The genome of the rice variety LTH provides insight into its universal susceptibility mechanism to worldwide rice blast fungal strains

Inhibitor of cardiolipin biosynthesis-related enzyme MoGep4 confers broad-spectrum anti-fungal activity

Plant pathogens cause devastating diseases, leading to serious losses to agriculture. Mechanistic understanding of pathogenesis of plant pathogens lays the foundation for the development of fungicides for disease control. Mitophagy, a specific form of autophagy, is important for fungal virulence. The role of cardiolipin, mitochondrial signature phospholipid, in mitophagy and pathogenesis is largely unknown in plant pathogenic fungi. The functions of enzymes involved in cardiolipin biosynthesis and relevant inhibitors were assessed using a set of assays, including genetic deletion, plant infection, lipidomics, chemical-protein interaction, chemical inhibition, and field trials. Our results showed that the cardiolipin biosynthesis-related gene MoGEP4 of the rice blast fungus Magnaporthe oryzae regulates growth, conidiation, cardiolipin biosynthesis, and virulence. Mechanistically, MoGep4 regulated mitophagy and Mps1-MAPK phosphorylation, which are required for virulence. Chemical alexidine dihydrochloride (AXD) inhibited the enzyme activity of MoGep4, cardiolipin biosynthesis and mitophagy. Importantly, AXD efficiently inhibited the growth of 10 plant pathogens and controlled rice blast and Fusarium head blight in the field. Our study demonstrated that MoGep4 regulates mitophagy, Mps1 phosphorylation and pathogenesis in M. oryzae. In addition, we found that the MoGep4 inhibitor, AXD, displays broad-spectrum antifungal activity and is a promising candidate for fungicide development.

Full-length transcriptome characterization and analysis of Carrizo Citrange and molecular insights into pathogen defense

Citrus huanglongbing (HLB) is a major challenge that impacts the flourishing of the citrus industry. Therefore, analyzing the genomic information of HLB-resistant or tolerant citrus resources is crucial for breeding HLB-resistant citrus varieties. The Carrizo citrange, a hybrid of Citrus sinensis and Poncirus trifoliata, plays a pivotal role in citrus cultivation. However, its genetic explorations are difficult due to the absence of a reference genome or full-length transcriptome. In order to enhance our understanding of the genetic information of citrange, we conducted a full-length transcriptomic sequencing of multiple tissues from the Carrizo citrange using the PacBio Sequel II platform. Moreover, we performed gene ontology (GO) annotation, gene functional annotation, simple sequence repeats (SSR) types analysis, as well as identification of lncRNAs, alternative splicing events, and analysis of pathogen defense-related genes. Results showed that a total of 43,452 isoforms were generated, with 43,307 of them being annotated. GO annotation indicated the involvement of these isoforms in various biological processes, cellular components, and molecular functions. The coding sequence length of the isoforms ranged from 1,000 to 4,000 base pairs (bp). Moreover, we have discovered 54 varieties of transcription factors and regulators, along with 16 classifications of genes associated with resistance. Among all types of SSRs, trimer type SSRs were the most abundant. 130 lncRNAs were predicted to be highly reliable in the isoforms of the Carrizo citrange, with alternative splicing events identified, and the most frequent being retained intron. The analysis of gene family expansion and contraction revealed a significant increase in pathogen defense-related genes within the Carrizo citrange. The results of this study will be of great value for future investigations into gene function in citrange and for expanding the genetic pool for breeding citrus varieties resistant or tolerant to HLB.

Genomic and transcriptomic analyses of the elite rice variety Huizhan provide insight into disease resistance and heat tolerance

The indica rice variety Huizhan shows elite traits of disease resistance and heat tolerance. However, the underlying genetic basis of these traits is not fully understood due to limited genomic resources. Here, we used Nanopore long-read and next-generation sequencing technologies to generate a chromosome-scale genome assembly of Huizhan. Comparative genomics analysis uncovered a large chromosomal inversion and expanded gene families that are associated with plant growth, development and stress responses. Functional rice blast resistance genes, including Pi2, Pib and Ptr, and bacterial blight resistance gene Xa27, contribute to disease resistance of Huizhan. Furthermore, integrated genomics and transcriptomics analyses showed that OsHIRP1, OsbZIP60, the SOD gene family, and various transcription factors are involved in heat tolerance of Huizhan. The high-quality genome assembly and comparative genomics results presented in this study facilitate the use of Huizhan as an elite parental line in developing rice varieties adapted to disease pressure and climate challenges.

Phytoalexin sakuranetin attenuates endocytosis and enhances resistance to rice blast

Phytoalexin sakuranetin functions in resistance against rice blast. However, the mechanisms underlying the effects of sakuranetin remains elusive. Here, we report that rice lines expressing resistance (R) genes were found to contain high levels of sakuranetin, which correlates with attenuated endocytic trafficking of plasma membrane (PM) proteins. Exogenous and endogenous sakuranetin attenuates the endocytosis of various PM proteins and the fungal effector PWL2. Moreover, accumulation of the avirulence protein AvrCO39, resulting from uptake into rice cells by Magnaporthe oryzae, was reduced following treatment with sakuranetin. Pharmacological manipulation of clathrin-mediated endocytic (CME) suggests that this pathway is targeted by sakuranetin. Indeed, attenuation of CME by sakuranetin is sufficient to convey resistance against rice blast. Our data reveals a mechanism of rice against M. oryzae by increasing sakuranetin levels and repressing the CME of pathogen effectors, which is distinct from the action of many R genes that mainly function by modulating transcription.

Characterization of Blast Resistance in a Diverse Rice Panel from Sub-Saharan Africa

There is a recent unparalleled increase in demand for rice in sub-Saharan Africa, yet its production is affected by blast disease. Characterization of blast resistance in adapted African rice cultivars can provide important information to guide growers and rice breeders. We used molecular markers for known blast resistance genes (Pi genes; n = 21) to group African rice genotypes (n = 240) into similarity clusters. We then used greenhouse-based assays to challenge representative rice genotypes (n = 56) with African isolates (n = 8) of Magnaporthe oryzae which varied in virulence and genetic lineage. The markers grouped rice cultivars into five blast resistance clusters (BRC) which differed in foliar disease severity. Using stepwise regression, we found that the Pi genes associated with reduced blast severity were Pi50 and Pi65, whereas Pik-p, Piz-t, and Pik were associated with increased susceptibility. All rice genotypes in the most resistant cluster, BRC 4, possessed Pi50 and Pi65, the only genes that were significantly associated with reduced foliar blast severity. Cultivar IRAT109, which contains Piz-t, was resistant against seven African M. oryzae isolates, whereas ARICA 17 was susceptible to eight isolates. The popular Basmati 217 and Basmati 370 were among the most susceptible genotypes. These findings indicate that most tested genes were not effective against African blast pathogen collections. Pyramiding genes in the Pi2/9 multifamily blast resistance cluster on chromosome 6 and Pi65 on chromosome 11 could confer broad-spectrum resistance capabilities. To gain further insights into genomic regions associated with blast resistance, gene mapping could be conducted with resident blast pathogen collections. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Salicylic acid inhibits rice endocytic protein trafficking mediated by OsPIN3t and clathrin to affect root growth

Salicylic acid (SA) plays important roles in different aspects of plant development, including root growth, where auxin is also a major player by means of its asymmetric distribution. However, the mechanism underlying the effect of SA on the development of rice roots remains poorly understood. Here, we show that SA inhibits rice root growth by interfering with auxin transport associated with the OsPIN3t- and clathrin-mediated gene regulatory network (GRN). SA inhibits root growth as well as Brefeldin A-sensitive trafficking through a non-canonical SA signaling mechanism. Transcriptome analysis of rice seedlings treated with SA revealed that the OsPIN3t auxin transporter is at the center of a GRN involving the coat protein clathrin. The root growth and endocytic trafficking in both the pin3t and clathrin heavy chain mutants were SA insensitivity. SA inhibitory effect on the endocytosis of OsPIN3t was dependent on clathrin; however, the root growth and endocytic trafficking mediated by tyrphostin A23 (TyrA23) were independent of the pin3t mutant under SA treatment. These data reveal that SA affects rice root growth through the convergence of transcriptional and non-SA signaling mechanisms involving OsPIN3t-mediated auxin transport and clathrin-mediated trafficking as key components.

Emergence of Rice Blast AVR-Pi9 Resistance Breaking Haplotypes in Yunnan Province, China

The rice blast disease (caused by Magnaporthe oryzae) is a devastating disease in China. Understanding the molecular mechanisms of interaction for the cognate avirulence (AVR) gene with host resistance (R) genes, as well as their genetic evolution is essential for sustainable rice production. In the present study, we conducted a high-throughput nucleotide sequence polymorphism analysis of the AVR-Pi9 gene that was amplified from the rice-growing regions of the Yunnan Province in China. We detected the presence of seven novel haplotypes from 326 rice samples. In addition, the sequences of AVR-Pi9 were also obtained from two non-rice hosts, Eleusine coracana and Eleusine indica. The sequence analysis revealed the insertions and deletions in the coding and non-coding regions of the gene. The pathogenicity experiments of these haplotypes on previously characterized monogenic lines showed that the newly identified haplotypes are virulent in nature. The breakdown of resistance was attributed to the development of new haplotypes. Our results suggest that the mutation in the AVR-Pi9 gene is an alarming situation in the Yunnan province and thus needs attention.

Genome editing of a rice CDP-DAG synthase confers multipathogen resistance

The discovery and application of genome editing introduced a new era of plant breeding by giving researchers efficient tools for the precise engineering of crop genomes1. Here we demonstrate the power of genome editing for engineering broad-spectrum disease resistance in rice (Oryza sativa). We first isolated a lesion mimic mutant (LMM) from a mutagenized rice population. We then demonstrated that a 29-base-pair deletion in a gene we named RESISTANCE TO BLAST1 (RBL1) caused broad-spectrum disease resistance and showed that this mutation caused an approximately 20-fold reduction in yield. RBL1 encodes a cytidine diphosphate diacylglycerol synthase that is required for phospholipid biosynthesis2. Mutation of RBL1 results in reduced levels of phosphatidylinositol and its derivative phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2). In rice, PtdIns(4,5)P2 is enriched in cellular structures that are specifically associated with effector secretion and fungal infection, suggesting that it has a role as a disease-susceptibility factor3. By using targeted genome editing, we obtained an allele of RBL1, named RBL1Δ12, which confers broad-spectrum disease resistance but does not decrease yield in a model rice variety, as assessed in small-scale field trials. Our study has demonstrated the benefits of editing an LMM gene, a strategy relevant to diverse LMM genes and crops.

A large-scale assessment of the quality of plant genome assemblies using the LTR assembly index

Recent advances in genome sequencing have led to an increase in the number of sequenced genomes. However, the presence of repetitive sequences complicates the assembly of plant genomes. The LTR assembly index (LAI) has recently been widely used to assess the quality of genome assembly, as a higher LAI is associated with a higher quality of assembly. Here, we assessed the quality of assembled genomes of 1664 plant and algal genomes using LAI and reported the results as data repository called PlantLAI (https://bioinformatics.um6p.ma/PlantLAI). A number of 55 117 586 pseudomolecules/scaffolds with a total length of 988.11 gigabase-pairs were examined using the LAI workflow. A total of 46 583 551 accurate LTR-RTs were discovered, including 2 263 188 Copia, 2 933 052 Gypsy, and 1 387 311 unknown superfamilies. Consequently, only 1136 plant genomes are suitable for LAI calculation, with values ranging from 0 to 31.59. Based on the quality classification system, 476 diploid genomes were classified as draft, 472 as reference, and 135 as gold genomes. We also provide a free webtool to calculate the LAI of newly assembled genomes and the ability to save the result in the repository. The data repository is designed to fill in the gaps in the reported LAI of existing genomes, while the webtool is designed to help researchers calculate the LAI of their newly sequenced genomes.

Doxorubicin inhibits phosphatidylserine decarboxylase and confers broad-spectrum antifungal activity

As phospholipids of cell membranes, phosphatidylethanolamine (PE) and phosphatidylserine (PS) play crucial roles in glycerophospholipid metabolism. Broadly, some phospholipid biosynthesis enzymes serve as potential fungicide targets. Therefore, revealing the functions and mechanism of PE biosynthesis in plant pathogens would provide potential targets for crop disease control. We performed analyses including phenotypic characterizations, lipidomics, enzyme activity, site-directed mutagenesis, and chemical inhibition assays to study the function of PS decarboxylase-encoding gene MoPSD2 in rice blast fungus Magnaporthe oryzae. The Mopsd2 mutant was defective in development, lipid metabolism, and plant infection. The PS level increased while PE decreased in Mopsd2, consistent with the enzyme activity. Furthermore, chemical doxorubicin inhibited the enzyme activity of MoPsd2 and showed antifungal activity against 10 phytopathogenic fungi including M. oryzae and reduced disease severity of two crop diseases in the field. Three predicted doxorubicin-interacting residues are important for MoPsd2 functions. Our study demonstrates that MoPsd2 is involved in de novo PE biosynthesis and contributes to the development and plant infection of M. oryzae and that doxorubicin shows broad-spectrum antifungal activity as a fungicide candidate. The study also implicates that bacterium Streptomyces peucetius, which biosynthesizes doxorubicin, could be potentially used as an eco-friendly biocontrol agent.

Engineering effector-triggered immunity in rice: Obstacles and perspectives

Improving rice immunity is one of the most effective approaches to reduce yield loss by biotic factors, with the aim of increasing rice production by 2050 amidst limited natural resources. Triggering a fast and strong immune response to pathogens, effector-triggered immunity (ETI) has intrigued scientists to intensively study and utilize the mechanisms for engineering highly resistant plants. The conservation of ETI components and mechanisms across species enables the use of ETI components to generate broad-spectrum resistance in plants. Numerous efforts have been made to introduce new resistance (R) genes, widen the effector recognition spectrum and generate on-demand R genes. Although engineering ETI across plant species is still associated with multiple challenges, previous attempts have provided an enhanced understanding of ETI mechanisms. Here, we provide a survey of recent reports in the engineering of rice R genes. In addition, we suggest a framework for future studies of R gene-effector interactions, including genome-scale investigations in both rice and pathogens, followed by structural studies of R proteins and effectors, and potential strategies to use important ETI components to improve rice immunity.

A chromosome-level genome assembly of an early matured aromatic Japonica rice variety Qigeng10 to accelerate rice breeding for high grain quality in Northeast China

Early-matured aromatic japonica rice from the Northeast is the most popular rice commodity in the Chinese market. The Qigeng10 (QG10) was one of the varieties with the largest planting area in this region in recent years. It was an early-matured japonica rice variety with a lot of superior traits such as semi-dwarf, lodging resistance, long grain, aromatic and good quality. Therefore, a high-quality assembly of Qigeng10 genome is critical and useful for japonica research and breeding. In this study, we produced a high-precision QG10 chromosome-level genome by using a combination of Nanopore and Hi-C platforms. Finally, we assembled the QG10 genome into 77 contigs with an N50 length of 11.80 Mb in 27 scaffolds with an N50 length of 30.55 Mb. The assembled genome size was 378.31Mb with 65 contigs and constituted approximately 99.59% of the 12 chromosomes. We identified a total of 1,080,819 SNPs and 682,392 InDels between QG10 and Nipponbare. We also annotated 57,599 genes by the Ab initio method, homology-based technique, and RNA-seq. Based on the assembled genome sequence, we detected the sequence variation in a total of 63 cloned genes involved in grain yield, grain size, disease tolerance, lodging resistance, fragrance, and many other important traits. Finally, we identified five elite alleles (qTGW2^Nipponbare , qTGW3^Nanyangzhan , GW5^IR24 , GW6^Suyunuo , and qGW8^Basmati385 ) controlling long grain size, four elite alleles (COLD1^Nipponbare , bZIP73^Nipponbare , CTB4a^{Kunmingxiaobaigu} , and CTB2^{Kunmingxiaobaigu} ) controlling cold tolerance, three non-functional alleles (DTH7^Kitaake , Ghd7^Hejiang19 , and Hd1^Longgeng31 ) for early heading, two resistant alleles (Pia^Akihikari and Pid4^Digu ) for rice blast, a resistant allele STV11^Kasalath for rice stripe virus, an NRT1.1B^IR24 allele for higher nitrate absorption activity, an elite allele SCM3^Chugoku117 for stronger culms, and the typical aromatic gene badh2-E2 for fragrance in QG10. These results not only help us to better elucidate the genetic mechanisms underlying excellent agronomic traits in QG10 but also have wide-ranging implications for genomics-assisted breeding in early-matured fragrant japonica rice.

Gap-Free Nuclear and Mitochondrial Genomes of Ustilaginoidea virens JS60-2, a Fungal Pathogen Causing Rice False Smut

Rice false smut (RFS), caused by Ustilaginoidea virens, has become a major disease in recent years, and mycotoxins produced by U. virens often threaten food safety. To study fungal pathogenesis and identify potential targets for developing new fungicides, gap-free nuclear and complete mitochondrial genomes of U. virens JS60-2 were sequenced and assembled. Using the second and third generation sequencing data, we assembled a 38.02-Mb genome that consists of seven contigs with the contig N₅₀ being 6.32-Mb. In total, 8,486 protein-coding genes were annotated in the genome, including 21 secondary metabolism gene clusters. We also assembled the complete mitochondrial genome, which is 102,498 bp, with 28% GC content. The JS60-2 genomes assembled in this study will facilitate research on U. virens and contribute to RFS control. [Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.