Fusaristatin A production negatively affects the growth and aggressiveness of the wheat pathogen Fusarium pseudograminearum.

Fusarium pseudograminearum (Fp), the causative fungal pathogen of the diseases Fusarium crown rot, is an important constraint to cereals production in many countries including Australia. Fp produces a number of secondary metabolites throughout its life cycle. One of these metabolites, the cyclic lipopeptide fusaristatin A, is encoded by a specific gene cluster containing a polyketide synthase and a three-module non-ribosomal peptide synthetase. However, a recent survey of Fp populations across Australia suggests that this cluster may only be present in a subset of isolates from Western Australia (WA). In this study, we screened 319 Fp isolates from WA and 110 Fp isolates from the Australian eastern states of New South Wales, Victoria, Queensland and South Australia to examine the distribution of this gene cluster among Australian Fp populations. The fusaristatin A gene cluster was found to be present in ~50% of Fp isolates from WA but completely absent in Fp isolates from eastern states. To determine its potential function, mutants of the fusaristatin A gene cluster were generated by disrupting the non-ribosomal peptide synthetase and polyketide synthase genes simultaneously in two different parental backgrounds. The mutants showed increased growth rates and were significantly more aggressive than their respective parental strains on wheat in crown rot pathogenicity assays. This suggested that fusaristatin A has a negative effect on fungal development and aggressiveness. The possible reasons for the geographically restricted presence of the fusaristatin A gene cluster and its role in fungal biology are discussed.

The tomato I gene for Fusarium wilt resistance encodes an atypical leucine-rich repeat receptor-like protein whose function is nevertheless dependent on SOBIR1 and SERK3/BAK1.

We have identified the tomato I gene for resistance to the Fusarium wilt fungus Fusarium oxysporum f. sp. lycopersici (Fol) and show that it encodes a membrane-anchored leucine-rich repeat receptor-like protein (LRR-RLP). Unlike most other LRR-RLP genes involved in plant defence, the I gene is not a member of a gene cluster and contains introns in its coding sequence. The I gene encodes a loopout domain larger than those in most other LRR-RLPs, with a distinct composition rich in serine and threonine residues. The I protein also lacks a basic cytosolic domain. Instead, this domain is rich in aromatic residues that could form a second transmembrane domain. The I protein recognises the Fol Avr1 effector protein, but, unlike many other LRR-RLPs, recognition specificity is determined in the C-terminal half of the protein by polymorphic amino acid residues in the LRRs just preceding the loopout domain and in the loopout domain itself. Despite these differences, we show that I/Avr1-dependent necrosis in Nicotiana benthamiana depends on the LRR receptor-like kinases (RLKs) SERK3/BAK1 and SOBIR1. Sequence comparisons revealed that the I protein and other LRR-RLPs involved in plant defence all carry residues in their last LRR and C-terminal LRR capping domain that are conserved with SERK3/BAK1-interacting residues in the same relative positions in the LRR-RLKs BRI1 and PSKR1. Tyrosine mutations of two of these conserved residues, Q922 and T925, abolished I/Avr1-dependent necrosis in N. benthamiana, consistent with similar mutations in BRI1 and PSKR1 preventing their interaction with SERK3/BAK1.

Salicylic Acid-Dependent Plant Stress Signaling via Mitochondrial Succinate Dehydrogenase.

Mitochondria are known for their role in ATP production and generation of reactive oxygen species, but little is known about the mechanism of their early involvement in plant stress signaling. The role of mitochondrial succinate dehydrogenase (SDH) in salicylic acid (SA) signaling was analyzed using two mutants: disrupted in stress response1 (dsr1), which is a point mutation in SDH1 identified in a loss of SA signaling screen, and a knockdown mutant (sdhaf2) for SDH assembly factor 2 that is required for FAD insertion into SDH1. Both mutants showed strongly decreased SA-inducible stress promoter responses and low SDH maximum capacity compared to wild type, while dsr1 also showed low succinate affinity, low catalytic efficiency, and increased resistance to SDH competitive inhibitors. The SA-induced promoter responses could be partially rescued in sdhaf2, but not in dsr1, by supplementing the plant growth media with succinate. Kinetic characterization showed that low concentrations of either SA or ubiquinone binding site inhibitors increased SDH activity and induced mitochondrial H2O2 production. Both dsr1 and sdhaf2 showed lower rates of SA-dependent H2O2 production in vitro in line with their low SA-dependent stress signaling responses in vivo. This provides quantitative and kinetic evidence that SA acts at or near the ubiquinone binding site of SDH to stimulate activity and contributes to plant stress signaling by increased rates of mitochondrial H2O2 production, leading to part of the SA-dependent transcriptional response in plant cells.

Transcriptome analysis of the fungal pathogen Fusarium oxysporum f. sp. medicaginis during colonisation of resistant and susceptible Medicago truncatula hosts identifies differential pathogenicity profiles and novel candidate effectors.

BACKGROUND: Pathogenic members of the Fusarium oxysporum species complex are responsible for vascular wilt disease on many important crops including legumes, where they can be one of the most destructive disease causing necrotrophic fungi. We previously developed a model legume-infecting pathosystem based on the reference legume Medicago truncatula and a pathogenic F. oxysporum forma specialis (f. sp.) medicaginis (Fom). To dissect the molecular pathogenicity arsenal used by this root-infecting pathogen, we sequenced its transcriptome during infection of a susceptible and resistant host accession. RESULTS: High coverage RNA-Seq of Fom infected root samples harvested from susceptible (DZA315) or resistant (A17) M. truncatula seedlings at early or later stages of infection (2 or 7 days post infection (dpi)) and from vegetative (in vitro) samples facilitated the identification of unique and overlapping sets of in planta differentially expressed genes. This included enrichment, particularly in DZA315 in planta up-regulated datasets, for proteins associated with sugar, protein and plant cell wall metabolism, membrane transport, nutrient uptake and oxidative processes. Genes encoding effector-like proteins were identified, including homologues of the F. oxysporum f. sp. lycopersici Secreted In Xylem (SIX) proteins, and several novel candidate effectors based on predicted secretion, small protein size and high in-planta induced expression. The majority of the effector candidates contain no known protein domains but do share high similarity to predicted proteins predominantly from other F. oxysporum ff. spp. as well as other Fusaria (F. solani, F. fujikori, F. verticilloides, F. graminearum and F. pseudograminearum), and from another wilt pathogen of the same class, a Verticillium species. Overall, this suggests these novel effector candidates may play important roles in Fusaria and wilt pathogen virulence. CONCLUSION: Combining high coverage in planta RNA-Seq with knowledge of fungal pathogenicity protein features facilitated the identification of differentially expressed pathogenicity associated genes and novel effector candidates expressed during infection of a resistant or susceptible M. truncatula host. The knowledge from this first in depth in planta transcriptome sequencing of any F. oxysporum ff. spp. pathogenic on legumes will facilitate the dissection of Fusarium wilt pathogenicity mechanisms on many important legume crops.

Comparative genomics and prediction of conditionally dispensable sequences in legume-infecting Fusarium oxysporum formae speciales facilitates identification of candidate effectors.

BACKGROUND: Soil-borne fungi of the Fusarium oxysporum species complex cause devastating wilt disease on many crops including legumes that supply human dietary protein needs across many parts of the globe. We present and compare draft genome assemblies for three legume-infecting formae speciales (ff. spp.): F. oxysporum f. sp. ciceris (Foc-38-1) and f. sp. pisi (Fop-37622), significant pathogens of chickpea and pea respectively, the world's second and third most important grain legumes, and lastly f. sp. medicaginis (Fom-5190a) for which we developed a model legume pathosystem utilising Medicago truncatula. RESULTS: Focusing on the identification of pathogenicity gene content, we leveraged the reference genomes of Fusarium pathogens F. oxysporum f. sp. lycopersici (tomato-infecting) and F. solani (pea-infecting) and their well-characterised core and dispensable chromosomes to predict genomic organisation in the newly sequenced legume-infecting isolates. Dispensable chromosomes are not essential for growth and in Fusarium species are known to be enriched in host-specificity and pathogenicity-associated genes. Comparative genomics of the publicly available Fusarium species revealed differential patterns of sequence conservation across F. oxysporum formae speciales, with legume-pathogenic formae speciales not exhibiting greater sequence conservation between them relative to non-legume-infecting formae speciales, possibly indicating the lack of a common ancestral source for legume pathogenicity. Combining predicted dispensable gene content with in planta expression in the model legume-infecting isolate, we identified small conserved regions and candidate effectors, four of which shared greatest similarity to proteins from another legume-infecting ff. spp. CONCLUSIONS: We demonstrate that distinction of core and potential dispensable genomic regions of novel F. oxysporum genomes is an effective tool to facilitate effector discovery and the identification of gene content possibly linked to host specificity. While the legume-infecting isolates didn't share large genomic regions of pathogenicity-related content, smaller regions and candidate effector proteins were highly conserved, suggesting that they may play specific roles in inducing disease on legume hosts.

Characterization of a JAZ7 activation-tagged Arabidopsis mutant with increased susceptibility to the fungal pathogen Fusarium oxysporum.

In Arabidopsis, jasmonate (JA)-signaling plays a key role in mediating Fusarium oxysporum disease outcome. However, the roles of JASMONATE ZIM-domain (JAZ) proteins that repress JA-signaling have not been characterized in host resistance or susceptibility to this pathogen. Here, we found most JAZ genes are induced following F. oxysporum challenge, and screening T-DNA insertion lines in Arabidopsis JAZ family members identified a highly disease-susceptible JAZ7 mutant (jaz7-1D). This mutant exhibited constitutive JAZ7 expression and conferred increased JA-sensitivity, suggesting activation of JA-signaling. Unlike jaz7 loss-of-function alleles, jaz7-1D also had enhanced JA-responsive gene expression, altered development and increased susceptibility to the bacterial pathogen PstDC3000 that also disrupts host JA-responses. We also demonstrate that JAZ7 interacts with transcription factors functioning as activators (MYC3, MYC4) or repressors (JAM1) of JA-signaling and contains a functional EAR repressor motif mediating transcriptional repression via the co-repressor TOPLESS (TPL). We propose through direct TPL recruitment, in wild-type plants JAZ7 functions as a repressor within the JA-response network and that in jaz7-1D plants, misregulated ectopic JAZ7 expression hyper-activates JA-signaling in part by disturbing finely-tuned COI1-JAZ-TPL-TF complexes.

Mitochondrial complex II has a key role in mitochondrial-derived reactive oxygen species influence on plant stress gene regulation and defense.

Mitochondria are both a source of ATP and a site of reactive oxygen species (ROS) production. However, there is little information on the sites of mitochondrial ROS (mROS) production or the biological role of such mROS in plants. We provide genetic proof that mitochondrial complex II (Complex II) of the electron transport chain contributes to localized mROS that regulates plant stress and defense responses. We identify an Arabidopsis mutant in the Complex II subunit, SDH1-1, through a screen for mutants lacking GSTF8 gene expression in response to salicylic acid (SA). GSTF8 is an early stress-responsive gene whose transcription is induced by biotic and abiotic stresses, and its expression is commonly used as a marker of early stress and defense responses. Transcriptional analysis of this mutant, disrupted in stress responses 1 (dsr1), showed that it had altered SA-mediated gene expression for specific downstream stress and defense genes, and it exhibited increased susceptibility to specific fungal and bacterial pathogens. The dsr1 mutant also showed significantly reduced succinate dehydrogenase activity. Using in vivo fluorescence assays, we demonstrated that root cell ROS production occurred primarily from mitochondria and was lower in the mutant in response to SA. In addition, leaf ROS production was lower in the mutant after avirulent bacterial infection. This mutation, in a conserved region of SDH1-1, is a unique plant mitochondrial mutant that exhibits phenotypes associated with lowered mROS production. It provides critical insights into Complex II function with implications for understanding Complex II's role in mitochondrial diseases across eukaryotes.

The lateral organ boundaries domain transcription factor LBD20 functions in Fusarium wilt Susceptibility and jasmonate signaling in Arabidopsis.

The LATERAL ORGAN BOUNDARIES (LOB) DOMAIN (LBD) gene family encodes plant-specific transcriptional regulators functioning in organ development. In a screen of Arabidopsis (Arabidopsis thaliana) sequence-indexed transferred DNA insertion mutants, we found disruption of the LOB DOMAIN-CONTAINING PROTEIN20 (LBD20) gene led to increased resistance to the root-infecting vascular wilt pathogen Fusarium oxysporum. In wild-type plants, LBD20 transcripts were barely detectable in leaves but abundant in roots, where they were further induced after F. oxysporum inoculation or methyl jasmonate treatment. Induction of LBD20 expression in roots was abolished in coronatine insensitive1 (coi1) and myc2 (allelic to jasmonate insensitive1) mutants, suggesting LBD20 may function in jasmonate (JA) signaling. Consistent with this, expression of the JA-regulated THIONIN2.1 (Thi2.1) and VEGETATIVE STORAGE PROTEIN2 (VSP2) genes were up-regulated in shoots of lbd20 following treatment of roots with F. oxysporum or methyl jasmonate. However, PLANT DEFENSIN1.2 expression was unaltered, indicating a repressor role for LBD20 in a branch of the JA-signaling pathway. Plants overexpressing LBD20 (LBD20-OX) had reduced Thi2.1 and VSP2 expression. There was a significant correlation between increased LBD20 expression in the LBD20-OX lines with both Thi2.1 and VSP2 repression, and reduced survival following F. oxysporum infection. Chlorosis resulting from application of F. oxysporum culture filtrate was also reduced in lbd20 leaves relative to the wild type. Taken together, LBD20 is a F. oxysporum susceptibility gene that appears to regulate components of JA signaling downstream of COI1 and MYC2 that are required for full elicitation of F. oxysporum- and JA-dependent responses. To our knowledge, this is the first demonstration of a role for a LBD gene family member in either biotic stress or JA signaling.

Streptomyces and their specialised metabolites for phytopathogen control - comparative in vitro and in planta metabolic approaches.

In the search for new crop protection microbial biocontrol agents, isolates from the genus Streptomyces are commonly found with promising attributes. Streptomyces are natural soil dwellers and have evolved as plant symbionts producing specialised metabolites with antibiotic and antifungal activities. Streptomyces biocontrol strains can effectively suppress plant pathogens via direct antimicrobial activity, but also induce plant resistance through indirect biosynthetic pathways. The investigation of factors stimulating the production and release of Streptomyces bioactive compounds is commonly conducted in vitro, between Streptomyces sp. and a plant pathogen. However, recent research is starting to shed light on the behaviour of these biocontrol agents in planta, where the biotic and abiotic conditions share little similarity to those of controlled laboratory conditions. With a focus on specialised metabolites, this review details (i) the various methods by which Streptomyces biocontrol agents employ specialised metabolites as an additional line of defence against plant pathogens, (ii) the signals shared in the tripartite system of plant, pathogen and biocontrol agent, and (iii) an outlook on new approaches to expedite the identification and ecological understanding of these metabolites under a crop protection lens.

A highly conserved effector in Fusarium oxysporum is required for full virulence on Arabidopsis.

Secreted-in-xylem (SIX) proteins of the vascular wilt pathogen Fusarium oxysporum f. sp. lycopersici are secreted during infection of tomato and function in virulence or avirulence. F. oxysporum formae speciales have specific host ranges but the roles of SIX proteins in diverse hosts are unknown. We identified homologs of F. oxysporum f. sp. lycopersici SIX1, SIX4, SIX8, and SIX9 in the genome of Arabidopsis infecting isolate Fo5176. A SIX4 homolog (termed Fo5176-SIX4) differed from that of F. oxysporum f. sp. lycopersici (Fol-SIX4) by only two amino acids, and its expression was induced during infection of Arabidopsis. Transgenic Arabidopsis plants constitutively expressing Fo5176-SIX4 had increased disease symptoms with Fo5176. Conversely, Fo5176-SIX4 gene knock-out mutants (Δsix4) had significantly reduced virulence on Arabidopsis, and this was associated with reduced fungal biomass and host jasmonate-mediated gene expression, the latter known to be essential for host symptom development. Full virulence was restored by complementation of Δsix4 mutants with either Fo5176-SIX4 or Fol-SIX4. Thus, Fo5176-SIX4 contributes quantitatively to virulence on Arabidopsis whereas, in tomato, Fol-SIX4 acts in host specificity as both an avirulence protein and a suppressor of other race-specific resistances. The strong sequence conservation for SIX4 in F. oxysporum f. sp. lycopersici and Fo5176 suggests a recent common origin.

Auxin signaling and transport promote susceptibility to the root-infecting fungal pathogen Fusarium oxysporum in Arabidopsis.

Fusarium oxysporum is a root-infecting fungal pathogen that causes wilt disease on a broad range of plant species, including the model plant Arabidopsis thaliana. Currently, very little is known about the molecular or physiological processes that are activated in the host during infection and the roles these processes play in resistance and susceptibility to F. oxysporum. In this study, we analyzed global gene expression profiles of F. oxysporum-infected Arabidopsis plants. Genes involved in jasmonate biosynthesis as well as jasmonate-dependent defense were coordinately induced by F. oxysporum. Similarly, tryptophan pathway genes, including those involved in both indole-glucosinolate and auxin biosynthesis, were upregulated in both the leaves and the roots of inoculated plants. Analysis of plants expressing the DR5:GUS construct suggested that root auxin homeostasis was altered during F. oxysporum infection. However, Arabidopsis mutants with altered auxin and tryptophan-derived metabolites such as indole-glucosinolates and camalexin did not show an altered resistance to this pathogen. In contrast, several auxin-signaling mutants were more resistant to F. oxysporum. Chemical or genetic alteration of polar auxin transport also conferred increased pathogen resistance. Our results suggest that, similarly to many other pathogenic and nonpathogenic or beneficial soil organisms, F. oxysporum requires components of auxin signaling and transport to colonize the plant more effectively. Potential mechanisms of auxin signaling and transport-mediated F. oxysporum susceptibility are discussed.

Tackling Control of a Cosmopolitan Phytopathogen: Sclerotinia.

Phytopathogenic members of the Sclerotinia genus cause widespread disease across a broad range of economically important crops. In particular, Sclerotinia sclerotiorum is considered one of the most destructive and cosmopolitan of plant pathogens. Here, were review the epidemiology of the pathogen, its economic impact on agricultural production, and measures employed toward control of disease. We review the broad approaches required to tackle Sclerotinia diseases and include cultural practices, crop genetic resistance, chemical fungicides, and biological controls. We highlight the benefits and drawbacks of each approach along with recent advances within these controls and future strategies.

Developing Actinobacterial Endophytes as Biocontrol Products for Fusarium pseudograminearum in Wheat.

Crown rot of wheat, caused by Fusarium pseudograminearum, results in millions of dollars of yield losses globally each year. Management strategies to control crown rot are limited and there are concerns about development of fungicide resistance so novel treatment strategies are desirable. A collection of endophytic Actinobacteria was screened for their ability to suppress the growth of F. pseudograminearum and the development of crown rot symptoms in wheat with the aim of identifying candidates that can be developed into biocontrol products. The ability of the Actinobacteria isolates to suppress the growth of three different F. pseudograminearum strains in vitro was assessed using agar-plate competition assays. Soil-free seedling assays were used to screen for suppression of development of early disease symptoms in the susceptible wheat (Triticum aestivum) cv. Tamaroi. Four of the isolates were tested in a glasshouse pot experiment to assess their ability to decrease disease symptoms and prevent yield losses in wheat cv. Tamaroi grown to maturity in an unsterilized soil. The screening of 53 isolates identified two Streptomyces isolates, MH71 and MH243, with very strong antifungal activity against F. pseudograminearum strains in agar-plate competition and seedling assays. In the glasshouse pot trial, plants treated with seed coatings of either MH71 or MH243 had > 24% lower disease severity than control plants infected with F. pseudograminearum. These two cultures show potential for development as biocontrol products because they are easy to culture, grow on relatively inexpensive media, produce highly durable spores and can be delivered to plants as a seed coat.

A Plant Stress-Responsive Bioreporter Coupled With Transcriptomic Analysis Allows Rapid Screening for Biocontrols of Necrotrophic Fungal Pathogens.

Streptomyces are soil-borne Actinobacteria known to produce a wide range of enzymes, phytohormones, and metabolites including antifungal compounds, making these microbes fitting for use as biocontrol agents in agriculture. In this study, a plant reporter gene construct comprising the biotic stress-responsive glutathione S-transferase promoter GSTF7 linked to a luciferase output (GSTF7:luc) was used to screen a collection of Actinobacteria candidates for manipulation of plant biotic stress responses and their potential as biocontrol agents. We identified a Streptomyces isolate (KB001) as a strong candidate and demonstrated successful protection against two necrotrophic fungal pathogens, Sclerotinia sclerotiorum and Rhizoctonia solani, but not against a bacterial pathogen (Pseudomonas syringe). Treatment of Arabidopsis plants with either KB001 microbial culture or its secreted compounds induced a range of stress and defense response-related genes like pathogenesis-related (PR) and hormone signaling pathways. Global transcriptomic analysis showed that both treatments shared highly induced expression of reactive oxygen species and auxin signaling pathways at 6 and 24 h posttreatment, while some other responses were treatment specific. This study demonstrates that GSTF7 is a suitable marker for the rapid and preliminary screening of beneficial bacteria and selection of candidates with potential for application as biocontrols in agriculture, including the Streptomyces KB001 that was characterized here, and could provide protection against necrotrophic fungal pathogens.

A method for high-throughput image-based antifungal screening.

Robust antifungal screening is technically challenging particularly for filamentous fungi. We present a method for undertaking antifungal screening assays that builds upon existing broth dilution protocols and incorporates time resolved image-based assessment of fungal growth. We show that the method performs with different fungi, particularly those for which spores can be used as inoculum, and with different compound classes, can accurately assess susceptibility or otherwise in only few hours and can even account for differences in inherent growth properties of strains.

Fusarium oxysporum hijacks COI1-mediated jasmonate signaling to promote disease development in Arabidopsis.

Although defense responses mediated by the plant oxylipin jasmonic acid (JA) are often necessary for resistance against pathogens with necrotrophic lifestyles, in this report we demonstrate that jasmonate signaling mediated through COI1 in Arabidopsis thaliana is responsible for susceptibility to wilt disease caused by the root-infecting fungal pathogen Fusarium oxysporum. Despite compromised JA-dependent defense responses, the JA perception mutant coronatine insensitive 1 (coi1), but not JA biosynthesis mutants, exhibited a high level of resistance to wilt disease caused by F. oxysporum. This response was independent from salicylic acid-dependent defenses, as coi1/NahG plants showed similar disease resistance to coi1 plants. Inoculation of reciprocal grafts made between coi1 and wild-type plants revealed that coi1-mediated resistance occurred primarily through the coi1 rootstock tissues. Furthermore, microscopy and quantification of fungal DNA during infection indicated that coi1-mediated resistance was not associated with reduced fungal penetration and colonization until a late stage of infection, when leaf necrosis was highly developed in wild-type plants. In contrast to wild-type leaves, coi1 leaves showed no necrosis following the application of F. oxysporum culture filtrate, and showed reduced expression of senescence-associated genes during disease development, suggesting that coi1 resistance is most likely achieved through the inhibition of F. oxysporum-incited lesion development and plant senescence. Together, our results indicate that F. oxysporum hijacks non-defensive aspects of the JA-signaling pathway to cause wilt-disease symptoms that lead to plant death in Arabidopsis.

A functional genomics approach to dissect spotted alfalfa aphid resistance in Medicago truncatula.

Aphids are virus-spreading insect pests affecting crops worldwide and their fast population build-up and insecticide resistance make them problematic to control. Here, we aim to understand the molecular basis of spotted alfalfa aphid (SAA) or Therioaphis trifolii f. maculata resistance in Medicago truncatula, a model organism for legume species. We compared susceptible and resistant near isogenic Medicago lines upon SAA feeding via transcriptome sequencing. Expression of genes involved in defense and stress responses, protein kinase activity and DNA binding were enriched in the resistant line. Potentially underlying some of these changes in gene expression was the finding that members of the MYB, NAC, AP2 domain and ERF transcription factor gene families were differentially expressed in the resistant versus susceptible lines. A TILLING population created in the resistant cultivar was screened using exome capture sequencing and served as a reverse genetics tool to functionally characterise genes involved in the aphid resistance response. This screening revealed three transcription factors (a NAC, AP2 domain and ERF) as important regulators in the defence response, as a premature stop-codon in the resistant background led to a delay in aphid mortality and enhanced plant susceptibility. This combined functional genomics approach will facilitate the future development of pest resistant crops by uncovering candidate target genes that can convey enhanced aphid resistance.

The Arabidopsis altered in stress response2 is Impaired in Resistance to Root and Leaf Necrotrophic Fungal Pathogens.

The Arabidopsis thaliana Glutathione S-transferase Phi8 (GSTF8) gene is recognised as a marker for early defence and stress responses. To identify regulators of these responses, a forward genetic screen for Arabidopsis mutants with up-regulated GSTF8 promoter activity was conducted by screening a mutagenized population containing a GSTF8 promoter fragment fused to the luciferase reporter gene (GSTF8:LUC). We previously identified several enhanced stress response (esr) mutants from this screen that conferred constitutive GSTF8:LUC activity and increased resistance to several pathogens and/or insects pests. Here we identified a further mutant constitutively expressing GSTF8:LUC and termed altered in stress response2 (asr2). Unlike the esr mutants, asr2 was more susceptible to disease symptom development induced by two necrotrophic fungal pathogens; the root pathogen Fusarium oxysporum, and the leaf pathogen Alternaria brassicicola. The asr2 allele was mapped to a 2.1 Mbp region of chromosome 2 and narrowed to four candidate loci.

Draft Genome Sequences of Streptomyces sp. Strains MH60 and 111WW2.

We report here the draft genome sequences, annotations, and predictions of secondary metabolite gene clusters of two endophytic Streptomyces species isolated from wheat plants growing in the Western Australian wheat belt. These strains, Streptomyces sp. strains MH60 and 111WW2, possess antifungal and/or plant growth-promoting activities.

The Arabidopsis RNA Polymerase II Carboxyl Terminal Domain (CTD) Phosphatase-Like1 (CPL1) is a biotic stress susceptibility gene.

Crop breeding for improved disease resistance may be achieved through the manipulation of host susceptibility genes. Previously we identified multiple Arabidopsis mutants known as enhanced stress response1 (esr1) that have defects in a KH-domain RNA-binding protein and conferred increased resistance to the root fungal pathogen Fusarium oxysporum. Here, screening the same mutagenized population we discovered two further enhanced stress response mutants that also conferred enhanced resistance to F. oxysporum. These mutants also have enhanced resistance to a leaf fungal pathogen (Alternaria brassicicola) and an aphid pest (Myzus persicae), but not to the bacterial leaf pathogen Pseudomonas syringae. The causal alleles in these mutants were found to have defects in the ESR1 interacting protein partner RNA Polymerase II Carboxyl Terminal Domain (CTD) Phosphatase-Like1 (CPL1) and subsequently given the allele symbols cpl1-7 and cpl1-8. These results define a new role for CPL1 as a pathogen and pest susceptibility gene. Global transcriptome analysis and oxidative stress assays showed these cpl1 mutants have increased tolerance to oxidative stress. In particular, components of biotic stress responsive pathways were enriched in cpl1 over wild-type up-regulated gene expression datasets including genes related to defence, heat shock proteins and oxidative stress/redox state processes.