A pigeonpea gene confers resistance to Asian soybean rust in soybean

Salicylic acid-dependent immunity contributes to resistance against Rhizoctonia solani, a necrotrophic fungal agent of sheath blight, in rice and Brachypodium distachyon

Rhizoctonia solani is a soil-borne fungus causing sheath blight. In consistent with its necrotrophic life style, no rice cultivars fully resistant to R. solani are known, and agrochemical plant defense activators used for rice blast, which upregulate a phytohormonal salicylic acid (SA)-dependent pathway, are ineffective towards this pathogen. As a result of the unavailability of genetics, the infection process of R. solani remains unclear. We used the model monocotyledonous plants Brachypodium distachyon and rice, and evaluated the effects of phytohormone-induced resistance to R. solani by pharmacological, genetic and microscopic approaches to understand fungal pathogenicity. Pretreatment with SA, but not with plant defense activators used in agriculture, can unexpectedly induce sheath blight resistance in plants. SA treatment inhibits the advancement of R. solani to the point in the infection process in which fungal biomass shows remarkable expansion and specific infection machinery is developed. The involvement of SA in R. solani resistance is demonstrated by SA-deficient NahG transgenic rice and the sheath blight-resistant B. distachyon accessions, Bd3-1 and Gaz-4, which activate SA-dependent signaling on inoculation. Our findings suggest a hemi-biotrophic nature of R. solani, which can be targeted by SA-dependent plant immunity. Furthermore, B. distachyon provides a genetic resource that can confer disease resistance against R. solani to plants.

Signaling Mechanisms Underlying Resistance Responses: What Have We Learned, and How Is It Being Applied?

Plants have evolved highly specific mechanisms to resist pathogens including preformed barriers and the induction of elaborate signaling pathways. Induced signaling requires recognition of the pathogen either via conserved pathogen-derived factors or specific pathogen-encoded proteins called effectors. Recognition of these factors by host encoded receptor proteins can result in the elicitation of different tiers of resistance at the site of pathogen infection. In addition, plants induce a type of systemic immunity which is effective at the whole plant level and protects against a broad spectrum of pathogens. Advances in our understanding of pathogen-recognition mechanisms, identification of the underlying molecular components, and their significant conservation across diverse plant species has enabled the development of novel strategies to combat plant diseases. This review discusses key advances in plant defense signaling that have been adapted or have the potential to be adapted for plant protection against microbial diseases.

Transfer and engineering of immune receptors to improve recognition capacities in crops

Immune receptors are pivotal elements of the plant immune system that act as sentinels for microbial invasion. Knowingly or unknowingly, breeding for resistance has largely relied on the transfer of immune receptor recognition specificities between plant genotypes. For decades such transfers were limited to crossable species. However, advents in transgene technologies have allowed overcoming species barriers. Novel strategies for mining of recognition specificities, combined with our recently increased understanding of immune receptor functioning, allows to increase and alter recognition specificities, which should ultimately increase the spectrum of recognition specificities that are available to control plant diseases in crops.

Comparative analysis of targeted long read sequencing approaches for characterization of a plant's immune receptor repertoire

BACKGROUND

The Oxford Nanopore Technologies MinION™ sequencer is a small, portable, low cost device that is accessible to labs of all sizes and attractive for in-the-field sequencing experiments. Selective breeding of crops has led to a reduction in genetic diversity, and wild relatives are a key source of new genetic resistance to pathogens, usually via NLR immune receptor-encoding genes. Recent studies have demonstrated how crop NLR repertoires can be targeted for sequencing on Illumina or PacBio (RenSeq) and the specific gene conveying pathogen resistance identified.

RESULTS

Sequence yields per MinION run are lower than Illumina, making targeted resequencing an efficient approach. While MinION generates long reads similar to PacBio it doesn't generate the highly accurate multipass consensus reads, which presents downstream bioinformatics challenges. Here we demonstrate how MinION data can be used for RenSeq achieving similar results to the PacBio and how novel NLR gene fusions can be identified via a Nanopore RenSeq pipeline.

CONCLUSION

The described library preparation and bioinformatics methods should be applicable to other gene families or any targeted long DNA fragment nanopore sequencing project.

Fine Mapping and Transcriptome Analysis Reveal Candidate Genes Associated with Hybrid Lethality in Cabbage (Brassica Oleracea)

Hybrid lethality is a deleterious phenotype that is vital to species evolution. We previously reported hybrid lethality in cabbage (Brassica oleracea) and performed preliminary mapping of related genes. In the present study, the fine mapping of hybrid lethal genes revealed that BoHL1 was located on chromosome C1 between BoHLTO124 and BoHLTO130, with an interval of 101 kb. BoHL2 was confirmed to be between insertion-deletion (InDels) markers HL234 and HL235 on C4, with a marker interval of 70 kb. Twenty-eight and nine annotated genes were found within the two intervals of BoHL1 and BoHL2, respectively. We also applied RNA-Seq to analyze hybrid lethality in cabbage. In the region of BoHL1, seven differentially expressed genes (DEGs) and five resistance (R)-related genes (two in common, i.e., Bo1g153320 and Bo1g153380) were found, whereas in the region of BoHL2, two DEGs and four R-related genes (two in common, i.e., Bo4g173780 and Bo4g173810) were found. Along with studies in which R genes were frequently involved in hybrid lethality in other plants, these interesting R-DEGs may be good candidates associated with hybrid lethality. We also used SNP/InDel analyses and quantitative real-time PCR to confirm the results. This work provides new insight into the mechanisms of hybrid lethality in cabbage.

Molecular Soybean-Pathogen Interactions

Soybean hosts a wide variety of pathogens that cause significant yield losses. The importance of soybean as a major oilseed crop has led to research focused on its interactions with pathogens, such as Soybean mosaic virus, Pseudomonas syringae, Phytophthora sojae, Phakopsora pachyrhizi, and Heterodera glycines. Pioneering work on soybean's interactions with these organisms, which represent the five major pathogen groups (viruses, bacteria, oomycetes, fungi, and nematodes), has contributed to our understanding of the molecular mechanisms underlying virulence and immunity. These mechanisms involve conserved and unique features that validate the need for research in both soybean and homologous model systems. In this review, we discuss identification of effectors and their functions as well as resistance gene-mediated recognition and signaling. We also point out areas in which model systems and recent advances in resources and tools have provided opportunities to gain deeper insights into soybean-pathogen interactions.