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1.
    
PIRIN (PRN) is a member of the functionally diverse cupin protein superfamily. There are four members of the Arabidopsis thaliana PRN family, but the roles of these proteins are largely unknown. Here we describe a function of the Arabidopsis PIRIN2 (PRN2) that is related to susceptibility to the bacterial plant pathogen Ralstonia solanacearum. Two prn2 mutant alleles displayed decreased disease development and bacterial growth in response to R.  solanacearum infection. We elucidated the underlying molecular mechanism by analyzing PRN2 interactions with the papain‐like cysteine proteases (PLCPs) XCP2, RD21A, and RD21B, all of which bound to PRN2 in yeast two‐hybrid assays and in Arabidopsis protoplast co‐immunoprecipitation assays. We show that XCP2 is stabilized by PRN2 through inhibition of its autolysis on the basis of PLCP activity profiling assays and enzymatic assays with recombinant protein. The stabilization of XCP2 by PRN2 was also confirmed in planta. Like prn2 mutants, an xcp2 single knockout mutant and xcp2 prn2 double knockout mutant displayed decreased susceptibility to R. solanacearum, suggesting that stabilization of XCP2 by PRN2 underlies susceptibility to R. solanacearum in Arabidopsis.  相似文献   

2.
    
Auxin is a key plant growth regulator that also impacts plant–pathogen interactions. Several lines of evidence suggest that the bacterial plant pathogen Pseudomonas syringae manipulates auxin physiology in Arabidopsis thaliana to promote pathogenesis. Pseudomonas syringae strategies to alter host auxin biology include synthesis of the auxin indole‐3‐acetic acid (IAA) and production of virulence factors that alter auxin responses in host cells. The application of exogenous auxin enhances disease caused by P. syringae strain DC3000. This is hypothesized to result from antagonism between auxin and salicylic acid (SA), a major regulator of plant defenses, but this hypothesis has not been tested in the context of infected plants. We further investigated the role of auxin during pathogenesis by examining the interaction of auxin and SA in the context of infection in plants with elevated endogenous levels of auxin. We demonstrated that elevated IAA biosynthesis in transgenic plants overexpressing the YUCCA 1 (YUC1) auxin biosynthesis gene led to enhanced susceptibility to DC3000. Elevated IAA levels did not interfere significantly with host defenses, as effector‐triggered immunity was active in YUC1‐overexpressing plants, and we observed only minor effects on SA levels and SA‐mediated responses. Furthermore, a plant line carrying both the YUC1‐overexpression transgene and the salicylic acid induction deficient 2 (sid2) mutation, which impairs SA synthesis, exhibited additive effects of enhanced susceptibility from both elevated auxin levels and impaired SA‐mediated defenses. Thus, in IAA overproducing plants, the promotion of pathogen growth occurs independently of suppression of SA‐mediated defenses.  相似文献   

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4.
    
The glucosinolate breakdown product indole‐3‐carbinol functions in cruciferous vegetables as a protective agent against foraging insects. While the toxic and deterrent effects of glucosinolate breakdown on herbivores and pathogens have been studied extensively, the secondary responses that are induced in the plant by indole‐3‐carbinol remain relatively uninvestigated. Here we examined the hypothesis that indole‐3‐carbinol plays a role in influencing plant growth and development by manipulating auxin signaling. We show that indole‐3‐carbinol rapidly and reversibly inhibits root elongation in a dose‐dependent manner, and that this inhibition is accompanied by a loss of auxin activity in the root meristem. A direct interaction between indole‐3‐carbinol and the auxin perception machinery was suggested, as application of indole‐3‐carbinol rescues auxin‐induced root phenotypes. In vitro and yeast‐based protein interaction studies showed that indole‐3‐carbinol perturbs the auxin‐dependent interaction of Transport Inhibitor Response (TIR1) with auxin/3‐indoleacetic acid (Aux/IAAs) proteins, further supporting the possibility that indole‐3‐carbinol acts as an auxin antagonist. The results indicate that chemicals whose production is induced by herbivory, such as indole‐3‐carbinol, function not only to repel herbivores, but also as signaling molecules that directly compete with auxin to fine tune plant growth and development.  相似文献   

5.
    
Bacterial wilt, caused by Ralstonia solanacearum species complex is a key yield‐limiting factor on crops in Guangdong province, China. The genetic diversity of 110 R. solanacearum strains collected from 16 host plants in different areas of Guangdong province was analysed using biovar and phylotype classification schemes. Of 110 strains, fifty‐five strains belong to biovar 3, fifty‐two strains belong to biovar 4, two strains belong to biovar 2 and one strain belonged to biovar 1. Phylotype‐specific multiplex PCR showed that 108 strains belonged to phylotype I (biovars 1, 3, 4) and two strains belonged to phylotype II (biovar 2). The result of phylogenetic relationships analysis based on egl gene sequences demonstrated that 108 strains of phylotype I were grouped into nine previously described sequevars and a new sequevar 57, and two strains of phylotype II were grouped into sequevar 1. Sequevars 15, 34 and 44 widely distributed in Guangdong were predominant sequevars. Sequevar 45 was first reported on potato and pumpkin in China. These results revealed the genetic structure and phylogenetic relationships of R. solanacearum population in Guangdong and will be helpful in bacterial wilt‐resistance breeding.  相似文献   

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7.
    
Plant root secretion can be regarded as signal molecules, which exerts impact on microorganisms in the rhizosphere ecological niche. We obtained gene expression profile of Ralstonia solanacearumPO41 under the root secretions environment of Solanum tuberosum at the time points of 8 hrs, 16 hrs and 24 hrs, respectively, after infection with RNA microarray technology. Bioinformatics tools of differential genes expression analysis, GO functional analysis, cluster analysis and pathway analysis were conducted to find out the pathogenic genes and other related genes. We found that the virulence factors of R. solanacearum mainly focused on the output pathways of toxic protein (Sec pathway, Tat pathway and type III secretion system (T3SS)), the aggregation and transfer of exopolysaccharides and the chemotactic movement and adhesion of flagellum in the potato root secretion ecological niche, while the virulence factors in the atypical output pathway mainly distributed in Sec (secB, secDF, yidc) and Tat (tatA, tatC) pathways to promote the output of folded and unfolded toxic proteins. The fliIATPase was obviously upregulated 8 hrs postinoculation, suggesting that type III secretion system was only active at the early stage of PO41 infection. The upregulated expression of phosphoglucomutase and epimerase showed that the virulence factor of exopolysaccharides (EPS) was synthesized at the early stage of R. solanacearum infection. Chemotactic receptor and motor protein were obviously upregulated within 24 hrs postinoculation. Our study revealed that R. solanacearumPO41 had already colonized to the roots within 24 hrs with the stimulating of root secretion. Some pathogenic genes were upregulated during this period.  相似文献   

8.
    
Bacterial wilt caused by Ralstonia solanacearum is a devastating disease that often threatens potato production and exportation. The potential of four antioxidants (seaweed extract (SWE), yeast, chitosan and ascorbic acid (ASA)) in controlling the disease was evaluated in vitro, under glasshouse and field conditions. The field experiment was conducted in two naturally infested locations: Wardan, Giza (sandy soil), and Talia, Minufiya (silty clay soil). Only chitosan showed antibacterial properties against the pathogen in vitro. SWE, yeast and chitosan showed disease suppression under both glasshouse and field conditions. The disease suppression was accompanied by an increase in the ratio of soil copiotrophic to oligotrophic bacteria. The three antioxidants increased plant nitrogen content, decreased soil OM content and decreased C/N ratio. Disease suppression after chitosan application was clearly observed only in Wardan area, which was characterized by a higher soil alkalinity. A high percentage of antagonistic fluorescent strains similar to Pseudomonas putida group were detected for chitosan‐treated plants in Wardan area (sandy soil). ASA drastically decreased the count of the pathogen in soil, but was conducive to the pathogen in plant tissues. A remarkable increase in microbial (bacterial and fungal) soil and rhizosphere diversity as indicated by PCR‐DGGE analysis for bacterial 16S rRNA and fungal 18S rRNA was recorded. In Talia area (silty clay soil), the soil microbial community was more stable and was in general resistant to the disease where the soils were characterized by high electrical conductivity. SWE, yeast and ASA significantly increased crop production in Talia area only.  相似文献   

9.
    
A field survey was conducted to determine the relationship between Ralstonia solanacearum diversity and severity of bacterial wilt disease in tomato plants grown in plastic greenhouses. Both vegetative and reproductive stages of the plants were surveyed, and the symptoms were empirically categorized into five scales: 0 (asymptomatic): 1st, 2nd, 3rd and 4th. The bacterial wilt pathogen was isolated from infected plants at each disease scale; pathogenic characteristics and population densities of the bacterial strains were assessed. Two hundred and eighty‐two isolates were identified as R. solanacearum, which were divided into three pathogenic types, virulent, avirulent and interim, using the attenuation index (AI) method and a plant inoculation bioassay. Ralstonia solanacearum was detected in all asymptomatic and symptomatic tomato plants, with population numbers, ranging from 10.5 to 86.7 × 105 cfu/g. However, asymptomatic plants harboured only avirulent or interim R. solanacearum, whereas tomato plants displaying 1st or 2nd disease degree contained interim and virulent strains. Additionally, 3rd and 4th degree plants harboured only virulent strains. The disease was more severe in vegetative‐stage plants (disease severity index (DSI) 0.20) with higher total numbers of interim and virulent R. solanacearum strains than those in reproductive‐stage plants (DSI 0.12). Three pathotypes of R. solanacearum coexisted in a competitive growth system in the tomato field, and their distribution closely correlated with the severity of tomato bacterial wilt.  相似文献   

10.
    
The plant hormone auxin is believed to influence almost every aspect of plant growth and development. Auxin transport, biosynthesis and degradation combine to form gradients of the hormone that influence a range of key developmental and environmental response processes. There is abundant genetic evidence for the existence of multiple pathways for auxin biosynthesis and degradation. The complexity of these pathways makes it difficult to obtain a clear picture of the relative importance of specific metabolic pathways during development. We have developed a sensitive mass spectrometry‐based method to simultaneously profile the majority of known auxin precursors and conjugates/catabolites in small amounts of Arabidopsis tissue. The method includes a new derivatization technique for quantification of the most labile of the auxin precursors. We validated the method by profiling the auxin metabolome in root and shoot tissues from various Arabidopsis thaliana ecotypes and auxin over‐producing mutant lines. Substantial differences were shown in metabolite patterns between the lines and tissues. We also found differences of several orders of magnitude in the abundance of auxin metabolites, potentially indicating the relative importance of these compounds in the maintenance of auxin levels and activity. The method that we have established will enable researchers to obtain a better understanding of the dynamics of auxin metabolism and activity during plant growth and development.  相似文献   

11.
Root galls of Brassicaceae caused by Plasmodiophora brassicae are dependent on increased auxin and cytokinin formation. In this study we investigated whether indole glucosinolates are involved in indole‐3‐acetic acid (IAA) biosynthesis in root galls, by using a genetic approach. The cytochrome P450 enzymes, CYP79B2 and CYP79B3, convert tryptophan to indole‐3‐acetaldoxime (IAOx), which is a precursor for indole glucosinolates and the phytoalexin camalexin in Arabidopsis thaliana. Root galls of the Arabidopsis ecotypes Wassilewskija (WS) and Columbia (Col) accumulated camalexin, WS at levels up to 320 μg/g dry weight. By contrast, camalexin was absent in root galls of cyp79b2/b3 double mutants. Infection rate and disease index as a measure of club development in mutant and wild‐type plants of the two ecotypes were investigated and no differences were found in gall formation. This demonstrates that camalexin is an ineffective inhibitor of P. brassicae and indole glucosinolates are not the source of elevated levels of IAA in galls, because free IAA levels in mutant galls were comparable with those in wild type.  相似文献   

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15.
    
A species‐specific Polymerase Chain Reaction (sPCR) method was developed to identify and detect isolates of Ralstonia solanacearum, the cause of bacterial wilt disease in chilli. PCR primers for R. solanacearum were identified by alignment of hrpB gene sequences and selection of sequences specific for R. solanacearum at their 3′ ends. The primers were shown to be specific for R. solanacearum, as no PCR product was obtained when genomic DNA from other bacterial species including closely related Ralstonia species, were used as test species. Lone pair of primers (RshrpBF and RshrpBR) was designed using hrpB gene sequence, unique to R. solanacearum which amplified a predicted PCR product of 810 bp from 20 different isolates. Phylogenetic analysis was also attempted to understand the evolutionary divergence of Indian R. solanacearum isolates. Based on phylogenetic analysis, Indian isolates showed homology with the standard reference isolates from other countries but, interestingly, one new isolate showed complete evolutionary divergence by forming an out‐group.  相似文献   

16.
    
Ralstonia solanacearum is responsible for bacterial wilt affecting many crops worldwide. The emergent population of R. solanacearum (phylotype IIB/4NPB) wilts previously resistant varieties and has rapidly spread throughout Martinique. No conventional method is known to control it. In this study, previous crops used as sanitizing crops were investigated as an environmentally safe alternative method of control. The ability of the emergent population of R. solanacearum to persist in planta and in the rhizosphere of Brassicaceae, Asteraceae and Fabaceae grown as previous crops was evaluated in controlled conditions, and the incidence of bacterial wilt was assessed in the following tomato crop. Results showed that all species carried R. solanacearum latently. Among Brassicaceae and Asteraceae, the highest density of R. solanacearum was found in planta and in the rhizosphere of Tagetes erecta. The density of the R. solanacearum population in the rhizosphere of Raphanus sativus cv. Karacter was significantly higher than that in Raphanus sativus cv. Melody. In Fabaceae, the density of R. solanacearum population in planta was statistically similar in all species. The density of the R. solanacearum population in the rhizosphere of Crotalaria juncea was significantly higher than that in Crotalaria spectabilis. This study showed for the first time that Crotalaria spectabilis and Raphanus sativus cv. Melody grown as previous crops improve the performance of the following tomato with similar effects on R. solanacearum populations in the soil as bare soil. The incidence of the disease in tomato decreased by 86% and 60%, after R. sativus cv. Melody and C. spectabilis, respectively, and the proportion of infected plants also decreased. These results suggest that C. spectabilis and R. sativus cv. Melody can be used as previous crops to help bacterial wilt control in ecological management strategies without drastic suppression of R. solanacearum population in stem tissues and in the rhizosphere.  相似文献   

17.
    
Indole‐3–acetic acid (IAA), an auxin plant hormone, is biosynthesized from tryptophan. The indole‐3–pyruvic acid (IPyA) pathway, involving the tryptophan aminotransferase TAA1 and YUCCA (YUC) enzymes, was recently found to be a major IAA biosynthetic pathway in Arabidopsis. TAA1 catalyzes the conversion of tryptophan to IPyA, and YUC produces IAA from IPyA. Using a chemical biology approach with maize coleoptiles, we identified 5–(4–chlorophenyl)‐4H‐1,2,4–triazole‐3–thiol (yucasin) as a potent inhibitor of IAA biosynthesis in YUC‐expressing coleoptile tips. Enzymatic analysis of recombinant AtYUC1‐His suggested that yucasin strongly inhibited YUC1‐His activity against the substrate IPyA in a competitive manner. Phenotypic analysis of Arabidopsis YUC1 over‐expression lines (35S::YUC1) demonstrated that yucasin acts in IAA biosynthesis catalyzed by YUC. In addition, 35S::YUC1 seedlings showed resistance to yucasin in terms of root growth. A loss‐of‐function mutant of TAA1, sav3–2, was hypersensitive to yucasin in terms of root growth and hypocotyl elongation of etiolated seedlings. Yucasin combined with the TAA1 inhibitor l –kynurenine acted additively in Arabidopsis seedlings, producing a phenotype similar to yucasin‐treated sav3–2 seedlings, indicating the importance of IAA biosynthesis via the IPyA pathway in root growth and leaf vascular development. The present study showed that yucasin is a potent inhibitor of YUC enzymes that offers an effective tool for analyzing the contribution of IAA biosynthesis via the IPyA pathway to plant development and physiological processes.  相似文献   

18.
    
Plants are highly capable of recognizing and defending themselves against invading microbes. Adapted plant pathogens secrete effector molecules to suppress the host's immune system. These molecules may be recognized by host‐encoded resistance proteins, which then trigger defense in the form of the hypersensitive response (HR) leading to programmed cell death of the host tissue at the infection site. The three proteins PEN1, PEN2 and PEN3 have been found to act as central components in cell wall‐based defense against the non‐adapted powdery mildew Blumeria graminis fsp. hordei (Bgh). We found that loss of function mutations in any of the three PEN genes cause decreased hypersensitive cell death triggered by recognition of effectors from oomycete and bacterial pathogens in Arabidopsis. There were considerable additive effects of the mutations. The HR induced by recognition of AvrRpm1 was almost completely abolished in the pen2 pen3 and pen1 pen3 double mutants and the loss of cell death could be linked to indole glucosinolate breakdown products. However, the loss of the HR in pen double mutants did not affect the plants' ability to restrict bacterial growth, whereas resistance to avirulent isolates of the oomycete Hyaloperonospora arabidopsidis was strongly compromised. In contrast, the double and triple mutants demonstrated varying degrees of run‐away cell death in response to Bgh. Taken together, our results indicate that the three genes PEN1, PEN2 and PEN3 extend in functionality beyond their previously recognized functions in cell wall‐based defense against non‐host pathogens.  相似文献   

19.
  总被引：2，自引：0，他引：2  
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20.
    
Auxin is a fundamental plant hormone and its localization within organs plays pivotal roles in plant growth and development. Analysis of many Arabidopsis mutants that were defective in auxin biosynthesis revealed that the indole‐3‐pyruvic acid (IPA) pathway, catalyzed by the TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS (TAA) and YUCCA (YUC) families, is the major biosynthetic pathway of indole‐3‐acetic acid (IAA). In contrast, little information is known about the molecular mechanisms of auxin biosynthesis in rice. In this study, we identified a auxin‐related rice mutant, fish bone (fib). FIB encodes an orthologue of TAA genes and loss of FIB function resulted in pleiotropic abnormal phenotypes, such as small leaves with large lamina joint angles, abnormal vascular development, small panicles, abnormal organ identity and defects in root development, together with a reduction in internal IAA levels. Moreover, we found that auxin sensitivity and polar transport activity were altered in the fib mutant. From these results, we suggest that FIB plays a pivotal role in IAA biosynthesis in rice and that auxin biosynthesis, transport and sensitivity are closely interrelated.  相似文献   

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