OsMPK3 positively regulates the JA signaling pathway and plant resistance to a chewing herbivore in rice

Key message

Silencing OsMPK3 decreased elicited JA levels, which subsequently reduced levels of herbivore-induced trypsin protease inhibitors (TrypPIs) and improved the performance of SSB larvae, but did not influence BPH.

Abstract

Mitogen-activated protein kinases (MPKs) are known to play an important role in plant defense by transferring biotic and abiotic signals into programmed cellular responses. However, their functions in the herbivore-induced defense response in rice remain largely unknown. Here, we identified a MPK3 gene from rice, OsMPK3, and found that its expression levels were up-regulated in response to infestation by the larvae of the striped stem borer (SSB) (Chilo suppressalis), to mechanical wounding and to treatment with jasmonic acid (JA), but not to infestation by the brown planthopper (BPH) Nilaparvata lugens or to treatment with salicylic acid. Moreover, mechanical wounding and SSB infestation induced the expression of OsMPK3 strongly and quickly, whereas JA treatment induced the gene more weakly and slowly. Silencing OsMPK3 (ir-mpk3) reduced the expression of the gene by 50–70 %, decreased elicited levels of JA and diminished the expression of a lipoxygenase gene OsHI-LOX and an allene oxide synthase gene OsAOS1. The reduced JA signaling in ir-mpk3 plants decreased the levels of herbivore-induced trypsin protease inhibitors (TrypPIs) and improved the performance of SSB larvae, but did not influence BPH. Our findings suggest that the gene OsMPK3 responds early in herbivore-induced defense and can be regulated by rice plants to activate a specific and appropriate defense response to different herbivores.     

OsNPR1 negatively regulates herbivore‐induced JA and ethylene signaling and plant resistance to a chewing herbivore in rice

NPR1 (a non‐expressor of pathogenesis‐related genes1) has been reported to play an important role in plant defense by regulating signaling pathways. However, little to nothing is known about its function in herbivore‐induced defense in monocot plants. Here, using suppressive substrate hybridization, we identified a NPR1 gene from rice, OsNPR1, and found that its expression levels were upregulated in response to infestation by the rice striped stem borer (SSB) Chilo suppressalis and rice leaf folder (LF) Cnaphalocrocis medinalis, and to mechanical wounding and treatment with jasmonic acid (JA) and salicylic acid (SA). Moreover, mechanical wounding induced the expression of OsNPR1 quickly, whereas herbivore infestation induced the gene more slowly. The antisense expression of OsNPR1 (as‐npr1), which reduced the expression of the gene by 50%, increased elicited levels of JA and ethylene (ET) as well as of expression of a lipoxygenase gene OsHI‐LOX and an ACC synthase gene OsACS2. The enhanced JA and ET signaling in as‐npr1 plants increased the levels of herbivore‐induced trypsin proteinase inhibitors (TrypPIs) and volatiles, and reduced the performance of SSB. Our results suggest that OsNPR1 is an early responding gene in herbivore‐induced defense and that plants can use it to activate a specific and appropriate defense response against invaders by modulating signaling pathways.     

Expression and characteristics of rice xylanase inhibitor OsXIP,a member of a new class of antifungal proteins

It has been hypothesized that xylanase inhibitors play important roles in plant defense against microbial pathogens. Currently, there is little information available about xylanase inhibitor OsXIP in rice and its gene expression. We cloned a xylanase inhibitor gene OsXIP from rice (Oryza sativa L. cv. Nipponbare) genomic DNA. To determine the function of OsXIP, we generated OsXIP-overexpressing transgenic rice plants. The transgenic plants had significantly higher OsXIP expression and showed enhanced defense response to Magnaporthe oryzae compared to the wild-type plants. The results also showed that the increased OsXIP expression was accompanied by the up-regulation of pathogenesisrelated genes. To clarify the OsXIP expression pattern, a ProOsXIP::GUS vector was constructed and transgenic plants were obtained. GUS staining results revealed that OsXIP showed organ-specific expressions in rice plants. OsXIP was primarily expressed in the roots and in the veins, but it was weakly expressed in the leaves. Analyses of the OsXIP expression in response to biotic and abiotic stresses indicated that it was drastically induced by biotic stresses and methyl jasmonate treatment. OsXIP, a member of a new class of antifungal proteins, may function as a barrier that prevents the cell wall degradation by xylanases excreted by fungal pathogens. The OsXIP was found to be a stressresponsive gene and it could take part in plant defense via a JA-mediated signaling pathway.     

Root nematode infection enhances leaf defense against whitefly in tomato

The foliar response to different herbivores sharing the same hosts is an important topic for the study of plant-insect interactions. Plants evolve local and systemic resistant strategies to cope with herbivores. Many researchers have characterized the mechanisms of leaf responses to insect infestation; however, the fact that roots serve as systemic resistance modulators to leaf herbivores has been widely ignored. Here, we report that tomato (Solanum lycopersicum) plants infected with southern root-knot nematodes (Meloidogyne incognita)—which feed on the roots to form nodules—enhanced leaf defenses against aboveground attackers, specifically, the whitefly (Bemisia tabaci). Our results show that nematode infection reduced the whitefly population abundance because of conferring a stronger SA-dependent defense pathway against whitefly than in tomato plants without nematode infection. Meanwhile, nematode-infected tomato plant also activated the foliar JA-dependent defense pathway at 4 h after whitefly infestation. However, the foliar JA-dependent defense under whitefly infestation alone was suppressed, with the JA content being nearly 30 % lower than that in tomato plants co-infected with nematodes and whiteflies. Furthermore, nematode infection significantly decreased the plant nitrogen concentration in leaves and roots. As a result, nematode infection reduced the number of whiteflies by enhancing foliar SA-dependent defense, activating JA-dependent defense and decreasing nitrogen nutrition. Our results suggest that underground nematode infection significantly enhances the defense ability of tomato plants against whitefly.     

Herbivore- and Elicitor- Induced Resistance in Groundnut to Asian armyworm,Spodoptera litura (Fab.) (Lepidoptera: Noctuidae)

Induced defense was studied in three groundnut genotypes ICGV 86699 (resistant), NCAc 343 (resistant) and TMV 2 (susceptible) in response to Spodoptera litura infestation and jasmonic acid (JA) application. The activity of the oxidative enzymes [peroxidase (POD) and polyphenol oxidase (PPO)] and the amounts other host plant defense components [total phenols, hydrogen peroxide (H2O2), malondialdehyde (MDA), and protein content] were recorded at 24, 48, 72 and 96 h in JA pretreated (one day before) plants and infested with S. litura, and JA application and simultaneous infestation with S. litura to understand the defense response of groundnut genotypes against S. litura damage. Data on plant damage, larval survival and larval weights were also recorded. There was a rapid increase in the activities of POD and PPO and in the quantities of total phenols, H2O2, MDA and protein content in the JA pretreated + S. litura infested plants. All the three genotypes showed quick response to JA application and S. litura infestation by increasing the defensive compounds. Among all the genotypes, higher induction was recorded in ICGV 86699 in most of the parameters. Reduced plant damage, low larval survival and larval weights were observed in JA pretreated plants. It suggests that pretreatment with elicitors, such as JA could provide more opportunity for plant defense against herbivores.     

二化螟与稻纵卷叶螟幼虫取食诱导的水稻挥发物比较

前期研究结果表明,二化螟和稻纵卷叶螟幼虫为害所诱导的水稻挥发物能对二化螟绒茧蜂Apanteles chilonis Munakata、二化螟Chilo suppressalis(Walker)和稻纵卷叶螟Cnaphalocrocis medinalis(Guene)雌成虫的行为产生影响,并且两者的影响效应存在明显差异,但至今仍不清楚2种害虫危害后水稻挥发物的变化情况。利用动态吸附法对健康水稻苗、二化螟或稻纵卷叶螟幼虫为害苗的挥发物进行捕集与鉴定。在3种处理水稻苗中,共捕集到28种挥发物组分,包括萜类化合物、烷烃类化合物、酮类、醇类、水杨酸甲酯和一些未知化合物。二化螟和稻纵卷叶螟为害均能导致水稻挥发物总量和大多挥发物组分释放量的上升;同时,二化螟幼虫危害能诱导水稻新释放2-heptanonol,(E)-linalooloxide和2种未知挥发物组分,稻纵卷叶螟为害则可诱导水稻产生2-heptanonol,(E)-linalooloxide,MeSA和β-caryophyllene4种新化合物。2种虫害稻株间的比较表明,β-caryophyllene和MeSA是稻纵卷叶螟危害水稻后诱导产生的特有挥发物组分,并且linalool,α-copaene,(+)-cedrol,n-heptadecane和n-nonadecane在二化螟为害苗与稻纵卷叶螟为害苗之间差异显著。这一结果也许可以解释2种害虫诱导水稻挥发物对天敌和害虫行为影响不同的原因。     

Two novel protein kinase genes,OsMSRPK1 andOsMSURPK2, are regulated by diverse environmental stresses in rice

Two novel rice (Oryza sativa L.) protein kinase (PK) genes have been isolated.OsMSRPK1 andOsMSURPK2, which most likely exist as single-copy genes in the rice genome, encode 693 and S03 amino acids polypeptide, respectively, and have the serine/threonine kinase domain of cyclin dependent protein kinase (OsMSRPK1), or the serine/threonine kinase domain and NAF domain (OsMSURPK2). Steady-state mRNA analyses of these PKs, with constitutive expression in the leaves of two-week-old seedlings, revealed thatOsMSRPK1 is up-regulated upon exposure to environmental stresses, whereasOsMSVRPK2 is down-regulated by these same stresses. Furthermore, the two PKs are developmentally regulated in both young and mature rice plants, including in the panicles. These results strongly suggest that the genes have roles in both plant development and in their defense/stress-signaling pathways.     

Characterization of a xylanase inhibitor TAXI-I from wheat

Xylanase inhibitor TAXI-I gene was cloned from wheat (Triticum aestivum L.) and then TAXI-I encoding sequence was expressed in Escherichia coli. The recombinant TAXI-I protein inhibited glycoside hydrolase (GH) family 11 xylanases in Aspergillus niger (Anx; a fungal xylanase), and Thermomonospora fusca (Tfx; a bacterial xylanase), and also inhibited hybrid xylanases Atx (a hybrid xylanase whose parents are T. fusca and A. niger) and Btx (a hybrid xylanase whose parents are T. fusca and Bacillus subtilis). Among the tested xylanases, A. niger xylanase was the most inhibited one by wheat xylanase inhibitor TAXI-I, while T. fusca xylanase was the least inhibited one. The profile of TAXI-I gene expression in wheat in response to phytohormones was also investigated. TAXI-I gene expression was drastically induced by methyl jasmonate (MeJa), and hardly detected in gibberellic acid (GA) treatment. Therefore, TAXI-I might be involved in plant defense against fungal and bacteria xylanases.     

RNAi-mediated knockdown of the XIP-type endoxylanase inhibitor gene, OsXIP, has no effect on grain development and germination in rice

OsXIP (Oryza sativa xylanase inhibitor protein) is a XIP-type xylanase inhibitor which was identified as a protein encoded by a wound stress-responsive gene in rice. Although the OsXIP gene was specifically expressed in mature grains under basal conditions, recombinant OsXIP had no effect on rice endogenous xylanases, and OsXIP-suppressed transgenic rice plants did not exhibit any change in grain development and germination, suggesting that rice development may be independent of OsXIP. Analysis using an OsXIP-specific antibody revealed that OsXIP is markedly accumulated in apoplast in rice root cells by wounding. These results reinforced the possibility that OsXIP is involved in plant defense mechanisms against phytopathogens.     

Role of SIRT1 in Streptococcus pneumoniae-induced human β-defensin-2 and interleukin-8 expression in A549 cell

Streptococcus pneumoniae is an important pathogen of pneumonia in human. Human alveolar epithelium acts as an effective barrier and is an active participant in host defense against invasion of bacterial by production of various mediators. Sirtuin 1 (SIRT1), the prototypic class III histone deacetylase, is involved in the molecular control of lifespans and immune responses. This study aimed at examining the role of SIRT1 in mediating S. pneumoniae-induced human β-defensin-2 (hBD2) and interleukin-8(IL-8) expression in the alveolar epithelial cell line A549 and the underlying mechanisms involved. A549 cells were infected with S. pneumoniae for indicated times. Exposure of A549 cells to S. pneumoniae increased the expressions of SIRT1 protein, hBD2 and IL-8 mRNA, and protein. The SIRT1 activator resveratrol enhanced S. pneumoniae-induced gene expression of hBD2 but decreased IL-8 mRNA levels. Blockade of SIRT1 activity by the SIRT1 inhibitors nicotinamide reduced S. pneumoniae-induced hBD2 mRNA expression but increased its stimulatory effects on IL-8 mRNA. S. pneumoniae-induced activation of extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase (MAPK). SIRT1 expression was attenuated by selective inhibitors of ERK and p38 MAPK. The hBD2 mRNA production was decreased by pretreatment with p38 MAPK inhibitor but not with ERK inhibitor, whereas the IL-8 mRNA expression was controlled by phosphorylation of ERK. These results suggest that SIRT1 mediates the induction of hBD2 and IL-8 gene expression levels in A549 cell by S. pneumoniae. SIRT1 may play a key role in host immune and defense response in A549.     

Interrelationship of Gene Expression, Polysome Prevalence, and Respiration during Ripening of Ethylene and/or Cyanide-Treated Avocado Fruit

Upon initiation of ripening in avocado fruit (Persea americana Mill. cv Hass) with 10 microliters/liter ethylene, polysome prevalence and associated poly(A)⁺ mRNA increase approximately 3-fold early in the respiratory climacteric and drop off to preclimacteric levels at the peak of the respiratory climacteric. The increase in poly(A)⁺ mRNA on polysomes early in the respiratory climacteric constitutes a generic increase in constitutive mRNAs. New gene expression associated with ripening is minimal but evident after 10 hours of ethylene treatment and continues to increase relative to constitutive gene expression throughout the climacteric. The respiratory climacteric can be temporally separated into two phases. The first phase is associated with a general increase in protein synthesis, whereas the second phase reflects new gene expression and accumulation of corresponding proteins which may be responsible for softening and other ripening characteristics. A major new message on polysomes that arises concomitantly with the respiratory climacteric codes for an in vitro translation product of 53 kilodaltons which is immunoprecipitated by antiserum against avocado fruit cellulase.

Cyanide at 500 microliters/liter fails to affect the change in polysome prevalance or new gene expression associated with the ethylene-evoked climacteric in avocado fruit. Treatment of fruit with 500 microliters/liter cyanide alone initiates a respiratory increase within 4 hours, ethylene biosynthesis within 18 hours, and new gene expression akin to that educed by ethylene within 20 hours of exposure to cyanide.