Robert Heinz

A soybean cyst nematode resistance gene points to a new mechanism of plant resistance to pathogens

Soybean (Glycine max (L.) Merr.) is an important crop that provides a sustainable source of protein and oil worldwide. Soybean cyst nematode (Heterodera glycines Ichinohe) is a microscopic roundworm that feeds on the roots of soybean and is a major constraint to soybean production. This nematode causes more than US

Variability in distribution and virulence phenotypes of Heterodera glycines in missouri during 2005

1 billion in yield losses annually in the United States alone, making it the most economically important pathogen on soybean. Although planting of resistant cultivars forms the core management strategy for this pathogen, nothing is known about the nature of resistance. Moreover, the increase in virulent populations of this parasite on most known resistance sources necessitates the development of novel approaches for control. Here we report the map-based cloning of a gene at the Rhg4 (for resistance to Heterodera glycines 4) locus, a major quantitative trait locus contributing to resistance to this pathogen. Mutation analysis, gene silencing and transgenic complementation confirm that the gene confers resistance. The gene encodes a serine hydroxymethyltransferase, an enzyme that is ubiquitous in nature and structurally conserved across kingdoms. The enzyme is responsible for interconversion of serine and glycine and is essential for cellular one-carbon metabolism. Alleles of Rhg4 conferring resistance or susceptibility differ by two genetic polymorphisms that alter a key regulatory property of the enzyme. Our discovery reveals an unprecedented plant resistance mechanism against a pathogen. The mechanistic knowledge of the resistance gene can be readily exploited to improve nematode resistance of soybean, an increasingly important global crop.

A virus-induced gene silencing method to study soybean cyst nematode parasitism in Glycine max

The soybean cyst nematode, Heterodera glycines, is a serious economic threat to soybean producers in Missouri. Periodic monitoring for the presence, population densities, and virulence phenotypes of H. glycines is essential for determining crop losses and devising management strategies implementing the use of resistant cultivars. A survey using area-frame sampling was conducted to determine the distribution and virulence phenotypes of H. glycines in Missouri during 2005. Two samples from each of 125 fields representing eight geographical regions of Missouri were collected; 243 samples were processed for extraction of cysts and eggs. In all, 49% of samples had detectable cyst nematode populations, which ranged from 138 to 85,250 eggs per 250 cm3 of soil. Race and H. glycines type tests were conducted on populations from 45 samples. Nearly 80% of the populations that were tested, irrespective of the region, were virulent on the indicator line plant introduction (PI) 88788, which is the source of resistance for most H. glycines-resistant cultivars. More than 70% of populations could reproduce on the indicator lines PI 88788, PI 209332, and PI 548316 (Cloud), indicating that soybean cultivars with resistance derived from these sources need to be carefully monitored and used only in rotation with nonhost crops and soybean cultivars with resistance from other sources. Approximately one-third of the populations, primarily in the southern regions of Missouri, could reproduce on PI 548402 (Peking), another common source of resistance. Fewer than 10% of the populations could reproduce on PI 90763, PI 437654, PI 89772, or PI 438489B, suggesting that these sources of resistance should be used in soybean breeding programs to develop H. glycines-resistant soybean cultivars.

Lack of predictable race shift in Heterodera glycines-infested field plots

BackgroundBean pod mottle virus (BPMV) based virus-induced gene silencing (VIGS) vectors have been developed and used in soybean for the functional analysis of genes involved in disease resistance to foliar pathogens. However, BPMV-VIGS protocols for studying genes involved in disease resistance or symbiotic associations with root microbes have not been developed.FindingsHere we describe a BPMV-VIGS protocol suitable for reverse genetic studies in soybean roots. We use this method for analyzing soybean genes involved in resistance to soybean cyst nematode (SCN). A detailed SCN screening pipeline is described.ConclusionsThe VIGS method described here provides a new tool to identify genes involved in soybean-nematode interactions. This method could be adapted to study genes associated with any root pathogenic or symbiotic associations.

Distribution and virulence phenotypes of Heterodera glycines in Missouri

Soybean cultivars with different sources of resistance to Heterodera glycines were grown at three locations initially infested with races 2, 3, and 6 in order to investigate H. glycines race shift in field populations. Each spring and fall, soil samples were taken from each plot and race tests were conducted to evaluate effects of cultivar and time of sampling. Field experiments were paired field plots rotated annually with corn since 1991. Cultivars included at the northern and central Missouri sites were Williams 82 (susceptible to H. glycines), Linford (PI 88788 source of resistance), MFA 9043 (Peking) replaced by Morsoy 9345 (Peking and PI 88788) from 1995 to 1997, and Jackson II (Peking + PI 88788) replaced by Asgrow 3431 (Peking and PI 88788) in 1996-97. Cultivars at the southern Missouri site were Essex or Hutcheson (susceptible to H. glycines), Forrest (Peking), Hartwig (PI 437654), and Rhodes (PI 88788 + Peking). In 1995, race tests were performed at four temperature regimes to determine temperature effects on race designations. Race shifts were not predictable based on the source of resistance of the soybean cultivar planted. Variability in female numbers on Lee 74 among tests caused changes in female indices (FI). Furthermore, race designations were influenced by the time of sampling and temperature at which the race tests were conducted. The variability of H. glycines populations in both field and greenhouse situations diminishes the value of race test results when making cultivar recommendations.

The soybean GmSNAP18 gene underlies two types of resistance to soybean cyst nematode

The soybean cyst nematode, Heterodera glycines, is the most economically important pathogen of soybean in Missouri. Knowledge of the nematodes distribution and ability to adapt to resistant varieties is important for determining crop losses and establishing research priorities. No previous surveys of Missouri have provided reliable population density and phenotypic diversity data; therefore, we conducted a random survey to obtain both. Two samples from each of 200 fields were collected; 392 samples were processed for extractions of cysts and eggs. Two hundred and forty seven (63%) of the samples had detectable cyst nematode populations, which ranged from 15 to 149,700 eggs per 250 cm3 of soil. The lowest average population densities were observed in the east-central region of Missouri (2,260 eggs per 250 cm3 of soil), and the highest were observed in the northeast (9,238 eggs per 250 cm3 of soil), but among the eight regions sampled, mean population densities did not differ significantly. These population densities were potentially responsible for losses worth over

The Arabidopsis immune regulator SRFR1 dampens defences against herbivory by Spodoptera exigua and parasitism by Heterodera schachtii

58 million in 1999 in Missouri. Race tests were conducted on populations from 183 samples. In order of frequency, races 3, 1, and 2 accounted for 86% of H. glycines populations. Nearly 60% of the populations were virulent (able to produce females) on plant introduction (PI) 88788, which is the source of resistance for most H. glycines-resistant cultivars. More than a third of the populations were virulent on cv. Peking, another common resistance source. Very few populations were virulent on PI 90763 or PI 437654, suggesting that these sources of resistance should be exploited more frequently.

Systematic Mutagenesis of Serine Hydroxymethyltransferase Reveals an Essential Role in Nematode Resistance

Two types of resistant soybean (Glycine max (L.) Merr.) sources are widely used against soybean cyst nematode (SCN, Heterodera glycines Ichinohe). These include Peking-type soybean, whose resistance requires both the rhg1-a and Rhg4 alleles, and PI 88788-type soybean, whose resistance requires only the rhg1-b allele. Multiple copy number of PI 88788-type GmSNAP18, GmAAT, and GmWI12 in one genomic segment simultaneously contribute to rhg1-b resistance. Using an integrated set of genetic and genomic approaches, we demonstrate that the rhg1-a Peking-type GmSNAP18 is sufficient for resistance to SCN in combination with Rhg4. The two SNAPs (soluble NSF attachment proteins) differ by only five amino acids. Our findings suggest that Peking-type GmSNAP18 is performing a different role in SCN resistance than PI 88788-type GmSNAP18. As such, this is an example of a pathogen resistance gene that has evolved to underlie two types of resistance, yet ensure the same function within a single plant species.

Genetics and Adaptation of Soybean Cyst Nematode to Broad Spectrum Soybean Resistance

Summary Plants have developed diverse mechanisms to fine tune defence responses to different types of enemy. Cross‐regulation between signalling pathways may allow the prioritization of one response over another. Previously, we identified SUPPRESSOR OF rps4‐RLD 1 (SRFR 1) as a negative regulator of ENHANCED DISEASE SUSCEPTIBILITY1 (EDS1)‐dependent effector‐triggered immunity against the bacterial pathogen P seudomonas syringae pv. tomato strain DC3000 expressing avr R ps4. The use of multiple stresses is a powerful tool to further define gene function. Here, we examined whether SRFR 1 also impacts resistance to a herbivorous insect in leaves and to a cyst nematode in roots. Interestingly, srfr1‐1 plants showed increased resistance to herbivory by the beet army worm S podoptera exigua and to parasitism by the cyst nematode H eterodera schachtii compared with the corresponding wild‐type Arabidopsis accession RLD. Using quantitative real‐time PCR (qRT‐PCR) to measure the transcript levels of salicylic acid (SA) and jasmonate/ethylene (JA/ET) pathway genes, we found that enhanced resistance of srfr1‐1 plants to S. exigua correlated with specific upregulation of the MYC2 branch of the JA pathway concurrent with suppression of the SA pathway. In contrast, the greater susceptibility of RLD was accompanied by simultaneously increased transcript levels of SA, JA and JA/ET signalling pathway genes. Surprisingly, mutation of either SRFR 1 or EDS 1 increased resistance to H . schachtii, indicating that the concurrent presence of both wild‐type genes promotes susceptibility. This finding suggests a novel form of resistance in Arabidopsis to the biotrophic pathogen H . schachtii or a root‐specific regulation of the SA pathway by EDS1, and places SRFR 1 at an intersection between multiple defence pathways.

Distribution, Density, and Diversity of Heterodera glycines in Missouri.

A soybean serine hydroxymethyltransferase has a unique and essential role in soybean cyst nematode resistance. Rhg4 is a major genetic locus that contributes to soybean cyst nematode (SCN) resistance in the Peking-type resistance of soybean (Glycine max), which also requires the rhg1 gene. By map-based cloning and functional genomic approaches, we previously showed that the Rhg4 gene encodes a predicted cytosolic serine hydroxymethyltransferase (GmSHMT08); however, the novel gain of function of GmSHMT08 in SCN resistance remains to be characterized. Using a forward genetic screen, we identified an allelic series of GmSHMT08 mutants that shed new light on the mechanistic aspects of GmSHMT08-mediated resistance. The new mutants provide compelling genetic evidence that Peking-type rhg1 resistance in cv Forrest is fully dependent on the GmSHMT08 gene and demonstrates that this resistance is mechanistically different from the PI 88788-type of resistance that only requires rhg1. We also demonstrated that rhg1-a from cv Forrest, although required, does not exert selection pressure on the nematode to shift from HG type 7, which further validates the bigenic nature of this resistance. Mapping of the identified mutations onto the SHMT structural model uncovered key residues for structural stability, ligand binding, enzyme activity, and protein interactions, suggesting that GmSHMT08 has additional functions aside from its main enzymatic role in SCN resistance. Lastly, we demonstrate the functionality of the GmSHMT08 SCN resistance gene in a transgenic soybean plant.