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Novel Disease Susceptibility Factors for Fungal Necrotrophic Pathogens in Arabidopsis  [PDF]
Albor Dobón?,Juan Vicente Canet?,Javier García-Andrade?,Carlos Angulo?,Lutz Neumetzler?,Staffan Persson?,Pablo Vera
PLOS Pathogens , 2015, DOI: 10.1371/journal.ppat.1004800
Abstract: Host cells use an intricate signaling system to respond to invasions by pathogenic microorganisms. Although several signaling components of disease resistance against necrotrophic fungal pathogens have been identified, our understanding for how molecular components and host processes contribute to plant disease susceptibility is rather sparse. Here, we identified four transcription factors (TFs) from Arabidopsis that limit pathogen spread. Arabidopsis mutants defective in any of these TFs displayed increased disease susceptibility to Botrytis cinerea and Plectosphaerella cucumerina, and a general activation of non-immune host processes that contribute to plant disease susceptibility. Transcriptome analyses revealed that the mutants share a common transcriptional signature of 77 up-regulated genes. We characterized several of the up-regulated genes that encode peptides with a secretion signal, which we named PROVIR (for provirulence) factors. Forward and reverse genetic analyses revealed that many of the PROVIRs are important for disease susceptibility of the host to fungal necrotrophs. The TFs and PROVIRs identified in our work thus represent novel genetic determinants for plant disease susceptibility to necrotrophic fungal pathogens.
The roles of aldehyde dehydrogenases (ALDHs) in the PDH bypass of Arabidopsis
Yanling Wei, Ming Lin, David J Oliver, Patrick S Schnable
BMC Biochemistry , 2009, DOI: 10.1186/1471-2091-10-7
Abstract: To test for the presence of the PDH bypass in the sporophytic tissue of plants, Arabidopsis plants homozygous for mutant alleles of all three Family 2 ALDH genes were fed with 14C-ethanol along with wild type controls. Comparisons of the incorporation rates of 14C-ethanol into fatty acids in mutants and wild type controls provided direct evidence for the presence of the PDH bypass in sporophytic tissue. Among the three Family 2 ALDHs, one of the two mitochondrial ALDHs (ALDH2B4) appears to be the primary contributor to this pathway. Surprisingly, single, double and triple ALDH mutants of Arabidopsis did not exhibit detectable phenotypes, even though a Family 2 ALDH gene is required for normal anther development in maize.The PDH bypass is active in sporophytic tissue of plants. Blocking this pathway via triple ALDH mutants does not uncover obvious visible phenotypes.Aldehydes vary in length and in characteristics of their alkyl chains but all are usually deleterious to biological systems due to their chemical reactivity. Aldehyde dehydrogenases (ALDHs, EC 1.2.1) oxidize aldehydes into carboxylic acids, using NAD+ or NADP+ as a co-factor. As such ALDHs play an important role in detoxifying aldehydes that are generated endogenously or introduced from the environment. ALDHs are very diverse in that some only use either NAD+ or NADP+ as the co-factor, while others can use both, some oxidize only a limited number of aldehydes, while others have broader substrate spectra, and ALDHs exist in various subcellular compartments, including the cytosol, mitochondria, plastids and microsomes.Over 550 ALDH genes have been identified across virtually all species, and those from eukaryotes have been classified into more than 20 families [1]. Family 2 ALDHs are mitochondrial or cytosolic homotetrameric enzymes. The well studied human mitochondrial Family 2 ALDH, ALDH2, detoxifies acetaldehyde generated via alcohol intake [2]. Family 2 ALDHs in plants have gained attention since the cl
枸杞WRKY3基因克隆及组织表达分析  [PDF]
- , 2016,
Abstract: 以枸杞为材料, 采用PCR及RACE方法,克隆了枸杞WRKY转录因子基因 cDNA序列,命名为Lb WRKY3 ,GenBank登录号为 KX196192。 在生物信息学分析的基础上,进行亚细胞定位、基因表达分析。结果显示:(1)Lb WRKY3 开放阅读框ORF长度为1 068 bp, 编码356个氨基酸。(2)生物信息学分析显示,Lb WRKY3 编码蛋白具有一个WRKY结构域,二级结构中不规则卷曲结构所占比例最大(58.67%),延伸链结构次之(18.88%),α螺旋比例为15.82%,β转角最少,仅为 6.63%; Lb WRKY3蛋白与案头菊WRKY蛋白、黄花蒿WRKY蛋白相似性较高。(3) 亚细胞定位显示,Lb WRKY3 蛋白定位于细胞核。 (4)实时定量PCR分析表明,Lb WRKY3在根中表达量最高,在花中表达量最低; 在枸杞果实发育过程中Lb WRKY3均有表达,表达量随果实成熟逐渐升高,并于35 d达到峰值; Lb WRKY3基因在果实中的表达具有组织特异性表达特性(果肉>果皮>种子)。研究表明,Lb WRKY3 基因参与了枸杞果实生长发育调控。
Arabidopsis Transcriptome Analysis Reveals Key Roles of Melatonin in Plant Defense Systems  [PDF]
Sarah Weeda, Na Zhang, Xiaolei Zhao, Grace Ndip, Yangdong Guo, Gregory A. Buck, Conggui Fu, Shuxin Ren
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0093462
Abstract: Melatonin is a ubiquitous molecule and exists across kingdoms including plant species. Studies on melatonin in plants have mainly focused on its physiological influence on growth and development, and on its biosynthesis. Much less attention has been drawn to its affect on genome-wide gene expression. To comprehensively investigate the role(s) of melatonin at the genomics level, we utilized mRNA-seq technology to analyze Arabidopsis plants subjected to a 16-hour 100 pM (low) and 1 mM (high) melatonin treatment. The expression profiles were analyzed to identify differentially expressed genes. 100 pM melatonin treatment significantly affected the expression of only 81 genes with 51 down-regulated and 30 up-regulated. However, 1 mM melatonin significantly altered 1308 genes with 566 up-regulated and 742 down-regulated. Not all genes altered by low melatonin were affected by high melatonin, indicating different roles of melatonin in regulation of plant growth and development under low and high concentrations. Furthermore, a large number of genes altered by melatonin were involved in plant stress defense. Transcript levels for many stress receptors, kinases, and stress-associated calcium signals were up-regulated. The majority of transcription factors identified were also involved in plant stress defense. Additionally, most identified genes in ABA, ET, SA and JA pathways were up-regulated, while genes pertaining to auxin responses and signaling, peroxidases, and those associated with cell wall synthesis and modifications were mostly down-regulated. Our results indicate critical roles of melatonin in plant defense against various environmental stresses, and provide a framework for functional analysis of genes in melatonin-mediated signaling pathways.
Arabidopsis Heterotrimeric G-Proteins Play a Critical Role in Host and Nonhost Resistance against Pseudomonas syringae Pathogens  [PDF]
Seonghee Lee, Clemencia M. Rojas, Yasuhiro Ishiga, Sona Pandey, Kirankumar S. Mysore
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0082445
Abstract: Heterotrimeric G-proteins have been proposed to be involved in many aspects of plant disease resistance but their precise role in mediating nonhost disease resistance is not well understood. We evaluated the roles of specific subunits of heterotrimeric G-proteins using knock-out mutants of Arabidopsis Gα, Gβ and Gγ subunits in response to host and nonhost Pseudomonas pathogens. Plants lacking functional Gα, Gβ and Gγ1Gγ2 proteins displayed enhanced bacterial growth and disease susceptibility in response to host and nonhost pathogens. Mutations of single Gγ subunits Gγ1, Gγ2 and Gγ3 did not alter bacterial disease resistance. Some specificity of subunit usage was observed when comparing host pathogen versus nonhost pathogen. Overexpression of both Gα and Gβ led to reduced bacterial multiplication of nonhost pathogen P. syringae pv. tabaci whereas overexpression of Gβ, but not of Gα, resulted in reduced bacterial growth of host pathogen P. syringae pv. maculicola, compared to wild-type Col-0. Moreover, the regulation of stomatal aperture by bacterial pathogens was altered in Gα and Gβ mutants but not in any of the single or double Gγ mutants. Taken together, these data substantiate the critical role of heterotrimeric G-proteins in plant innate immunity and stomatal modulation in response to P. syringae.
Roles of arabidopsis WRKY18, WRKY40 and WRKY60 transcription factors in plant responses to abscisic acid and abiotic stress
Han Chen, Zhibing Lai, Junwei Shi, Yong Xiao, Zhixiang Chen, Xinping Xu
BMC Plant Biology , 2010, DOI: 10.1186/1471-2229-10-281
Abstract: We report that the three WRKYs are involved in plant responses to abscisic acid (ABA) and abiotic stress. Through analysis of single, double, and triple mutants and overexpression lines for the WRKY genes, we have shown that WRKY18 and WRKY60 have a positive effect on plant ABA sensitivity for inhibition of seed germination and root growth. The same two WRKY genes also enhance plant sensitivity to salt and osmotic stress. WRKY40, on the other hand, antagonizes WRKY18 and WRKY60 in the effect on plant sensitivity to ABA and abiotic stress in germination and growth assays. Both WRKY18 and WRKY40 are rapidly induced by ABA, while induction of WRKY60 by ABA is delayed. ABA-inducible expression of WRKY60 is almost completely abolished in the wrky18 and wrky40 mutants. WRKY18 and WRKY40 recognize a cluster of W-box sequences in the WRKY60 promoter and activate WRKY60 expression in protoplasts. Thus, WRKY60 might be a direct target gene of WRKY18 and WRKY40 in ABA signaling. Using a stable transgenic reporter/effector system, we have shown that both WRKY18 and WRKY60 act as weak transcriptional activators while WRKY40 is a transcriptional repressor in plant cells.We propose that the three related WRKY transcription factors form a highly interacting regulatory network that modulates gene expression in both plant defense and stress responses by acting as either transcription activator or repressor.Plants are constantly exposed to a variety of biotic and abiotic stresses and have evolved intricate mechanisms to sense and respond to the adverse conditions. Phytohormones such as salicylic acid (SA), ethylene (ET), jasmonic acid (JA) and abscisic acid (ABA) play important roles in the regulation of plant responses to the adverse environmental conditions. In Arabidopsis, mutants deficient in SA biosynthesis (e.g. sid2) or signalling (e.g. npr1) exhibit enhanced susceptibility to biotrophic pathogens, which parasitize on plant living tissue [1,2]. ET- and JA-mediated signaling pat
Arabidopsis Serine Decarboxylase Mutants Implicate the Roles of Ethanolamine in Plant Growth and Development  [PDF]
Yerim Kwon,Si-in Yu,Hyoungseok Lee,Joung Han Yim,Jian-Kang Zhu,Byeong-ha Lee
International Journal of Molecular Sciences , 2012, DOI: 10.3390/ijms13033176
Abstract: Ethanolamine is important for synthesis of choline, phosphatidylethanolamine (PE) and phosphatidylcholine (PC) in plants. The latter two phospholipids are the major phospholipids in eukaryotic membranes. In plants, ethanolamine is mainly synthesized directly from serine by serine decarboxylase. Serine decarboxylase is unique to plants and was previously shown to have highly specific activity to L-serine. While serine decarboxylase was biochemically characterized, its functions and importance in plants were not biologically elucidated due to the lack of serine decarboxylase mutants. Here we characterized an Arabidopsis mutant defective in serine decarboxylase, named atsdc-1 ( Arabidopsis thaliana serine decarboxylase-1). The atsdc-1 mutants showed necrotic lesions in leaves, multiple inflorescences, sterility in flower, and early flowering in short day conditions. These defects were rescued by ethanolamine application to atsdc-1, suggesting the roles of ethanolamine as well as serine decarboxylase in plant development. In addition, molecular analysis of serine decarboxylase suggests that Arabidopsis serine decarboxylase is cytosol-localized and expressed in all tissue.
核桃WRKY4基因的克隆与表达分析  [PDF]
核农学报 , 2014, DOI: 10.11869/j.issn.100-8551.2014.07.1188
Abstract: WRKY转录调控因子广泛参与植物的生长发育、生物胁迫和非生物胁迫等生理过程。本研究利用reversetranscription-polymerasechainreaction(RT-PCR)及rapidamplificationofcDNAends(RACE)技术克隆了核桃(JuglansregiaL.)WRKY基因cDNA全长序列,命名为WRKY4(GenBank登录号为KC795551.1)。结果表明,克隆到的片段长度为2174bp,完整开放阅读框为1554bp,编码517个氨基酸。序列分析表明WRKY4基因含有2个WRKY保守结构域和2个C2H2锌指结构域,属于WRKY基因家族第Ⅰ类成员。利用实时荧光定量PCR分析4℃低温和自然低温条件对该基因表达的影响以及组织表达模式。结果表明WRKY4受低温诱导表达,能够在低温胁迫的早期响应这一生理过程。WRKY4在树皮(韧皮部)、雌花、花芽和叶片中均有表达,且在树皮中表达量最高,具有组织特异性。研究结果可为核桃抗寒基因工程育种提供基因资源。
ERF5 and ERF6 Play Redundant Roles as Positive Regulators of JA/Et-Mediated Defense against Botrytis cinerea in Arabidopsis  [PDF]
Caroline S. Moffat, Robert A. Ingle, Deepthi L. Wathugala, Nigel J. Saunders, Heather Knight, Marc R. Knight
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0035995
Abstract: The ethylene response factor (ERF) family in Arabidopsis thaliana comprises 122 members in 12 groups, yet the biological functions of the majority remain unknown. Of the group IX ERFs, the IXc subgroup has been studied the most, and includes ERF1, ERF14 and ORA59, which play roles in plant innate immunity. Here we investigate the biological functions of two members of the less studied IXb subgroup: ERF5 and ERF6. In order to identify potential targets of these transcription factors, microarray analyses were performed on plants constitutively expressing either ERF5 or ERF6. Expression of defense genes, JA/Et-responsive genes and genes containing the GCC box promoter motif were significantly upregulated in both ERF5 and ERF6 transgenic plants, suggesting that ERF5 and ERF6 may act as positive regulators of JA-mediated defense and potentially overlap in their function. Since defense against necrotrophic pathogens is generally mediated through JA/Et-signalling, resistance against the fungal necrotroph Botrytis cinerea was examined. Constitutive expression of ERF5 or ERF6 resulted in significantly increased resistance. Although no significant difference in susceptibility to B. cinerea was observed in either erf5 or erf6 mutants, the erf5 erf6 double mutant showed a significant increase in susceptibility, which was likely due to compromised JA-mediated gene expression, since JA-induced gene expression was reduced in the double mutant. Taken together these data suggest that ERF5 and ERF6 play positive but redundant roles in defense against B. cinerea. Since mutual antagonism between JA/Et and salicylic acid (SA) signalling is well known, the UV-C inducibility of an SA-inducible gene, PR-1, was examined. Reduced inducibilty in both ERF5 and ERF6 constitutive overexepressors was consistent with suppression of SA-mediated signalling, as was an increased susceptibility to avirulent Pseudomonas syringae. These data suggest that ERF5 and ERF6 may also play a role in the antagonistic crosstalk between the JA/Et and SA signalling pathways.
Regulatory Roles of Cytokinins and Cytokinin Signaling in Response to Potassium Deficiency in Arabidopsis  [PDF]
Youn-Jeong Nam, Lam-Son Phan Tran, Mikiko Kojima, Hitoshi Sakakibara, Rie Nishiyama, Ryoung Shin
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0047797
Abstract: Potassium (K) is an important plant macronutrient that has various functions throughout the whole plant over its entire life span. Cytokinins (CKs) are known to regulate macronutrient homeostasis by controlling the expression of nitrate, phosphate and sulfate transporters. Although several studies have described how CKs signal deficiencies for some macronutrients, the roles of CKs in K signaling are poorly understood. CK content has been shown to decrease under K-starved conditions. Specifically, a CK-deficient mutant was more tolerant to low K than wild-type; however, a plant with an overaccumulation of CKs was more sensitive to low K. These results suggest that K deprivation alters CK metabolism, leading to a decrease in CK content. To investigate this phenomenon further, several Arabidopsis lines, including a CK-deficient mutant and CK receptor mutants, were analyzed in low K conditions using molecular, genetic and biochemical approaches. ROS accumulation and root hair growth in low K were also influenced by CKs. CK receptor mutants lost the responsiveness to K-deficient signaling, including ROS accumulation and root hair growth, but the CK-deficient mutant accumulated more ROS and exhibited up-regulated expression of HAK5, which is a high-affinity K uptake transporter gene that is rapidly induced by low K stress in ROS- and ethylene-dependent manner in response to low K. From these results, we conclude that a reduction in CK levels subsequently allows fast and effective stimulation of low K-induced ROS accumulation, root hair growth and HAK5 expression, leading to plant adaptation to low K conditions.
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