Phytophthora sojae effector PsAvh113 associates with the soybean transcription factor GmDPB to inhibit catalase-mediated immunity.

Phytophthora species are the most destructive plant pathogens worldwide and the main threat to agricultural and natural ecosystems; however, their pathogenic mechanism remains largely unknown. Here, we show that Avh113 effector is required for the virulence of Phytophthora sojae and is important for development of Phytophthora root and stem rot (PRSR) in soybean (Glycine max). Ectopic expression of PsAvh113 enhanced viral and Phytophthora infection in Nicotiana benthamiana. PsAvh113 directly associated with the soybean transcription factor GmDPB, inducing its degradation by the 26S proteasome. The internal repeat 2 (IR2) motif of PsAvh113 was important for its virulence and interaction with GmDPB, while silencing and overexpression of GmDPB in soybean hairy roots altered the resistance to P. sojae. Upon binding to GmDPB, PsAvh113 decreased the transcription of the downstream gene GmCAT1, which acts as a positive regulator of plant immunity. Furthermore, we revealed that PsAvh113 suppressed the GmCAT1-induced cell death by associating with GmDPB, thereby enhancing plant susceptibility to Phytophthora. Together, our findings reveal a vital role of PsAvh113 in inducing PRSR in soybean and offer a novel insight into the interplay between defence and counter-defence during the P. sojae infection of soybean.

Genome-Wide Identification and Characterization of Wheat 14-3-3 Genes Unravels the Role of TaGRF6-A in Salt Stress Tolerance by Binding MYB Transcription Factor.

14-3-3 proteins are a large multigenic family of general regulatory factors (GRF) ubiquitously found in eukaryotes and play vital roles in the regulation of plant growth, development, and response to stress stimuli. However, so far, no comprehensive investigation has been performed in the hexaploid wheat. In the present study, A total of 17 potential 14-3-3 gene family members were identified from the Chinese Spring whole-genome sequencing database. The phylogenetic comparison with six 14-3-3 families revealed that the majority of wheat 14-3-3 genes might have evolved as an independent branch and grouped into ε and non-ε group using the phylogenetic comparison. Analysis of gene structure and motif indicated that 14-3-3 protein family members have relatively conserved exon/intron arrangement and motif composition. Physical mapping showed that wheat 14-3-3 genes are mainly distributed on chromosomes 2, 3, 4, and 7. Moreover, most 14-3-3 members in wheat exhibited significantly down-regulated expression in response to alkaline stress. VIGS assay and protein-protein interaction analysis further confirmed that TaGRF6-A positively regulated slat stress tolerance by interacting with a MYB transcription factor, TaMYB64. Taken together, our findings provide fundamental information on the involvement of the wheat 14-3-3 family in salt stress and further investigating their molecular mechanism.

Novel Wx alleles generated by base editing for improvement of rice grain quality.

Amylose content (AC), which is regulated by the Waxy (Wx) gene, is a major indicator of eating and cooking quality (ECQ) in rice (Oryza sativa). Thus far, only a limited number of mutations in the N-terminal domain of Wx were found to have a major impact on the AC of rice grains and no mutations with such effects were reported for other regions of the Wx protein. Here, nucleotide substitutions in the middle region of Wx were generated by adenine and cytosine base editors. The nucleotide substitutions led to changes in 15 amino acid residues of Wx, and a series of novel Wx alleles with ACs of 0.3%-29.43% (wild type with AC of 19.87%) were obtained. Importantly, the waxyabe2 allele showed a "soft rice" AC, improved ECQ, favorable appearance, and no undesirable agronomic traits. The transgenes were removed from the waxyabe2 progeny, generating a promising breeding material for improving rice grain quality.

A stripe rust effector Pst18363 targets and stabilises TaNUDX23 that promotes stripe rust disease.

Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), poses a tremendous threat to the production of wheat worldwide. The molecular mechanisms of Pst effectors that regulate wheat immunity are poorly understood. In this study, we identified an effector Pst18363 from Pst that suppresses plant cell death in Nicotiana benthamiana and in wheat. Knocking down Pst18363 expression by virus-mediated host-induced gene silencing significantly decreased the number of rust pustules, indicating that Pst18363 functions as an important pathogenicity factor in Pst. Pst18363 was proven to interact with wheat Nudix hydrolase 23 TaNUDX23. In wheat, silencing of TaNUDX23 by virus-induced gene silencing increased reactive oxygen species (ROS) accumulation induced by the avirulent Pst race CYR23, whereas overexpression of TaNUDX23 suppressed ROS accumulation induced by flg22 in Arabidopsis. In addition, TaNUDX23 suppressed Pst candidate effector Pst322-trigged cell death by decreasing ROS accumulation in N. benthamiana. Knocking down of TaNUDX23 expression attenuated Pst infection, indicating that TaNUDX23 is a negative regulator of defence. In N. benthamiana, Pst18363 stabilises TaNUDX23. Overall, our data suggest that Pst18363 stabilises TaNUDX23, which suppresses ROS accumulation to facilitate Pst infection.

A novel MADS-box transcription factor PstMCM1-1 is responsible for full virulence of Puccinia striiformis f. sp. tritici.

In many eukaryotes, transcription factor MCM1 gene plays crucial roles in regulating mating processes and pathogenesis by interacting with other co-factors. However, little is known about the role of MCM1 in rust fungi. Here, we identified two MCM1 orthologs, PstMCM1-1 and PstMCM1-2, in the stripe rust pathogen Puccinia striiformis f. sp. tritici (Pst). Sequence analysis indicated that both PstMCM1-1 and PstMCM1-2 contain conserved MADS domains and that PstMCM1-1 belongs to a group of SRF-like proteins that are evolutionarily specific to rust fungi. Yeast two-hybrid assays indicated that PstMCM1-1 interacts with transcription factors PstSTE12 and PstbE1. PstMCM1-1 was found to be highly induced during early infection stages in wheat and during pycniospore formation on the alternate host barberry (Berberis shensiana). PstMCM1-1 could complement the lethal phenotype and mating defects in a mcm1 mutant of Saccharomyces cerevisiae. In addition, it partially complemented the defects in appressorium formation and plant infection in a Magnaporthe oryzae Momcm1 mutant. Knock down of PstMCM1-1 resulted in a significant reduction of hyphal extension and haustorium formation and the virulence of Pst on wheat. Our results suggest that PstMCM1-1 plays important roles in the regulation of mating and pathogenesis of Pst most likely by interacting with co-factors.

Host-induced gene silencing of an important pathogenicity factor PsCPK1 in Puccinia striiformis f. sp. tritici enhances resistance of wheat to stripe rust.

Rust fungi are devastating plant pathogens and cause a large economic impact on wheat production worldwide. To overcome this rapid loss of resistance in varieties, we generated stable transgenic wheat plants expressing short interfering RNAs (siRNAs) targeting potentially vital genes of Puccinia striiformis f. sp. tritici (Pst). Protein kinase A (PKA) has been proved to play important roles in regulating the virulence of phytopathogenic fungi. PsCPK1, a PKA catalytic subunit gene from Pst, is highly induced at the early infection stage of Pst. The instantaneous silencing of PsCPK1 by barley stripe mosaic virus (BSMV)-mediated host-induced gene silencing (HIGS) results in a significant reduction in the length of infection hyphae and disease phenotype. These results indicate that PsCPK1 is an important pathogenicity factor by regulating Pst growth and development. Two transgenic lines expressing the RNA interference (RNAi) construct in a normally susceptible wheat cultivar displayed high levels of stable and consistent resistance to Pst throughout the T3 to T4 generations. The presence of the interfering RNAs in transgenic wheat plants was confirmed by northern blotting, and these RNAs were found to efficiently down-regulate PsCPK1 expression in wheat. This study addresses important aspects for the development of fungal-derived resistance through the expression of silencing constructs in host plants as a powerful strategy to control cereal rust diseases.

Host-Induced Gene Silencing of the MAPKK Gene PsFUZ7 Confers Stable Resistance to Wheat Stripe Rust.

RNA interference (RNAi) is a powerful genetic tool to accelerate research in plant biotechnology and control biotic stresses by manipulating target gene expression. However, the potential of RNAi in wheat to efficiently and durably control the devastating stripe rust fungus Puccinia striiformis f. sp. tritici (Pst) remained largely under explored so far. To address this issue, we generated transgenic wheat (Triticum aestivum) lines expressing dsRNA targeting PsFUZ7 transcripts of Pst We analyzed expression of PsFUZ7 and related genes, and resistance traits of the transgenic wheat lines. We show that PsFUZ7 is an important pathogenicity factor that regulates infection and development of Pst A PsFUZ7 RNAi construct stably expressed in two independent transgenic wheat lines confers strong resistance to PstPst hyphal development is strongly restricted, and necrosis of plant cells in resistance responses was significantly induced. We conclude that trafficking of RNA molecules from wheat plants to Pst may lead to a complex molecular dialogue between wheat and the rust pathogen. Moreover, we confirm the RNAi-based crop protection approaches can be used, to our knowledge, as a novel control strategy against rust pathogens in wheat.

[Function of a calcium-dependent protein kinase gene Pscamk in Puccinia striiformis f. sp. tritici].

OBJECTIVE: To clone calcium-dependent protein kinase gene (camk) from Puccinia striiformis f. sp. tritici (Pst) and analyze its function. METHODS: The cDNA full-length of Pscamk was isolated by using reverse transcriptional-PCR (RT-PCR), and gene expression profile at different morphological stages was analyzed via quantitative real-time--PCR (qRT-PCR). Pst urediospores were treated with CaMK suppressor KN-93 and germination rate was investigated. RESULTS: A gene cDNA full-length with 1 620 bp was obtained and designated as Pscamk. qRT-PCR analysis showed Pscamk expression was highly induced in the early stages of Pst infection and reached the maximum at 6 h post inoculation (hpi) as 20.74-fold as that in the control (0 hpi). With increasing of the concentration of CaMK suppressor KN-93, germination rate of Pst urediospores was gradually decreased. The germination rate was reduced to 8.02%, only 12% of the control, under 1.4 µmol/L KN-93 treatment at 10 h after incubation at 9 degrees C. CONCLUSION: Pscamk might play a role in germination and germ tube elongation of Pst urediospores. This study provides a basis for exploring pathogenesis of calcium signaling pathway during Pst infection.

Phytophthora sojae boosts host trehalose accumulation to acquire carbon and initiate infection.

Successful infection by pathogenic microbes requires effective acquisition of nutrients from their hosts. Root and stem rot caused by Phytophthora sojae is one of the most important diseases of soybean (Glycine max). However, the specific form and regulatory mechanisms of carbon acquired by P. sojae during infection remain unknown. In the present study, we show that P. sojae boosts trehalose biosynthesis in soybean through the virulence activity of an effector PsAvh413. PsAvh413 interacts with soybean trehalose-6-phosphate synthase 6 (GmTPS6) and increases its enzymatic activity to promote trehalose accumulation. P. sojae directly acquires trehalose from the host and exploits it as a carbon source to support primary infection and development in plant tissue. Importantly, GmTPS6 overexpression promoted P. sojae infection, whereas its knockdown inhibited the disease, suggesting that trehalose biosynthesis is a susceptibility factor that can be engineered to manage root and stem rot in soybean.

High-Throughput Sequencing-Based Identification of Arabidopsis miRNAs Induced by Phytophthora capsici Infection.

MicroRNAs (miRNAs) are a group of small non-coding endogenous RNAs. In plants, miRNAs play vital functions in regulating growth, development, and stress response. However, the role of miRNAs in Arabidopsis-Phytophthora capsici (P. capsici) model pathosystem is poorly understood. Here, we used a high-throughput sequencing approach to identify pathogen-responsive miRNAs using 15 small RNA (sRNA) libraries prepared from Arabidopsis thaliana leaves collected at 0, 3, 6, 12, and 24 h post-inoculation with P. capsici. A total of 293 known miRNAs and 6 potential novel sRNAs (miRNAs or siRNAs) were identified, of which 33 miRNAs were differentially expressed at four different infection stages. To verify the reliability of the sRNA-seq results, we investigated the expression of five sRNAs upregulated throughout the four infection stages and their potential target genes using northern blot analysis and/or stem-loop quantitative real-time polymerase chain reaction (qRT-PCR). Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses revealed that the potential target genes of the differentially expressed miRNAs, both conserved and novel, were enriched in pathways such as starch and sugar metabolism, spliceosome, and plant-pathogen interaction, indicating that the splicing machinery and pathogenesis-related (PR) proteins play important roles in the response to P. capsici infection. Taken together, these results provide novel insights into the molecular mechanisms of pathogenesis by P. capsici. Additionally, these results will serve as a strong foundation for further in-depth analysis of miRNAs involved in the resistance to Phytophthora species in other crops.

Genome-Wide Mining of Wheat DUF966 Gene Family Provides New Insights Into Salt Stress Responses.

Domain of unknown function (DUF) proteins constitute a great deal of families of functionally uncharacterized proteins in eukaryotes. The DUF966 gene family is found in monocotyledons, dicotyledons, mosses, and other species. However, little is known about the functions of DUF966 genes in wheat (Triticum aestivum L.). In this study, we identified and characterized the TaDUF966 gene family members in wheat by in silico analysis. A total of 28 TaDUF966 proteins were identified in wheat. Phylogenetic analysis divided these proteins into two groups (Groups I and II). Proteins in each group showed a highly conserved DUF966 domain and conserved motif distribution, implying their functional conservation. Analysis of gene expression profiling data showed that some TaDUF966 genes were induced by salt stress. We further confirmed the role of TaDUF966-9B in salt stress using virus induced gene silencing (VIGS) assay. Compared with the empty vector control, the TaDUF966-9B knockdown plants exhibited severe leaf curling at 10 days post-inoculation with BSMV under salt stress, suggesting that TaDUF966 genes play a vital role in salt stress tolerance in wheat. Taken together, these results expand our knowledge of the evolution of the DUF966 gene family in wheat and promote the potential application of these genes in wheat genetic improvement.

Silencing PsKPP4, a MAP kinase kinase kinase gene, reduces pathogenicity of the stripe rust fungus.

Many obligately parasitic pathogens absorb nutrients from host plants via specialized infection structures, called haustoria and infection hyphae, to further colonization and growth in the host plant. In the wheat (Triticum aestivum) stripe rust fungus, Puccinia striiformis f. sp. tritici (Pst), the mitogen-activated protein kinase kinase (MAPKK) PsFUZ7 is involved in the regulation of haustorium formation and invasive growth. Here, we functionally characterized PsKPP4 of Pst, which is homologous to the yeast MAPKKK STE11. Similar to the silencing of PsFUZ7, the knockdown of PsKPP4 was detected in the vegetative hyphae and haustoria, resulting in the reduced pathogenicity of Pst. Pst urediniospores treated with the STE11 MAPKKK activation inhibitor produced deformed germ tubes. In addition, overexpression of PsKPP4 in fission yeast resulted in the production of fusiform cells and increased tolerance of yeast cells to oxidative stress. The transformation of PsKPP4 into the mst11 mutant of Magnaporthe oryzae partially restored mst11 function. The PsKPP4 protein contains a sterile alpha motif (SAM), Ras association (RA) and kinase domains, similar to its homologues in other fungi. Yeast two-hybrid assays revealed that the SAM domain is essential for the interaction between PsKPP4 and PsUBC2, a homologue of Ustilago maydis UBC2, known to interact with KPP4, which is associated with the regulation of the Fus3 cascade. Host-induced gene silencing of PsUBC2 reduced the pathogenicity of Pst slightly, indicating that PsUBC2 also plays a minor role in the regulation of the infection pathway of Pst. These observations indicate that PsKPP4, interacting with PsUBC2, may play an important role in the regulation of infection-related morphogenesis in Pst.

The transcription factor PstSTE12 is required for virulence of Puccinia striiformis f. sp. tritici.

Puccinia striiformis f. sp. tritici (Pst) is an obligate biotrophic fungus that causes extensive damage in wheat. The pathogen is now known to be a heteroecious fungus with an intricate life cycle containing sexual and asexual stages. Orthologues of the STE12 transcription factor that regulate mating and filamentation in Saccharomyces cerevisiae, as well as virulence in other fungi, have been extensively described. Because reliable transformation and gene disruption methods are lacking for Pst, knowledge about the function of its STE12 orthologue is limited. In this study, we identified a putative orthologue of STE12 from Pst in haustoria-enriched transcripts and designated it as PstSTE12. The gene encodes a protein of 879 amino acids containing three helices in the homeodomain, conserved phenylalanine and tryptophan sites, and two C2 /H2 -Zn2+ finger domains. Real-time reverse transcription-polymerase chain reaction (RT-PCR) analyses revealed that the expression of PstSTE12 was highly induced during the early infection stages and peaked during haustorium formation and the pycniospore stage in the aecial host barberry. Subcellular localization assays indicated that PstSTE12 is localized in the nucleus and functions as a transcriptional activator. Yeast one-hybrid assays revealed that PstSTE12 exhibits transcriptional activity, and that its C-terminus is necessary for the activation of transcription. PstSTE12 complemented the mating defect in an α ste12 mutant of S. cerevisiae. In addition, it partially complemented the defects of the Magnaporthe oryzae mst12 mutant in plant infection. Knocking down PstSTE12 via host-induced gene silencing (HIGS) mediated by Barley stripe mosaic virus (BSMV) resulted in a substantial reduction in the growth and spread of hyphae in Pst and weakened the virulence of Pst on wheat. Our results suggest that PstSTE12 probably acts at an intersection participating in the invasion and mating processes of Pst, and provide new insights into the comprehension of the variation of virulence in cereal rust fungi.

Genetic diversity and population structure of cucumber (Cucumis sativus L.).

Knowing the extent and structure of genetic variation in germplasm collections is essential for the conservation and utilization of biodiversity in cultivated plants. Cucumber is the fourth most important vegetable crop worldwide and is a model system for other Cucurbitaceae, a family that also includes melon, watermelon, pumpkin and squash. Previous isozyme studies revealed a low genetic diversity in cucumber, but detailed insights into the crop's genetic structure and diversity are largely missing. We have fingerprinted 3,342 accessions from the Chinese, Dutch and U.S. cucumber collections with 23 highly polymorphic Simple Sequence Repeat (SSR) markers evenly distributed in the genome. The data reveal three distinct populations, largely corresponding to three geographic regions. Population 1 corresponds to germplasm from China, except for the unique semi-wild landraces found in Xishuangbanna in Southwest China and East Asia; population 2 to Europe, America, and Central and West Asia; and population 3 to India and Xishuangbanna. Admixtures were also detected, reflecting hybridization and migration events between the populations. The genetic background of the Indian germplasm is heterogeneous, indicating that the Indian cucumbers maintain a large proportion of the genetic diversity and that only a small fraction was introduced to other parts of the world. Subsequently, we defined a core collection consisting of 115 accessions and capturing over 77% of the SSR alleles. Insight into the genetic structure of cucumber will help developing appropriate conservation strategies and provides a basis for population-level genome sequencing in cucumber.