Search

Complete panicle exsertion (CPE) is an economically important quantitative trait that contributes to grain yield in rice. We deployed an integrated approach for understanding the molecular mechanism of CPE using a stable ethyl methanesulfonate mutant line, CPE-109 of the Samba Mahsuri (SM) variety of rice (Oryza sativa), which exhibits CPE. Two consistent genomic regions were identified for CPE through quantitative trait locus (QTL) mapping [ qCPE-4 (28.24–31.22 Mb) and qCPE-12 (2.30–3.18 Mb)] and QTL-sequencing [chr 4 (31.21–33.69 Mb) and chr 12 (0.12–3.15 Mb)]. Two non-synonymous single nucleotide polymorphisms, namely KASP 12–12 (T→C; chr12:1269983) in Os12g0126300 , encoding an AP2/ERF transcription factor, and KASP 12–16 (G→A; chr12:1515198) in Os12g0131400 , encoding an F-box domain-containing protein, explained 81.05% and 59.61% of the phenotypic variance, respectively, and exhibited strong co-segregation with CPE in F2 mapping populations, advanced generation lines, and CPE-exhibiting SM mutants through KASP assays. Down-regulation of these genes in CPE-109 compared with SM (wild type) was observed in transcriptome sequencing of flag leaves, which was validated through qRT-PCR. We propose that the abrogation of Os12g0126300 and Os12g0131400 in CPE-109 combinatorially influences down-regulation of ethylene biosynthetic genes, Os01g0192900 (ACC synthase) and Os05g0497300 (ethylene-responsive factor-2), and up-regulation of a gibberellic acid synthetic gene, Os06g0569900 (ent-kaurene synthase) and the two cytokinin biosynthetic genes Os07g0486700 (cytokinin- O -glucosyltransferase 2) and Os10g0479500 (similar to carboxy-lyase), which results in complete panicle exsertion. [ABSTRACT FROM AUTHOR]

Historically, Xanthomonas species are primarily known for their pathogenicity against plants, but recently, there have been more findings of non-pathogenic xanthomonads. In the present study, we report isolates from healthy rice seeds that belong to a new species, Xanthomonas protegens , a protector of the rice plants against a serious pathogenic counterpart, i.e. X. oryzae pv. oryzae upon leaf clip co-inoculation. The new member species is non-pathogenic to rice and lacks a type III secretion system. The pangenome investigation revealed a large number of unique genes, including a novel lipopolysaccharide biosynthetic gene cluster, that might be important in its adaptation. The phylo-taxonogenomic analysis revealed that X. protegens is a taxonomic outlier species of X. sontii , a core, vertically transmitted rice seed endophyte with numerous probiotic properties. Interestingly, X. sontii is also reported as a keystone species of healthy rice seed microbiome. The findings and resources will help in the development of unique gene markers and evolutionary studies of X. sontii as a successful symbiont and X. oryzae as a serious pathogen. Here, we propose X. protegens sp. nov. as a novel species of the genus Xanthomonas with PPL118 = MTCC 13396 = CFBP 9164 = ICMP 25181 as the type strain. PPL117, PPL124, PPL125, and PPL126 are other strains of the species. [ABSTRACT FROM AUTHOR]

Cellobiosidase (CbsA) is an important secreted virulence factor of Xanthomonas oryzae pv. oryzae (Xoo), which causes bacterial blight of rice. CbsA is one of several cell wall‐degrading enzymes secreted by Xoo via the type II secretion system (T2SS). CbsA is considered a fundamental virulence factor for vascular pathogenesis. CbsA has an N‐terminal glycosyl hydrolase domain and a C‐terminal fibronectin type III (FnIII) domain. Interestingly, the secreted form of CbsA lacks the FnIII domain during in planta growth. Here we show that the presence of the FnIII domain inhibits the enzyme activity of CbsA on polysaccharide substrates like carboxymethylcellulose. The FnIII domain is required for the interaction of CbsA with SecB chaperone, and this interaction is crucial for the stability and efficient transport of CbsA across the inner membrane. Deletion of the FnIII domain reduced virulence similar to ΔcbsA Xoo, which corroborates the importance of the FnIII domain in CbsA. Our work elucidates a hitherto unknown function of the FnIII domain in enabling the virulence‐promoting activity of CbsA. [ABSTRACT FROM AUTHOR]

Effectors that suppress effector‐triggered immunity (ETI) are an essential part of the arms race in the co‐evolution of bacterial pathogens and their host plants. Xanthomonas oryzae pv. oryzae uses multiple type III secretion system (T3SS) secreted effectors such as XopU, XopV, XopP, XopG, and AvrBs2 to suppress rice immune responses that are induced by the interaction of two other effectors, XopQ and XopX. Here we show that each of these five suppressors can interact individually with both XopQ and XopX. One of the suppressors, XopG, is a predicted metallopeptidase that appears to have been introduced into X. oryzae pv. oryzae by horizontal gene transfer. XopQ and XopX interact with each other in the nucleus while interaction with XopG sequesters them in the cytoplasm. The XopG E76A and XopG E85A mutants are defective in interaction with XopQ and XopX, and are also defective in suppression of XopQ–XopX‐mediated immune responses. Both mutations individually affect the virulence‐promoting ability of XopG. These results indicate that XopG is important for X. oryzae pv. oryzae virulence and provide insights into the mechanisms by which this protein suppresses ETI in rice. [ABSTRACT FROM AUTHOR]

SUMMARY: Xanthomonas oryzae pv. oryzae uses several type III secretion system (T3SS) secreted effectors, namely XopN, XopQ, XopX and XopZ, to suppress rice immune responses that are induced following treatment with cell wall degrading enzymes. Here we show that a T3SS secreted effector XopX interacts with two of the eight rice 14‐3‐3 proteins. Mutants of XopX that are defective in 14‐3‐3 binding are also defective in suppression of immune responses, suggesting that interaction with 14‐3‐3 proteins is required for suppression of host innate immunity. However, Agrobacterium‐mediated delivery of both XopQ and XopX into rice cells results in induction of rice immune responses. These immune responses are not observed when either protein is individually delivered into rice cells. XopQ‐XopX‐induced rice immune responses are not observed with a XopX mutant that is defective in 14‐3‐3 binding. Yeast two‐hybrid, bimolecular fluorescence complementation and co‐immunoprecipitation assays indicate that XopQ and XopX interact with each other. A screen for Xanthomonas effectors that can suppress XopQ‐XopX‐induced rice immune responses led to the identification of five effectors, namely XopU, XopV, XopP, XopG and AvrBs2, that could individually suppress these immune responses. These results suggest a complex interplay of Xanthomonas T3SS effectors in suppression of both pathogen‐triggered immunity and effector‐triggered immunity to promote virulence on rice. Significance Statement: This work studies the role of the type III effector XopX in the suppression and induction of rice immune responses, by differential interaction with either 14‐3‐3 proteins, or with the type III effector XopQ respectively. We have also identified a subset of type III effectors which can suppress XopQ‐XopX induced immune responses. [ABSTRACT FROM AUTHOR]

Summary: Many bacterial phytopathogens employ effectors secreted through the type‐III secretion system to suppress plant innate immune responses. The Xanthomonas type‐III secreted non‐TAL effector protein Xanthomonas outer protein Q (XopQ) exhibits homology to nucleoside hydrolases. Previous work indicated that mutations which affect the biochemical activity of XopQ fail to affect its ability to suppress rice innate immune responses, suggesting that the effector might be acting through some other pathway or mechanism. In this study, we show that XopQ interacts in yeast and in planta with two rice 14‐3‐3 proteins, Gf14f and Gf14g. A serine to alanine mutation (S65A) of a 14‐3‐3 interaction motif in XopQ abolishes the ability of XopQ to interact with the two 14‐3‐3 proteins and to suppress innate immunity. Surprisingly, the S65A mutant gains the ability to interact with a third 14‐3‐3 protein that is a negative regulator of innate immunity. The XopQS65A mutant is an inducer of rice immune responses and this property is dominant over the wild‐type function of XopQ. Taken together, these results suggest that XopQ targets the rice 14‐3‐3 mediated immune response pathway and that its differential phosphorylation might enable interaction with alternative 14‐3‐3 proteins. [ABSTRACT FROM AUTHOR]

Asub-groupofLuxRfamilyofproteinsthatplaysimportantrolesinquorumsensing,aprocessofcell-cellcommunication,iswidespreadinproteobacteria.TheseproteinshaveatypicalmodularstructureconsistingofN-terautoinducerbindingandC-terhelix-turn-helix(HTH)DNAbindingdomains.TheautoinducerbindingdomainrecognizessignalingmoleculeswhicharemostoftenN-acylhomoserinelactones(AHLs)butcouldalsobeothernovelandyetunidentifiedmolecules.Inthisstudywecarriedoutaseriesofspecificdomainswappingandpromoteractivationexperimentsasafirststeptoengineersyntheticsignalingmodules,takingadvantageofthemodularityandtheversatile/diversesignalspecificitiesofLuxRproteins.InourexperimentstheN-terdomainsfromdifferentLuxRhomologswereeitherinterchangedorplacedintandemfollowedbyaC-terdomain.Therationaldesignofthehybridproteinswassupportedbyastructure-basedhomologymodelingstudiesofthreemembersoftheLuxRfamily(i.e.,LasR,RhlR,andOryRbeingchosenfortheiruniqueligandbindingspecificities)andofselectedchimeras.OurresultsrevealthattheseLuxRhomologswereabletoactivatepromoterelementsthatwerenottheirusualtargets;wealsoshowthathybridLuxRproteinsretainedtheabilitytorecognizethesignalspecificfortheirN-terautoinducerbindingdomain.However,theactivityofhybridLuxRproteinscontainingtwoAHLbindingdomainsintandemappearstodependontheorganizationandnatureoftheintroduceddomains.ThisstudyrepresentsadvancesintheunderstandingofthemodularityofLuxRproteinsandprovidesadditionalpossibilitiestousehybridproteinsinbothbasicandappliedsyntheticbiologybasedresearch. [ABSTRACT FROM AUTHOR]

A future challenge will be understanding the extensive communication that most likely takes place in bacterial interspecies and interkingdom signaling between plants and bacteria. A major bacterial inter-cellular signaling system in Gram-negative bacteria is LuxI/R quorum sensing (QS) based on the production (via the LuxI-family proteins) and detection (via the LuxR-family proteins) of N-acyl homoserine lactones (AHLs) signaling molecules. LuxR proteins which have the same modular structure of QS LuxRs but are devoid of a cognate LuxI AHL synthase are called solos. LuxR solos have been shown to be responsible to respond to exogenous AHLs produced by neighboring cells as well endogenously produced AHLs. It is now also evident that some LuxR proteins have evolved from the ability to binding AHLs and respond to other molecules/signals. For example, recent research has shown that a sub-family of LuxR solos responds to small molecules produced by plants. This indicates the presence of a uni-directional interkingdom signaling system occurring from plants to bacteria. In addition LuxR solos have now been also implicated to respond to endogenously produced signals which are not AHLs. In this Mini Review article we will discuss current trends and implications of the role of LuxR solos in bacterial responses to other signals using proteins related to AHL QS systems. [ABSTRACT FROM AUTHOR]

This article intends to give a narrative account of Hindi Movement in Bihar. It argues that the pro-Hindi campaigns should not be studied only as a campaign for democratic rights of Hindi speaking people of Bihar. It was an ideological movement. It started with a moderate stance but soon it turned into a hostile anti-Urdu campaign. The Hindi Movement was a significant movement in the sense that it united a large number of Hindi intelligentsia throughout Northern and Eastern India. In Bihar, unlike the United Provinces, Hindi was introduced as the court language without much resistance in 1880. This movement received support from the government officials (Campbell and others), Bengali newspapers (Bengalee and others), powerful Hindu landlords (Darbhanga Maharaj and others), organisations like Hindi Pracharini Sabha, Hindi press ( Khadagvilas Press) and contemporary Hindi newspapers like Bihar Bandhu. It was not that the claims of Hindi supporters were not opposed by the supporters of Urdu in Bihar but the opposition slowed down as it became evident that the Government was bent on introducing Nagari script, the main demand of Hindi movement supporters. [ABSTRACT FROM PUBLISHER]

Xanthomonas species are major pathogens of plants and have been studied extensively. There is increasing recognition of the importance of non-pathogenic species within the same genus. With this came the need to understand the genomic and functional diversity of non-pathogenic Xanthomonas (NPX) at the species and strain level. This study reports isolation and investigation into the genomic diversity and variation in NPX isolates, chiefly Xanthomonas indica, a newly discovered NPX species from rice. The study establishes the relationship of X. indica strains within clade I of Xanthomonads with another NPX species, X. sontii, also associated with rice seeds. Identification of highly diverse strains, open-pan genome, and systematic hyper-variation at the lipopolysaccharide biosynthetic locus when compared to pathogenic Xanthomonas indicates the acquisition of new functions for adaptation. Furthermore, comparative genomics studies established the absence of major virulence genes such as type III secretion system and effectors, which are present in the pathogens, and the presence of a known bacterial-killing type IV secretion system (X-T4SS). The diverse non-pathogenic strains of X. indica and X. sontii were found to protect rice from bacterial leaf blight pathogen, X. oryzae pv. oryzae (Xoo). The absence of phenotype of an X-T4SS mutant suggests redundancy in the genetic basis of the mechanisms involved in the bioprotection function, which may include multiple genetic loci, such as putative bacteriocinencoding gene clusters and involvement of other factors such as nutrient and niche competition apart from induction of innate immunity through shared microbial-associated molecular patterns. The rice-NPX community and its pathogenic counterpart can be a promising model for understanding plant-microbe-microbiome interaction studies. [ABSTRACT FROM AUTHOR]

Exoribonuclease R (RNase R) is a 3′ hydrolytic exoribonuclease that can degrade structured RNA. Mutation in RNase R affects virulence of certain human pathogenic bacteria. The aim of this study was to determine whether RNase R is necessary for virulence of the phytopathogen that causes bacterial blight in rice, Xanthomonas oryzae pv. oryzae (Xoo). In silico analysis has indicated that RNase R is highly conserved among various xanthomonads. Amino acid sequence alignment of Xoo RNase R with RNase R from various taxa indicated that Xoo RNase R clustered with RNase R of order Xanthomonadales. To study its role in virulence, we generated a gene disruption mutant of Xoo RNase R. The Xoo rnr– mutant is moderately virulence deficient, and the complementing strain (rnr–/pHM1::rnr) rescued the virulence deficiency of the mutant. We investigated swimming and swarming motilities in both nutrient-deficient minimal media and nutrient-optimal media. We observed that RNase R mutation has adversely affected the swimming and swarming motilities of Xoo in optimal media. However, in nutrient-deficient media only swimming motility was noticeably affected. Growth curves in optimal media at suboptimal temperature (15°C cold stress) indicate that the Xoo rnr– mutant grows more slowly than the Xoo wild type and complementing strain (rnr–/pHM1::rnr). Given these findings, we report for the first time that RNase R function is necessary for complete virulence of Xoo in rice. It is also important for motility of Xoo in media and for growth of Xoo at suboptimal temperature. [ABSTRACT FROM AUTHOR]

Pathogen secreted cell-wall-degrading enzymes (CWDEs) induce plant innate immune responses. The expression of rice transcription factor APETALA2/ethylene response factor-152 (OsAP2/ERF152) is enhanced in leaves upon treatment with different CWDEs and upon wounding. Ectopic expression of OsAP2/ERF152 in Arabidopsis leads to induction of immune responses such as callose deposition and upregulation of both salicylic acid- and jasmonic acid/ethyleneresponsive defense genes. Arabidopsis transgenics expressing OsAP2/ ERF152 exhibited resistance to infections caused by both bacterial and fungal pathogens (Pseudomonas syringae pv. tomato DC3000 and Rhizoctonia solani AG1-IA, respectively). Ectopic expression of OsAP2/ ERF152 results in transient activation of mitogen-activated protein kinases 3/6 (MPK3/6), which could be leading to the induction of a broad range immunity in Arabidopsis. [ABSTRACT FROM AUTHOR]

A sub-group of LuxR family of proteins that plays important roles in quorum sensing, a process of cell-cell communication, is widespread in proteobacteria. These proteins have a typical modular structure consisting of N-ter autoinducer binding and C-ter helix-turn-helix (HTH) DNA binding domains. The autoinducer binding domain recognizes signaling molecules which are most often N-acyl homoserine lactones (AHLs) but could also be other novel and yet unidentified molecules. In this study we carried out a series of specific domain swapping and promoter activation experiments as a first step to engineer synthetic signaling modules, taking advantage of the modularity and the versatile/diverse signal specificities of LuxR proteins. In our experiments the N-ter domains from different LuxR homologs were either interchanged or placed in tandem followed by a C-ter domain. The rational design of the hybrid proteins was supported by a structure-based homology modeling studies of three members of the LuxR family (i.e., LasR, RhlR, and OryR being chosen for their unique ligand binding specificities) and of selected chimeras. Our results reveal that these LuxR homologs were able to activate promoter elements that were not their usual targets; we also show that hybrid LuxR proteins retained the ability to recognize the signal specific for their N- ter autoinducer binding domain. However, the activity of hybrid LuxR proteins containing two AHL binding domains in tandem appears to depend on the organization and nature of the introduced domains. This study represents advances in the understanding of the modularity of LuxR proteins and provides additional possibilities to use hybrid proteins in both basic and applied synthetic biology based research.