TaNAC1 boosts powdery mildew resistance by phosphorylation-dependent regulation of TaSec1a and TaCAMTA4 via PP2Ac/CDPK20.

The integrity of wheat (Triticum aestivum) production is increasingly jeopardized by the fungal pathogen Blumeria graminis f. sp. tritici (Bgt), particularly amid the vicissitudes of climate change. Here, we delineated the role of a wheat transcription factor, TaNAC1, which precipitates cellular apoptosis and fortifies resistance against Bgt. Utilizing BiFC, co-immunoprecipitation, protein quantification, luciferase report assays, we determined that cytoplasmic TaNAC1-7A undergoes phosphorylation at the S184/S258 sites by TaCDPK20, facilitating its nuclear translocation. This migration appears to prime further phosphorylation by TaMPK1, thereby enhancing transcriptional regulatory activity. Notably, the apoptotic activity of phosphorylated TaNAC1-7A is negatively modulated by the nuclear protein phosphatase PP2Ac. Furthermore, activation of TaNAC1 phosphorylation initiates transcription of downstream genes TaSec1a and TaCAMTA4, through binding to the C[T/G]T[N7]A[A/C]G nucleic acid motif. Suppression of TaNAC1, TaCDPK20, and TaMPK1 in wheat compromises its resistance to Bgt strain E09, whereas overexpression of TaNAC1 and silencing of PP2Ac markedly elevate resistance levels. Our results reveal the pivotal role of TaNAC1 in basal resistance which is mediated by its effects on homotypic fusion, vacuolar protein sorting, and the expression of defense-related genes. The findings highlight the potential through targeting TaNAC1 and its regulators as a strategy for improving wheat's resistance to fungal pathogens.

Enhancing powdery mildew resistance in soybean by targeted mutation of MLO genes using the CRISPR/Cas9 system.

BACKGROUND: Powdery mildew is a major disease that causes great losses in soybean yield and seed quality. Disease-resistant varieties, which are generated by reducing the impact of susceptibility genes through mutation in host plants, would be an effective approach to protect crops from this disease. The Mildew Locus O (MLO) genes are well-known susceptibility genes for powdery mildew in plant. In this study, we utilized the CRISPR/Cas9 system to induce targeted mutations in the soybean GmMLO genes to improve powdery mildew resistance. RESULTS: A dual-sgRNA CRISPR/Cas9 construct was designed and successfully transferred into the Vietnamese soybean cultivar DT26 through Agrobacterium tumefaciens-mediated transformation. Various mutant forms of the GmMLO genes including biallelic, chimeric and homozygous were found at the T0 generation. The inheritance and segregation of CRISPR/Cas9-induced mutations were confirmed and validated at the T1 and T2 generations. Out of six GmMLO genes in the soybean genome, we obtained the Gmmlo02/Gmmlo19/Gmmlo23 triple and Gmmlo02/Gmmlo19/Gmmlo20/Gmmlo23 quadruple knockout mutants at the T2 generation. When challenged with Erysiphe diffusa, a fungus that causes soybean powdery mildew, all mutant plants showed enhanced resistance to the pathogen, especially the quadruple mutant. The powdery mildew severity in the mutant soybeans was reduced by up to 36.4% compared to wild-type plants. In addition, no pleiotropic effect on soybean growth and development under net-house conditions was observed in the CRISPR/Cas9 mutants. CONCLUSIONS: Our results indicate the involvement of GmMLO02, GmMLO19, GmMLO20 and GmMLO23 genes in powdery mildew susceptibility in soybean. Further research should be conducted to investigate the roles of individual tested genes and the involvement of other GmMLO genes in this disease infection mechanism. Importantly, utilizing the CRISPR/Cas9 system successfully created the Gmmlo transgene-free homozygous mutant lines with enhanced resistance to powdery mildew, which could be potential materials for soybean breeding programs.

Genome-wide identification of TaCIPK gene family members in wheat and their roles in host response to Blumeria graminis f. sp. tritici infection.

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is a destructive disease affecting wheat crops worldwide. Functional genes can be activated in response to Bgt inoculations. Calcineurin B-like protein (CBL) together with CBL-interacting protein kinase (CIPK) forms the CBL-CIPK protein complex that participates in Ca2+ sensor kinase-related signaling pathways responding to abiotic and biotic stresses. In this study, we performed a genome-wide screening and identified 27 CIPK subfamilies (123 CIPK transcripts, TaCIPKs) including 55 new and 47 updated TaCIPKs in wheat. Phylogenetic analysis revealed that 123 TaCIPKs could be divided into four groups. Segmental duplications and tandem repeats promoted the expansion of the TaCIPK family. Gene function was further evidenced by differences in gene structure, cis-elements, and protein domains. TaCIPK15-4A was cloned in this study. TaCIPK15-4A contained 17 serine, seven tyrosine, and 15 threonine phosphorylation sites and localized in the plasma membrane and cytoplasm. TaCIPK15-4A expression was induced after Bgt inoculation. Virus-induced gene silencing and overexpression experiments indicated that TaCIPK15-4A could play a positive role in wheat disease resistance to Bgt. Overall, these results provide insights into the role of the TaCIPK gene family in wheat resistance and could be beneficial for further research to prevent Bgt infection.

Highly effective mlo-based powdery mildew resistance in hexaploid wheat without pleiotropic effects.

Application of the mlo-based resistance in barley against powdery mildew attacks is a major success in crop breeding, since it confers durable disease resistance. Resistance caused by mutations in the Mlo gene seems to be ubiquitous across a range of species. This work addresses the introduction of mlo-based resistance into hexaploid wheat, which is complicated by the occurrence of three homoeologous genes: Mlo-A1, Mlo-B1 and Mlo-D1. EMS-generated mutant plants were screened for mutations in the three homoeologues. We selected and combined 6, 8, and 4 mutations, respectively, to obtain triple homozygous mlo mutant lines. Twenty-four mutant lines showed highly effective resistance towards attack by the powdery mildew pathogen under field conditions. All 18 mutations appeared to contribute to resistance; however, they had different effects on the occurrence of symptoms such as chlorotic and necrotic spots, which are pleiotropic to the mlo-based powdery mildew resistance. We conclude that to obtain highly effective powdery mildew resistance in wheat and to avoid detrimental pleiotropic effects, all three Mlo homoeologues should be mutated; however, at least one of the mutations should be of the weaker type in order to alleviate strong pleiotropic effects from the other mutations.

TaSYP137 and TaVAMP723, the SNAREs Proteins from Wheat, Reduce Resistance to Blumeria graminis f. sp. tritici.

SNARE protein is an essential factor driving vesicle fusion in eukaryotes. Several SNAREs have been shown to play a crucial role in protecting against powdery mildew and other pathogens. In our previous study, we identified SNARE family members and analyzed their expression pattern in response to powdery mildew infection. Based on quantitative expression and RNA-seq results, we focused on TaSYP137/TaVAMP723 and hypothesized that they play an important role in the interaction between wheat and Blumeria graminis f. sp. Tritici (Bgt). In this study, we measured the expression patterns of TaSYP132/TaVAMP723 genes in wheat post-infection with Bgt and found that the expression pattern of TaSYP137/TaVAMP723 was opposite in resistant and susceptible wheat samples infected by Bgt. The overexpression of TaSYP137/TaVAMP723 disrupted wheat's defense against Bgt infection, while silencing these genes enhanced its resistance to Bgt. Subcellular localization studies revealed that TaSYP137/TaVAMP723 are present in both the plasma membrane and nucleus. The interaction between TaSYP137 and TaVAMP723 was confirmed using the yeast two-hybrid (Y2H) system. This study offers novel insights into the involvement of SNARE proteins in the resistance of wheat against Bgt, thereby enhancing our comprehension of the role of the SNARE family in the pathways related to plant disease resistance.

Orthologous genes Pm12 and Pm21 from two wild relatives of wheat show evolutionary conservation but divergent powdery mildew resistance.

Wheat powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is a devastating disease that threatens wheat production worldwide. Pm12, which originated from Aegilops speltoides, a wild relative of wheat, confers strong resistance to powdery mildew and therefore has potential use in wheat breeding. Using susceptible mutants induced by gamma irradiation, we physically mapped and isolated Pm12 and showed it to be orthologous to Pm21 from Dasypyrum villosum, also a wild relative of wheat. The resistance function of Pm12 was validated via ethyl methanesulfonate mutagenesis, virus-induced gene silencing, and stable genetic transformation. Evolutionary analysis indicates that the Pm12/Pm21 loci in wheat species are relatively conserved but dynamic. Here, we demonstrated that the two orthologous genes, Pm12 and Pm21, possess differential resistance against the same set of Bgt isolates. Overexpression of the coiled-coil domains of both PM12 and PM21 induces cell death in Nicotiana benthamiana leaves. However, their full-length forms display different cell death-inducing activities caused by their distinct intramolecular interactions. Cloning of Pm12 will facilitate its application in wheat breeding programs. This study also gives new insight into two orthologous resistance genes, Pm12 and Pm21, which show different race specificities and intramolecular interaction patterns.

The origin and distribution of 'Kokubu'-type splice-site mutations of the MLO genes in tobacco varieties.

The Japanese domestic tobacco (Nicotiana tabacum L.) cultivar 'Kokubu' shows high powdery mildew resistance that is controlled by splice-site mutations of two MILDEW LOCUS O genes, NtMLO1 and NtMLO2. We investigated the existence of the same NtMLO1/2 splice mutations in the genomes of various tobacco varieties cultivated in Japan and other countries. In total, 14 Japanese domestic cultivars, which were mainly distributed in Kagoshima, had splice-site mutations in both NtMLO1 and NtMLO2. In addition, tobacco cultivars containing only the NtMLO1 splice-site mutation were found in various tobacco production areas in Japan, but no cultivars with only the NtMLO2 splice-site mutation were detected. Moreover, the NtMLO1 splice-site mutation was detected in native Asian, Oriental and cigar tobacco varieties. Consequently, we speculate that these powdery mildew-resistant tobacco cultivars were generated relative recently in the Kagoshima area when a spontaneous mutation occurred at the NtMLO2 splice site in a cultivar already containing the NtMLO1 splice-site mutation and that the NtMLO1 splice-site mutation occurred during the early period of tobacco seed dissemination from the Americas to Asia and Japan.

Development and Characterization of Triticum aestivum-Aegilops longissima 6Sl Recombinants Harboring a Novel Powdery Mildew Resistance Gene Pm6Sl.

Powdery mildew of wheat is a foliar disease that is spread worldwide. Cultivation of resistant varieties is the most effective, economical, and environmentally friendly strategy to curb this disease. Powdery mildew resistance genes (Pm) are the primary resources for resistance breeding, and new Pm genes are in constant demand. Previously, we identified Aegilops longissima chromosome 6Sl#3 as a carrier of powdery mildew resistance and designated the resistance gene as Pm6Sl. Here, we reported the design of 24 markers specific to 6Sl#3 on the basis of the full-length cDNA sequences of 6Sl#3 donor Ae. longissma accession TA1910, and the development of wheat-Ae. longissima 6Sl#3 introgression stocks by ph1b-induced homoeologous recombination. Further, 6Sl#3 introgression lines were identified and characterized by integration analysis of powdery mildew responses, in situ hybridization, and molecular markers and Pm6Sl was mapped to a distal interval of 42.80 Mb between markers Ael58410 and Ael57699 in the long arm of 6Sl#3. Two resistant recombinants, R43 (T6BS.6BL-6Sl#3L) and T27 (Ti6AS.6AL-6Sl#3L-6AL), contained segments harboring Pm6Sl with less than 8% of 6Sl#3 genomic length, and two markers were diagnostic for Pm6Sl. This study broadened powdery mildew resistance gene resources for wheat improvement and provided a fundamental basis for fine mapping and cloning of Pm6Sl to further understand its molecular mechanism of disease resistance.

GWAS Reveals a Novel Candidate Gene CmoAP2/ERF in Pumpkin (Cucurbita moschata) Involved in Resistance to Powdery Mildew.

Pumpkin (Cucurbita moschata Duchesne ex Poir.) is a multipurpose cash crop rich in antioxidants, minerals, and vitamins; the seeds are also a good source of quality oils. However, pumpkin is susceptible to the fungus Podosphaera xanthii, an obligate biotrophic pathogen, which usually causes powdery mildew (PM) on both sides of the leaves and reduces photosynthesis. The fruits of infected plants are often smaller than usual and unpalatable. This study identified a novel gene that involves PM resistance in pumpkins through a genome-wide association study (GWAS). The allelic variation identified in the CmoCh3G009850 gene encoding for AP2-like ethylene-responsive transcription factor (CmoAP2/ERF) was proven to be involved in PM resistance. Validation of the GWAS data revealed six single nucleotide polymorphism (SNP) variations in the CmoAP2/ERF coding sequence between the resistant (IT 274039 [PMR]) and the susceptible (IT 278592 [PMS]). A polymorphic marker (dCAPS) was developed based on the allelic diversity to differentiate these two haplotypes. Genetic analysis in the segregating population derived from PMS and PMR parents provided evidence for an incomplete dominant gene-mediated PM resistance. Further, the qRT-PCR assay validated the elevated expression of CmoAP2/ERF during PM infection in the PMR compared with PMS. These results highlighted the pivotal role of CmoAP2/ERF in conferring resistance to PM and identifies it as a valuable molecular entity for breeding resistant pumpkin cultivars.

Haploid induction in allotetraploid tobacco using DMPs mutation.

MAIN CONCLUSION: dmp1dmp2dmp3 mutants created by CRISPR/Cas9 could trigger maternal haploids in the allotetraploid model plant Nicotiana tabacum L. Double haploid (DH) technology is becoming increasingly important because it can significantly accelerate the breeding process. Haploid induction plays a fundamental role in the production of DH lines. Haploid induction has been realized and applied in diploid plants using DMP genes. However, it has yet to be elucidated whether haploid induction could be established in polyploid plants. In the current study, three homologues of the DMP genes (NtDMP1, 2, and 3) were identified in the allotetraploid plant Nicotiana tabacum, and the encoded proteins localized in the endoplasmic reticulum. Loss-of-function mutations in all three genes triggered maternal haploids with an induction rate of 1.52-1.75%. Compared with wild-type tobacco, the created haploid inducer exhibited differences in pollen vigor and seed germination rate. Furthermore, to rapidly and easily screen haploids, a visible haploid identification system was established based on a powdery mildew resistance phenotype. Findings from this study lay the foundation for the potential application of haploid inducers in allotetraploid plants such as tobacco.

Drought Stress Interacts With Powdery Mildew Infection in Tomato.

Under field conditions, plants are often exposed to more than one stress factor at the same time, and therefore need to adapt to different combinations of stresses. Crosstalk between responses to abiotic and biotic stresses is known to occur, and the interaction between stress responses can be positive or negative. We studied the interaction of drought stress and powdery mildew (PM) infection in tomatoes using near-isogenic tomato lines (NILs) carrying the Ol-1, ol-2, or Ol-4 gene that confers resistance to tomato PM caused by Oidium neolycopersici. Our study demonstrated that drought-induced growth reduction was not further reduced by powdery mildew infection. Drought stress, however, decreased fungal infection in the susceptible genotype Moneymaker (MM) with fungal biomass tending to decrease further as the drought severity increased. Drought stress did not affect PM resistance levels of resistant NIL carrying ol-2 (a mutant of the tomato susceptibility Mlo gene) and Ol-4 an NLR (nucleotide-binding site-LRR) R gene associated with a fast hypersensitivity response (HR) but tended to slightly decrease disease levels of NIL-Ol-1 (no gene characterized yet, associated with a slow HR following PM infection). At the molecular level, genes involved in abscisic acid (ABA), salicylic acid (SA), and ethylene pathways were highly induced under combined stress indicating the involvement of ABA, SA, and ethylene in the crosstalk between abiotic and biotic stress. Messenger RNA expression of the ABA-responsive dehydrin SlTAS14 was induced under drought and combined stress with the highest induction under combined stress, and resistant NIL lines showed higher expression levels than MM. The expression of SlNCED (involved in ABA synthesis) was also upregulated under drought and highly induced under combined stress. Expression levels of pathogen responsive gene SlPR1 (an indicator of the SA pathway) and SlACS (involved in ethylene synthesis) were highly induced under powdery mildew infection in MM and the Ol-1 and were induced the most under combined stress in these lines. Taken together, these findings indicate that drought stress can interact with and influence PM infection in tomatoes in a resistance type-dependent manner. The role of hormonal signaling pathways in the crosstalk between drought stress and PM infection is further discussed.

Identification and Characterization of Wheat-Aegilops comosa 7M (7A) Disomic Substitution Lines with Stripe Rust and Powdery Mildew Resistance.

Aegilops comosa (MM, 2n = 2x = 14), an important diploid species from the wheat tertiary gene pool, contains many unique genes/traits of potential use for wheat breeding, such as disease resistance. In this study, three sister lines, NAL-32, NAL-33, and NAL-34, were identified from a wheat-A. comosa distant cross using fluorescence in situ hybridization, simple sequence repeat markers, and PCR-based unique gene markers combined with single nucleotide polymorphism (SNP) array analysis. Genetically, NAL-32 contained neither an alien nor translocation chromosome, whereas NAL-33 and NAL-34 had disomic 7M (7A) substitution chromosomes but differed in the absence or presence of the 1BL/1RS translocation chromosomes, respectively. The absence of 7A in NAL-33 and NAL-34 and the unusual 1B in the latter were verified by wheat 55K SNP arrays. The two 7M (7A) substitution lines had similar levels of resistance to stripe rust and powdery mildew, but better than that of NAL-32 and their common wheat parents, suggesting that the stripe rust and powdery mildew resistance of NAL-33 and NAL-34 were derived from the 7M of A. comosa. This research provides important bridge materials that can potentially be used for transferring stripe rust and powdery mildew resistance.

A truncated CC-NB-ARC gene TaRPP13L1-3D positively regulates powdery mildew resistance in wheat via the RanGAP-WPP complex-mediated nucleocytoplasmic shuttle.

MAIN CONCLUSION: A wheat RPP13-like isoform interacting with WPP1 contributes to quantitative and/or basal resistance to powdery mildew (Blumeria graminis f. sp. tritici) by restricting the development of Bgt conidia. Plant disease resistance (R) genes confer an ability to resist infection by pathogens expressing specific avirulence genes. Recognition of Peronospora parasitica 13-like (RPP13-like) genes belong to the nucleotide-binding site and leucine-rich repeat (NBS-LRR) superfamily and play important roles in resistance to various plant diseases. Previously, we detected a TaRPP13-like gene located on chromosome 3D (TaRPP13L1-3D) in the TaSpl1 resided region, which is strongly induced by the cell death phenotype (Zhang et al. 2021). Here, we investigated the expression and functional role of TaRPP13L1-3D in wheat responding to fungal stress. TaRPP13L1-3D encoded a typical NB-ARC structure characterized by Rx-N and P-loop NTPase domains. TaRPP13L1-3D transcripts were strongly upregulated in wheat by powdery mildew (Blumeria graminis f. sp. tritici; Bgt) and stripe rust (Puccinia striiformis f. sp. tritici; Pst) infection although opposing expression patterns were observed in response to wheat-Bgt in incompatible and compatible backgrounds. Overexpression of TaRPP13L1-3D enhanced disease resistance to Bgt, accompanied by upregulation of the defense-related marker genes encoding phytoalexin-deficient4 (PAD4), thaumatin-like protein (TLP) and chitinase 8-like protein (Chi8L), while silencing of TaRPP13L1-3D disrupted the resistance to Bgt infection. Subcellular localization studies showed that TaRPP13L1-3D is located in both the plasma membrane and nucleus, while yeast-two-hybrid (Y2H) assays indicated that TaRPP13L1-3D interacts with WPP domain-containing protein 1 (TaWPP1). This indicates that TaRPP13L1-3D shuttles between the nucleus and cytoplasm membrane via a mechanism that is mediated by the RanGAP-WPP complex in nuclear pores. This insight into TaRPP13L1-3D will be useful in dissecting the mechanism of fungal resistance in wheat, and understanding the interaction between R gene expression and pathogen defense.

Construction of a genome-wide genetic linkage map and identification of quantitative trait loci for powdery mildew resistance in Gerbera daisy.

Powdery mildew (PM) is a common fungal disease in many important crops. The PM caused by Podosphaera xanthii has been the most challenging problem in commercial Gerbera (Gerbera hybrida) production globally, often leading to severe losses of crop yield and quality. A small number of PM-resistant breeding lines and cultivars have been reported in Gerbera, but the underlying genetics for PM resistance in Gerbera is largely unknown. Scarcity of genomic resources such as genetic linkage maps and molecular markers has severely hindered the effort to understand the genetic basis and locate loci controlling PM resistance in Gerbera. This study aimed to construct a genome-wide genetic linkage map, identify quantitative trait loci (QTL), and molecular markers for PM resistance in Gerbera. A segregating mapping population was developed by crossing PM-resistant and -susceptible Gerbera breeding lines, genotyped by sequencing, and phenotyped for PM resistance. A genome-wide genetic linkage map constructed with 791 single polymorphic site (SNP) markers spans 1912.30 cM across 27 linkage groups (LG) and reaches a density of 1 marker per 2.42 cM. One major consistent QTL was discovered in LG16, explaining more than 16.6% of the phenotypic variance for PM resistance. The QTL was tagged with two flanking SNP markers. The availability of this genetic linkage map will be very useful for locating and tagging QTLs for other important traits in Gerbera, and the newly discovered QTL and SNP markers will enable development of molecular markers for improving Gerbera for resistance to PM.

Production of new wheat-A. cristatum translocation lines with modified chromosome 2P coding for powdery mildew and leaf rust resistance.

Agropyron cristatum (L.) Gaertn. (2n = 28, PPPP), a relative of wheat, carries desirable genes associated with high yield, disease resistance, and stress resistance, which is an important resource for wheat genetic improvement. The long arm of A. cristatum chromosome 2P carries favorable genes conferring powdery mildew and leaf rust resistance, and two wheat-A. cristatum 2P translocation lines, 2PT3 and 2PT5, with a large segment of 2P chromatin were obtained. In this study, 2PT3 and 2PT5 translocation lines with powdery mildew and leaf rust resistance genes were used to induce translocations of different chromosomal sizes via ionizing radiation. According to cytological characterization, 10 of those plants were new wheat-A. cristatum 2P small-chromosome segment translocation lines with reduced 2P chromatin, and 6 plants represented introgression lines without visible 2P chromosomal fragments. Moreover, four lines were resistant to both powdery mildew and leaf rust, while two lines were resistant only to leaf rust.

Characterization, Identification and Evaluation of Wheat-Aegilops sharonensis Chromosome Derivatives.

Aegilops sharonensis, a wild relative of wheat, harbors diverse disease and insect resistance genes, making it a potentially excellent gene source for wheat improvement. In this study, we characterized and evaluated six wheat-A. sharonensis derivatives, which included three disomic additions, one disomic substitution + monotelosomic addition and two disomic substitution + disomic additions. A total of 51 PLUG markers were developed and used to allocate the A. sharonensis chromosomes in each of the six derivatives to Triticeae homoeologous groups. A set of cytogenetic markers specific for A. sharonensis chromosomes was established based on FISH using oligonucleotides as probes. Molecular cytogenetic marker analysis confirmed that these lines were a CS-A. sharonensis 2Ssh disomic addition, a 4Ssh disomic addition, a 4Ssh (4D) substitution + 5SshL monotelosomic addition, a 6Ssh disomic addition, a 4Ssh (4D) substitution + 6Ssh disomic addition and a 4Ssh (4D) substitution + 7Ssh disomic addition line, respectively. Disease resistance investigations showed that chromosome 7Ssh of A. sharonensis might harbor a new powdery mildew resistance gene, and therefore it has potential for use as resistance source for wheat breeding.

Grape Transcriptome Response to Powdery Mildew Infection: Comparative Transcriptome Profiling of Chinese Wild Grapes Provides Insights Into Powdery Mildew Resistance.

Erysiphe necator, the fungal pathogen of grape powdery mildew disease, poses a great threat to the grape market and the wine industry. To better understand the molecular basis of grape responses to E. necator, we performed comparative transcriptome profiling on two Chinese wild grape accessions with varying degrees of resistance to E. necator. At 6-, 24-, and 96-h postinoculation of E. necator, 2,856, 2,678, and 1,542 differentially expressed genes (DEGs) were identified in the susceptible accession Vitis pseudoreticulata 'Hunan-1', and at those same time points, 1,921, 2,498, and 3,249 DEGs, respectively, were identified in the resistant accession V. quinquangularis 'Shang-24'. 'Hunan-1' had a substantially larger fraction of down-regulated genes than 'Shang-24' at every infection stage. Analysis of DEGs revealed that up-regulated genes were mostly associated with defense response and disease resistance-related metabolite biosynthesis, and such signaling genes were significantly suppressed in 'Hunan-1'. Interestingly, fatty acid biosynthesis- and elongation-related genes were suppressed by the fungus in the 'Shang-24' accession but somehow induced in the 'Hunan-1' accession, consistent with the concept that E. necator is likely to be a fatty acid auxotroph that requires lipids from the host. Moreover, genes involved in biosynthesis and signaling of phytohormones, such as jasmonic acid and cytokinin, as well as genes encoding protein kinases and nucleotide-binding domain leucine-rich repeat proteins, differentially responded to E. necator in the two wild grapes. The variation of gene regulation associated with nutrient uptake by the fungus and with signaling transduction and pathogen recognition suggests a multilayered regulatory network that works in concert to assist in the establishment of fungal pathogen infections.

Development of Novel Wheat-Aegilops longissima 3S1 Translocations Conferring Powdery Mildew Resistance and Specific Molecular Markers for Chromosome 3S1.

Powdery mildew of wheat, caused by Blumeria graminis f. sp. tritici, is a destructive disease of common wheat. Cultivation of resistant varieties is the most cost-effective disease management strategy. Previous studies reported that chromosome 3Sl#2 present in Chinese Spring (CS)-Aegilops longissima 3Sl#2(3B) disomic substitution line TA3575 conferred resistance to powdery mildew. In this study, we further located the powdery mildew resistance gene(s) to the short arm of chromosome 3Sl#2 (3Sl#2S) by evaluating for B. graminis f. sp. tritici resistance of newly developed CS-Ae. longissima 3Sl#2 translocation lines. Meanwhile, TA7545, a previously designated CS-Ae. longissima 3Sl#3 disomic addition line, was reidentified as an isochromosome 3Sl#3S addition line and evaluated to confer resistance to powdery mildew, thus locating the resistance gene(s) to the short arm of chromosome 3Sl#3 (3Sl#3S). Based on transcriptome sequences of TA3575, 10 novel chromosome 3SlS-specific markers were developed, of which 5 could be used to distinguish between 3Sl#2S and 3Sl#3S derived from Ae. longissima accessions TL20 and TA1910 (TAM4) and the remaining 5 could identify both 3Sl#2S and 3Sl#3S. Also, CL897, one of five markers specific to both 3Sl#2S and 3Sl#3S, could be used to detect Pm13 located at chromosome 3Sl#1S from Ae. longissima accession TL01 in diverse wheat genetic backgrounds. The powdery mildew resistance genes on chromosomes 3Sl#2S and 3Sl#3S, the CS-Ae. longissima 3Sl#2 translocation lines, and the 3SlS-specific markers developed in this study will facilitate the transfer of B. graminis f. sp. tritici resistance genes into common wheat and provide new germplasm resources for powdery mildew resistance breeding.

Characterization of lncRNAs and mRNAs Involved in Powdery Mildew Resistance in Cucumber.

Powdery mildew (PM) is a severe fungal disease of cucumber worldwide. Identification of genetic factors resistant to PM is of great importance for marker-assisted breeding to ensure cucumber production. Long noncoding RNAs (lncRNAs) and microRNAs (miRNAs) have been shown to play important roles in plant development and immunity; however, whether they have a role in PM response in cucurbit crops remains unknown. We performed strand-specific RNA sequencing and miRNA sequencing using RNA from cucumber leaves of two near-isogenic lines (NILs), S1003 and NIL (Pm5.1) infected with PM, and systematically characterized the profiles of cucumber lncRNAs and messenger RNA (mRNAs) responsive to PM. In total, we identified 12,903 lncRNAs and 25,598 mRNAs responsive to PM. Differential expression (DE) analysis showed that 119 lncRNAs and 136 mRNAs correlated with PM resistance. Functional analysis of these DE lncRNAs and DE mRNAs revealed that they are significantly associated with phenylpropanoid biosynthesis, phenylalanine metabolism, ubiquinone and other terpenoid-quinone biosynthesis, and endocytosis. Particularly, two lncRNAs, LNC_006805 and LNC_012667, might play important roles in PM resistance. In addition, we also predicted mature miRNAs and competing endogenous RNA (ceRNA) networks of lncRNA-miRNA-mRNA involved in PM resistance. A total of 49 DE lncRNAs could potentially act as target mimics for 106 miRNAs. Taken together, our results provide an abundant resource for further exploration of cucumber lncRNAs, mRNAs, miRNAs, and ceRNAs in PM resistance, and will facilitate the molecular breeding for PM-resistant varieties to control this severe disease in cucumber.