The Odilorhabdin Antibiotic Biosynthetic Cluster and Acetyltransferase Self-Resistance Locus Are Niche and Species Specific

Odilorhabdins (ODLs) constitute a novel antibiotic family with promising properties for treating problematic multidrug-resistant Gram-negative bacterial infections. ODLs are 10-mer linear cationic peptides inhibiting bacterial translation by binding to the small subunit of the ribosome.

Brassica napus genes Rlm4 and Rlm7, conferring resistance to Leptosphaeria maculans, are alleles of the Rlm9 wall-associated kinase-like resistance locus

Brassica napus (canola/rapeseed) race specific resistance genes against blackleg disease, caused by the ascomycete fungus Leptosphaeria maculans, have been commonly used in canola breeding. To date, LepR3, Rlm2 and Rlm9 R genes against L. maculans have been cloned from B. napus. LepR3 and Rlm2 are Receptor Like Proteins (RLP) and the recently reported Rlm9 is a Wall Associated Kinase-Like (WAKL) protein. Rlm9 located on chromosome A07 is closely linked with Rlm3, Rlm4, RLm7 genes. Recognition of AvrLm5-9 and AvrLm3 by their corresponding Rlm9 and Rlm3 proteins is masked in the presence of AvrLm4-7. Here we report cloning of Rlm4 and Rlm7 by generating genome sequence of the doubled haploid (DH) B. napus cv Topas DH16516 introgression lines Topas-Rlm4 and Topas-Rlm7. Candidate Rlm4 and Rlm7 genes were identified form the genome sequence and gene structures were determined by mapping RNA-sequence reads, generated from infected cotyledon tissues, to the genome of Topas-Rlm4 and Topas-Rlm7. Rlm4 and Rlm7 genomic constructs with their native promoters were transferred into the blackleg susceptible B. napus cv Westar. Complementation of resistance response in the transgenic Westar-Rlm4 and Westar-Rlm7 that were inoculated with L. maculans transgenic isolates 2367-AvrRlm4-7 or 2367-AvrLm7 confirmed the function of Rlm4 and Rlm7 genes. Wild type L. maculans isolate 2367 that does not contain AvrLm4-7 or AvrLm7, and transgenic 2367-AvrLm3 and 2367-AvrLm5-9 did not induce resistance proving the specificity of Rlm4 and Rlm7 response. Rlm4 and Rlm7 alleles are also allelic to Rlm9. Rlm4 and Rlm7 genes encode WAKL proteins. Comparison of highly-homologous sequences of Rlm4 and Rlm7 with each other and with the sequence of additional alleles identified a limited number of point mutation located within the predicted extracellular receptor domains.

SGT1 SGS-domain mutations impair interactions with the barley MLA6 immune receptor in association with loss of NLR protein

The Mla (Mildew resistance locus a) of barley (Hordeum vulgare L.) is an effective model for cereal immunity against fungal pathogens. Like many resistance proteins, variants of the MLA coiled-coil nucleotide-binding leucine-rich-repeat (CC-NLR) receptor require the HRS complex to function, which includes HSP90 (Heat Shock Protein 90), RAR1 (Required for Mla12 Resistance 1), and SGT1 (Suppressor of G-two allele of Skp1). However, functional analysis of Sgt1 has been particularly difficult as deletions are often lethal. Recently, we identified rar3 (Required for Mla6 resistance 3), an in-frame Sgt1ΔKL308-309 mutation in the SGS domain that alters resistance conferred by MLA, but without lethality. Here we use autoactive MLA6 and heterologous yeast-two-hybrid strains with stably integrated HvRar1 and HvHsp90, to determine that this mutation weakens, but doesn’t entirely disrupt, the interaction between SGT1 and MLA. This causes a concomitant reduction in MLA6 protein accumulation below the apparent threshold required for effective resistance. The ΔKL308-309 deletion had a lesser effect on intramolecular interactions than alanine or arginine substitutions, and MLA variants that display diminished interactions with SGT1 appear to be disproportionately affected by the SGT1ΔKL308-309 mutation. We hypothesize that those dimeric plant CC-NLRs that appear unaffected by Sgt1 silencing are those with the strongest intermolecular interactions with it. Combining our data with recent work in CC-NLRs, we propose a cyclical model of the MLA-HRS resistosome interactions.

The UV RESISTANCE LOCUS 8-Mediated UV-B Response Is Required Alongside CRYPTOCHROME1 For Plant Survival Under Sunlight In The Field

As sessile organisms, plants are subjected to fluctuating sunlight including potentially detrimental ultraviolet-B radiation (UV-B). In Arabidopsis thaliana, experiments under controlled conditions have shown that UV RESISTANCE LOCUS 8 (UVR8) controls photomorphogenic responses for acclimation and tolerance to UV-B; however, its long-term impacts on plant performance remain poorly understood in naturally fluctuating environments. Here we quantified the survival and reproduction of different Arabidopsis mutant genotypes in diverse field and laboratory conditions. We found that uvr8 mutants produced more fruits than wild type in growth chambers with artificial low UV-B conditions but not in natural field conditions. Importantly, independent double mutants of UVR8 and the blue-light photoreceptor gene CRYPTOCHROME 1 (CRY1) in two genetic backgrounds showed a drastic reduction in fitness in the field. UV-B attenuation experiments in field conditions and supplemental UV-B in growth chambers demonstrated that UV-B caused the conditional cry1 uvr8 lethality phenotype. RNA sequencing in different conditions revealed a large number of genes with statistical interaction of UVR8 and CRY1 mutations in the presence of UV-B in the field. Among them, Gene Ontology analysis identified enrichment of categories related to UV-B response, oxidative stress, photoprotection and DNA damage repair. Our study demonstrates the functional importance of the UVR8-mediated response across life stages in natura, which is partially redundant with CRY1, and provides an integral picture of gene expression associated with plant environmental responses under diverse environmental conditions.

Genetic Dissection of the Breakdown of Durable Resistance in Indica Rice Variety PTB33 to Brown Planthoppers Nilaparvata Lugens (Stål)

BackgroundTo avoid and delay the resistance breakdown of varieties against pathogens and insect pests, broad-spectrum and durable resistance by multiple genes pyramiding are expected to be one of the practical approaches. The indica rice variety PTB33 (Oryza sativa L.) shows high and durable resistance to the brown planthopper (BPH, Nilaparvata lugens Stål). However, this variety gradually lost its resistance against the recent virulence development of BPH. However, breakdown processes are not fully elucidated by individual genetic loci. ResultsEffective QTLs were explored across the whole genomic region against four BPH populations collected in Japan in 1988, 1989, 1999, and 2013 using high-density single-nucleotide polymorphism (SNP) markers obtained by genotyping-by-sequencing. Among seven genomic regions of PTB33 likely conferring BPH resistance, four QTLs, qFSA4a, qFSA6, qFSA11, and qFSA12 on chromosomes 4, 6, 11, and 12, respectively, were validated as BPH resistance QTLs. The PTB33 alleles at the four QTLs positively contributed to BPH resistance. Infestation of monogenic segregating lines showed that the PTB33 alleles at qFSA11, qFSA12, and qFSA4a lost resistance effects at least in 1989, 1999, and 2013, respectively. ConclusionThis study showed breakdown of durable resistance in PTB33 was explained by step-by-step losses of genetic effects at each resistance locus and probably multiple acquisitions of virulence genes in BPH in a gene-by-gene specific manner.

Discovery of a novel powdery mildew (Blumeria graminis) resistance locus in rye (Secale cereale L.)

Powdery mildew is one of the most destructive diseases in the world, causing substantial grain yield losses and quality reduction in cereal crops. At present 23 powdery mildew resistance genes have been identified in rye, of which the majority are in wheat-rye translocation lines developed for wheat improvement. Here, we investigated the genetics underlying powdery mildew resistance in the Gülzow-type elite hybrid rye (Secale cereale L.) breeding germplasm. In total, 180 inbred breeding lines were genotyped using the state-of-the-art 600 K SNP array and phenotyped for infection type against three distinct field populations of B. graminis f. sp. secalis from Northern Germany (2013 and 2018) and Denmark (2020). We observed a moderate level of powdery mildew resistance in the non-restorer germplasm population, and by performing a genome-wide association study using 261,406 informative SNP markers, we identified a powdery mildew resistance locus, provisionally denoted PmNOS1, on the distal tip of chromosome arm 7RL. Using recent advances in rye genomic resources, we investigated whether nucleotide-binding leucine-rich repeat genes residing in the identified 17 Mbp block associated with PmNOS1 on recent reference genomes resembled known Pm genes.

Construction of a high-density genetic map and detection of a major QTL of resistance to powdery mildew (Erysiphe necator Sch.) in Caucasian grapes (Vitis vinifera L.)

Background Vitis vinifera L. is the most cultivated grapevine species worldwide. Erysiphe necator Sch., the causal agent of grape powdery mildew, is one of the main pathogens affecting viticulture. V. vinifera has little or no genetic resistances against E. necator and the grape industry is highly dependent on agrochemicals. Some Caucasian V. vinifera accessions have been reported to be resistant to E. necator and to have no genetic relationships to known sources of resistance to powdery mildew. The main purpose of this work was the study and mapping of the resistance to E. necator in the Caucasian grapes ‘Shavtsitska’ and ‘Tskhvedianis tetra’. Results The Caucasian varieties ‘Shavtsitska’ and ‘Tskhvedianis tetra’ showed a strong partial resistance to E. necator which segregated in two cross populations: the resistant genotypes delayed and limited the pathogen mycelium growth, sporulation intensity and number of conidia generated. A total of 184 seedlings of ‘Shavtsitska’ x ‘Glera’ population were genotyped through the Genotyping by Sequencing (GBS) technology and two high-density linkage maps were developed for the cross parents. The QTL analysis revealed a major resistance locus, explaining up to 80.15% of the phenotypic variance, on ‘Shavtsitska’ linkage group 13, which was associated with a reduced pathogen infection as well as an enhanced plant necrotic response. The genotyping of 105 Caucasian accessions with SSR markers flanking the QTL revealed that the resistant haplotype of ‘Shavtsitska’ was shared by ‘Tskhvedianis tetra’ and a total of 25 Caucasian grape varieties, suggesting a widespread presence of this resistance in the surveyed germplasm. The uncovered QTL was mapped in the region where the Ren1 locus of resistance to E. necator, identified in the V. vinifera ‘Kishmish vatkana’ and related grapes of Central Asia, is located. The genetic analysis conducted revealed that the Caucasian grapes in this study exhibit a resistant haplotype different from that of Central Asian grape accessions. Conclusions The QTL isolated in ‘Shavtsitska’ and present in the Caucasian V. vinifera varieties could be a new candidate gene of resistance to E. necator to use in breeding programmes. It co-localizes with the Ren1 locus but shows a different haplotype from that of grapevines of Central Asia. We therefore consider that the Caucasian resistance locus, named Ren1.2, contains a member of a cluster of R-genes, of which the region is rich, and to be linked with, or possibly allelic, to Ren1.

Centenary of Soil and Air Borne Wheat Karnal Bunt Disease Research: A Review

Karnal bunt (KB) of wheat (Triticum aestivum L.), known as partial bunt has its origin in Karnal, India and is caused by Tilletia indica (Ti). Its incidence had grown drastically since late 1960s from northwestern India to northern India in early 1970s. It is a seed, air and soil borne pathogen mainly affecting common wheat, durum wheat, triticale and other related species. The seeds become inedible, inviable and infertile with the precedence of trimethylamine secreted by teliospores in the infected seeds. Initially the causal pathogen was named Tilletia indica but was later renamed Neovossia indica. The black powdered smelly spores remain viable for years in soil, wheat straw and farmyard manure as primary sources of inoculum. The losses reported were as high as 40% in India and also the cumulative reduction of national farm income in USA was USD 5.3 billion due to KB. The present review utilizes information from literature of the past 100 years, since 1909, to provide a comprehensive and updated understanding of KB, its causal pathogen, biology, epidemiology, pathogenesis, etc. Next generation sequencing (NGS) is gaining popularity in revolutionizing KB genomics for understanding and improving agronomic traits like yield, disease tolerance and disease resistance. Genetic resistance is the best way to manage KB, which may be achieved through detection of genes/quantitative trait loci (QTLs). The genome-wide association studies can be applied to reveal the association mapping panel for understanding and obtaining the KB resistance locus on the wheat genome, which can be crossed with elite wheat cultivars globally for a diverse wheat breeding program. The review discusses the current NGS-based genomic studies, assembly, annotations, resistant QTLs, GWAS, technology landscape of diagnostics and management of KB. The compiled exhaustive information can be beneficial to the wheat breeders for better understanding of incidence of disease in endeavor of quality production of the crop.

Phenotypic Characterization and Molecular Mapping of Recessive Resistance To Meloidogyne Javanica in Cucumber, Cucumis Sativus

The Javanese root-knot nematode (JRKN, Meloidogyne javanica) is a serious pest of cucumber (Cucumis sativus) grown in tropical and subtropical regions. The recessive mj resistance gene first identified in the wild cucumber (C. sativus var. hardwickii), is the only known source of resistance to JRKN within the C. sativus gene pool. Despite its potential utility as a nematode management tool, the mj trait has yet to be fully characterized or widely incorporated into commercial cucumber lines. In this study, we mapped the mj resistance locus to a 148-kb interval on cucumber chromosome 1 by phenotyping a recombinant inbred line (RIL) and targeted backcross populations. The genomic interval is predicted to contain 36 candidate genes, including several known to be directly related to plant defense against pathogens. We also conducted histological comparisons of nematode development in mj resistant and susceptible lines, providing evidence that the mechanism of action for this gene may be different from that of known RKN resistance genes. These results provide a set of tightly linked markers that can assist breeding programs seeking to incorporate mj resistance into new cucumber varieties. The candidate genes will also provide a starting point for further research into the mechanisms of action that underlay the mj-regulated JRKN resistance.