Arabidopsis non-host resistance PSS30 gene enhances broad-spectrum disease resistance in the soybean cultivar Williams 82

Non-host resistance (NHR), which protects all members of a plant species from non-adapted or non-host plant pathogens, is the most common form of plant immunity. NHR provides the most durable and robust form of broad-spectrum immunity against non-adaptive pathogens pathogenic to other crop species. In a mutant screen for loss of Arabidopsis (Arabidopsis thaliana) NHR against the soybean (Glycine max (L.) Merr.) pathogen Phytophthora sojae, the Phytophthora sojae-susceptible 30 (pss30) mutant was identified. The pss30 mutant is also susceptible to the soybean pathogen Fusarium virguliforme. PSS30 encodes a folate transporter, AtFOLT1, which was previously localized to chloroplasts and implicated in the transport of folate from the cytosol to plastids. We show that two Arabidopsis folate biosynthesis mutants with reduced folate levels exhibit a loss of non-host immunity against P. sojae. As compared to the wild-type Col-0 ecotype, the steady-state folate levels are reduced in the pss1, atfolt1 and two folate biosynthesis mutants, suggesting that folate is required for non-host immunity. Overexpression of AtFOLT1 enhances immunity of transgenic soybean lines against two serious soybean pathogens, the fungal pathogen F. virguliforme and the soybean cyst nematode (SCN) Heterodera glycines. Transgenic lines showing enhanced SCN resistance also showed increased levels of folate accumulation. This study thus suggests that folate contributes to non-host plant immunity and that overexpression of a non-host resistance gene could be a suitable strategy for generating broad-spectrum disease resistance in crop plants.

Overexpression of a plasma membrane protein generated broad-spectrum immunity in soybean

Plants fight-off pathogens and pests by manifesting an array of defence responses using their innate immunity mechanisms. Here we report the identification of a novel soybean gene encoding a plasma membrane protein, transcription of which is suppressed following infection with the fungal pathogen, Fusarium virguliforme. Overexpression of the protein led to enhanced resistance against not only against F. virguliforme, but also against spider mites (Tetranychus urticae, Koch), soybean aphids (Aphis glycines, Matsumura) and soybean cyst nematode (Heterodera glycines). We, therefore, name this protein as Glycine max disease resistance 1 (GmDR1; Glyma.10g094800). The homologues of GmDR1 have been detected only in legumes, cocoa, jute and cotton. The deduced GmDR1 protein contains 73 amino acids. GmDR1 is predicted to contain an ecto- and two transmembrane domains. Transient expression of the green fluorescent protein fused GmDR1 protein in soybean leaves showed that it is a plasma membrane protein. We investigated if chitin, a pathogen-associated molecular pattern (PAMP), common to all pathogen and pests considered in this study, can significantly enhance defence pathways among the GmDR1-overexpressed transgenic soybean lines. Chitin induces marker genes of the salicylic- and jasmonic acid-mediated defence pathways, but suppresses the defence pathway regulated by ethylene. Chitin induced SA- and JA-regulated defence pathways may be one of the mechanisms involved in generating broad-spectrum resistance among the GmDR1-overexpressed transgenic soybean lines against two serious pathogens and two pests including spider mites, against which no known resistance genes have been identified in soybean and among the most other crop species.

Arabidopsis Novel Glycine-Rich Plasma Membrane PSS1 Protein Enhances Disease Resistance in Transgenic Soybean Plants

Nonhost resistance is defined as the immunity of a plant species to all nonadapted pathogen species. Arabidopsis (Arabidopsis thaliana) ecotype Columbia-0 is nonhost to the oomycete plant pathogen Phytophthora sojae and the fungal plant pathogen Fusarium virguliforme that are pathogenic to soybean (Glycine max). Previously, we reported generating the pss1 mutation in the pen1-1 genetic background as well as genetic mapping and characterization of the Arabidopsis nonhost resistance Phytophthora sojae-susceptible gene locus, PSS1 In this study, we identified six candidate PSS1 genes by comparing single-nucleotide polymorphisms of (1) the bulked DNA sample of seven F2:3 families homozygous for the pss1 allele and (2) the pen1-1 mutant with Columbia-0. Analyses of T-DNA insertion mutants for each of these candidate PSS1 genes identified the At3g59640 gene encoding a glycine-rich protein as the putative PSS1 gene. Later, complementation analysis confirmed the identity of At3g59640 as the PSS1 gene. PSS1 is induced following P. sojae infection as well as expressed in an organ-specific manner. Coexpression analysis of the available transcriptomic data followed by reverse transcriptase-polymerase chain reaction suggested that PSS1 is coregulated with ATG8a (At4g21980), a core gene in autophagy. PSS1 contains a predicted single membrane-spanning domain. Subcellular localization study indicated that it is an integral plasma membrane protein. Sequence analysis suggested that soybean is unlikely to contain a PSS1-like defense function. Following the introduction of PSS1 into the soybean cultivar Williams 82, the transgenic plants exhibited enhanced resistance to F. virguliforme, the pathogen that causes sudden death syndrome.

Tanscriptomic Study of the Soybean-Fusarium virguliforme Interaction Revealed a Novel Ankyrin-Repeat Containing Defense Gene, Expression of Whose during Infection Led to Enhanced Resistance to the Fungal Pathogen in Transgenic Soybean Plants

Fusarium virguliforme causes the serious disease sudden death syndrome (SDS) in soybean. Host resistance to this pathogen is partial and is encoded by a large number of quantitative trait loci, each conditioning small effects. Breeding SDS resistance is therefore challenging and identification of single-gene encoded novel resistance mechanisms is becoming a priority to fight this devastating this fungal pathogen. In this transcriptomic study we identified a few putative soybean defense genes, expression of which is suppressed during F. virguliforme infection. The F. virguliforme infection-suppressed genes were broadly classified into four major classes. The steady state transcript levels of many of these genes were suppressed to undetectable levels immediately following F. virguliforme infection. One of these classes contains two novel genes encoding ankyrin repeat-containing proteins. Expression of one of these genes, GmARP1, during F. virguliforme infection enhances SDS resistance among the transgenic soybean plants. Our data suggest that GmARP1 is a novel defense gene and the pathogen presumably suppress its expression to establish compatible interaction.