in response to desiccation, heat, cold, high salinity, and high mannitol stress using quantitative real-time RT-PCR. The levels of all four splice variants of VaCML21 were highly induced in response to cold stress. In addition, VaCML21v1 and VaCML21v2 forms were highly modulated by all other abiotic stress treatments. Constitutive expression of VaCML21v2 and VaCML21v4 improved biomass accumulation of V. amurensis callus cell cultures under prolonged low temperature stress. Heterologous expression of the grapevine CML21v2 and VaCML21v4 splice variants in Arabidopsis improved survival rates of the transgenic plants after freezing. The VaCML21v2 overexpression enhanced activation of the cold stress-responsive marker genes AtDREB1A and AtDREB2A, while VaCML21v4 overexpression—AtCOR47, AtRD29A, AtRD29B, and AtKIN1 genes after freezing stress in the transgenic Arabidopsis. The results indicate that the grapevine CML21 gene acts as a positive regulator in the plant response to cold stress. The detected variety of CML21 transcripts and their distinct transcriptional responses suggested that this expansion of mRNA variants could contribute to the diversity of grapevine adaptive reactions.

BcSas2-Mediated Histone H4K16 Acetylation Is Critical for Virulence and Oxidative Stress Response of Botrytis cinerea

Histone acetyltransferase plays a critical role in transcriptional regulation by increasing accessibility of target genes to transcriptional activators. Botrytis cinerea is an important necrotrophic fungal pathogen with worldwide distribution and a very wide host range, but little is known of how the fungus regulates the transition from saprophytic growth to infectious growth. Here, the function of BcSas2, a histone acetyltransferase of B. cinerea, was investigated. Deletion of the BcSAS2 gene resulted in significantly reduced acetylation levels of histone H4, particularly of H4K16ac. The deletion mutant ΔBcSas2.1 was not only less pathogenic but also more sensitive to oxidative stress than the wild-type strain. RNA-Seq analysis revealed that a total of 13 B. cinerea genes associated with pathogenicity were down-regulated in the ΔBcSas2.1 mutant. Independent knockouts of two of these genes, BcXYGA (xyloglucanase) and BcCAT (catalase), led to dramatically decreased virulence and hypersensitivity to oxidative stress, respectively. Chromatin immunoprecipitation followed by quantitative PCR confirmed that BcSas2 bound directly to the promoter regions of both these pathogenicity-related genes. These observations indicated that BcSas2 regulated the transcription of pathogenicity-related genes by controlling the acetylation level of H4K16, thereby affecting the virulence and oxidative sensitivity of B. cinerea.

The overexpression of OsACBP5 protects transgenic rice against necrotrophic, hemibiotrophic and biotrophic pathogens

The most devastating diseases in rice (Oryza sativa) are sheath blight caused by the fungal necrotroph Rhizoctonia solani, rice blast by hemibiotrophic fungus Magnaporthe oryzae, and leaf blight by bacterial biotroph Xanthomonas oryzae (Xoo). It has been reported that the Class III acyl-CoA-binding proteins (ACBPs) such as those from dicots (Arabidopsis and grapevine) play a role in defence against biotrophic pathogens. Of the six Arabidopsis (Arabidopsis thaliana) ACBPs, AtACBP3 conferred protection in transgenic Arabidopsis against Pseudomonas syringae, but not the necrotrophic fungus, Botrytis cinerea. Similar to Arabidopsis, rice possesses six ACBPs, designated OsACBPs. The aims of this study were to test whether OsACBP5, the homologue of AtACBP3, can confer resistance against representative necrotrophic, hemibiotrophic and biotrophic phytopathogens and to understand the mechanisms in protection. Herein, when OsACBP5 was overexpressed in rice, the OsACBP5-overexpressing (OsACBP5-OE) lines exhibited enhanced disease resistance against representative necrotrophic (R. solani & Cercospora oryzae), hemibiotrophic (M. oryzae & Fusarium graminearum) and biotrophic (Xoo) phytopathogens. Progeny from a cross between OsACBP5-OE9 and the jasmonate (JA)-signalling deficient mutant were more susceptible than the wild type to infection by the necrotroph R. solani. In contrast, progeny from a cross between OsACBP5-OE9 and the salicylic acid (SA)-signalling deficient mutant was more susceptible to infection by the hemibiotroph M. oryzae and biotroph Xoo. Hence, enhanced resistance of OsACBP5-OEs against representative necrotrophs appears to be JA-dependent whilst that to (hemi)biotrophs is SA-mediated.

Plant-Pathogen Interactions: Broad Mite (Polyphagotarsonemus latus)-Induced Proteomic Changes in Chili Pepper Plant (Capsicum frutescens)

Plant-pathogen interactions are key biological events that shape ecological dynamics, food production, agriculture and economy. In this context, Capsicum frutescens is an economically and culturally significant chili pepper plant grown widely across the globe as an essential ingredient of hot sauces, chili concentrates, oleoresin flavors, and also in traditional medicines. An important pathogen that limits chili cultivation causing low yield and economic loss is the broad mite, Polyphagotarsonemus latus. Broad mite-infested chili plants have stunted growth and leaves appear coppery and dark, which show symptoms of leaf curl and more importantly the smaller fruits unfit for consumption. The molecular mechanisms of how broad mite affect chili remain poorly understood. In this study, we report a tandem mass tag (TMT)-labeled mass spectrometry-based quantitative proteomic analysis of leaves and apical meristems of healthy and infected chili pepper plants. In total, we identified 5799 proteins, of which 1677 proteins were found to be differentially regulated in infested plants. Related signaling pathways of the differentially expressed proteins were examined using bioinformatics tools. Predominantly, we identified pathways associated with jasmonic acid synthesis, mitogen-activated protein kinase, and plant defense and hormone signal transduction. We also observed upregulation of several enzymes of the phenylpropanoid and carotenoid biosynthetic pathways. This study provides the first in-depth proteomic analysis that correlates broad mite infestation in chili and dysregulation of various pathways that take part in plant defense. In the future, data can be extrapolated for innovation in pest management methods whose ecological footprints are better understood.

Interaction Between AtCML9 and AtMLO10 Regulates Pollen Tube Development and Seed Setting

In higher-plant reproduction, the compatibility of pollen tube germination in the pistil is essential for successful double fertilization. It has been reported that Mildew Locus O (MLO) family gene NTA (MLO7), expressing in synergid cells, can correctly guide pollen tubes. However, the molecular mechanism underlying the interacting partners to MLOs in the fertilization is still unknown. In our study, we identified the direct protein interaction between CML9 and MLO10 within a non-canonical CaMBD. In GUS reporter assays, CML9 expresses in a high level in pollens, whereas MLO10 can be specifically detected in stigma which reaches up to a peaking level before fertilization. Therefore, the spatio-temporal expression patterns of MLO10 and CML9 are required for the time-window of pollination. When we observed the pollen germination in vitro, two cml9 mutant alleles dramatically reduced germination rate by 15% compared to wild-type. Consistently, the elongation rate of pollen tubes in planta was obviously slow while manually pollinating cml9-1 pollens to mlo10-1 stigmas. Additionally, cml9-1 mlo10-1 double mutant alleles had relatively lower rate of seed setting. Taken together, protein interaction between MLO10 and CML9 is supposed to affect pollen tube elongation and further affect seed development.