Multilocus Sequence Typing and Single Nucleotide Polymorphism Analysis in Tilletia indica Isolates Inciting Karnal Bunt of Wheat

Expression analysis of genes involved in teliospores germination of Tilletia indica inciting Karnal bunt of wheat

BACKGROUND

Karnal bunt of wheat is an important quarantine disease, incited by Tilletia indica. It limits India's trade in wheat export. The teliospores are major source of inoculum to initiate and spread the Karnal bunt disease. The study aimed to identify the germination-related genes in the teliospores of T. indica.

METHODS AND RESULTS

The candidate genes in the teliospores germination were identified through the differential gene expression analysis with suitable bioinformatics analysis. Keeping in soil-borne nature of fungi, the teliospores of T. indica (2015 and 2018) were subjected to the qPCR analysis. 20 candidate genes were identified having role in germination of teliospores of T. indica. Twenty genes, viz. Ti9297 (9.31, 7.87-fold), Ti8696 (5.13, 6.54-fold), Ti7699 (8.9, 7.7-fold), Ti7858 (10.33, 6.21-fold), Ti7954 (7.46, 5.54-fold), Ti7739 (5.46, 6.46-fold), Ti9665 (10.74, 7.64-fold), Ti9335 (6.75, 4.36-fold), Ti8396 (9.35, 7.72-fold), Ti8126 (8.87, 11.31-fold), Ti7326 (6.04, 7.7-fold), Ti10208 (13.83, 5.81-fold), Ti12356 (7.83, 8.02-fold), Ti14271 (9.98, 6.32-fold), Ti9234 (11.2, 8.72-fold), Ti 8876 (6.47, 3.55-fold), Ti 10,606 (4.97, 2.35-fold), Ti7758 (10.33, 8.78-fold), Ti4692 (6.89, 9.88-fold), and Ti3932 (5.77, 4.5-fold) were found highly expressed in the germinating teliospores of 2015 and 2018, respectively. Eight genes (Ti508, Ti4152, Ti5346, Ti2375, Ti3739, Ti1134, Ti4399, and Ti4422) were downregulated in the germinating teliospores but these eight genes were showed higher expression in the dormant teliospores.

CONCLUSIONS

Twenty candidate genes were upregulated in the germinating teliospores are supposed to be involved in the process of germination. Eight genes were downregulated which were related to the process of the dormancy of teliospores. The study will be helpful to devise the newer management strategies for Karnal bunt disease of wheat.

Draft genome sequencing of Tilletia caries inciting common bunt of wheat provides pathogenicity-related genes

Common bunt of wheat caused by Tilletia caries is an important disease worldwide. The T. caries TC1_MSG genome was sequenced using the Illumina HiSeq 2500 and Nanopore ONT platforms. The Nanopore library was prepared using the ligation sequencing kit SQK-LSK110 to generate approximately 24 GB for sequencing. The assembly size of 38.18 Mb was generated with a GC content of 56.10%. The whole genome shotgun project was deposited at DDBJ/ENA/GenBank under the accession number JALUTQ000000000. Forty-six contigs were obtained with N50 of 1,798,756 bp. In total, 10,698 genes were predicted in the assembled genome. Out of 10,698 genes, 10,255 genes were predicted significantly in the genome. The repeat sequences made up approximately 1.57% of the genome. Molecular function, cellular components, and biological processes for predicted genes were mapped into the genome. In addition, repeat elements in the genome were assessed. In all, 0.89% of retroelements were observed, followed by long terminal repeat elements (0.86%) in the genome. In simple sequence repeat (SSR) analysis, 8,582 SSRs were found in the genome assembly. The trinucleotide SSR type (3,703) was the most abundant. Few putative secretory signal peptides and pathogenicity-related genes were predicted. The genomic information of T. caries will be valuable in understanding the pathogenesis mechanism as well as developing new methods for the management of the common bunt disease of wheat.

Understanding the Rice Fungal Pathogen Tilletia horrida from Multiple Perspectives

Rice kernel smut (RKS), caused by the fungus Tilletia horrida, has become a major disease in rice-growing areas worldwide, especially since the widespread cultivation of high-yielding hybrid rice varieties. The disease causes a significant yield loss during the production of rice male sterile lines by producing masses of dark powdery teliospores. This review mainly summarizes the pathogenic differentiation, disease cycle, and infection process of the T. horrida, as well as the decoding of the T. horrida genome, functional genomics, and effector identification. We highlight the identification and characterization of virulence-related pathways and effectors of T. horrida, which could foster a better understanding of the rice-T. horrida interaction and help to elucidate its pathogenicity molecular mechanisms. The multiple effective disease control methods for RKS are also discussed, included chemical fungicides, the mining of resistant rice germplasms/genes, and the monitoring and early warning signs of this disease in field settings.

Transcriptome Analysis of Wheat-Tilletia indica Interaction Provides Defense and Pathogenesis-Related Genes

Karnal bunt (Tilletia indica Mitra) is an internationally quarantined disease of wheat. Until now, very little information has been available on the molecular basis of resistance and pathogenicity of T. indica. To investigate the molecular basis of host−pathogen interaction, the transcriptome of T. indica inoculated resistant (HD29) and susceptible (WH542) genotypes of wheat were analyzed. Approximately 58 million reads were generated using RNA sequencing by the Illumina NextSeq500 platform. These sequence reads were aligned to a reference genome of wheat to compare the expression level of genes in resistant and susceptible genotypes. The high-quality reads were deposited in the NCBI SRA database (SRP159223). More than 80,000 genes were expressed in both the resistant and susceptible wheat genotypes. Of these, 76,088 were commonly expressed genes, including 3184 significantly upregulated and 1778 downregulated genes. Four thousand one hundred thirteen and 5604 genes were exclusively expressed in susceptible and resistant genotypes, respectively. Based on the significance, 503 genes were upregulated and 387 genes were downregulated. Using gene ontology, the majority of coding sequences were associated with response to stimuli, stress, carbohydrate metabolism, developmental process, and catalytic activity. Highly differentially expressed genes (integral component of membrane, exonuclease activity, nucleic acid binding, DNA binding, metal ion binding) were validated in resistant and susceptible genotypes using qPCR analysis and similar expression levels were found in RNA-Seq. Apart from the wheat, the mapping of T. indica was 7.07% and 7.63% of resistant and susceptible hosts, respectively, upon infection, which revealed significant pathogenesis-related genes. This first study provided in-depth information and new insights into wheat−T. indica interaction for managing Karnal bunt disease of wheat.

Multi-Locus Sequence Analysis Reveals Diversity of the Rice Kernel Smut Populations in the United States

Rice (Oryza sativa) is the second leading cereal crop in the world and is one of the most important field crops in the US, valued at approximately $2.5 billion. Kernel smut (Tilletia horrida Tak.), once considered as a minor disease, is now an emerging economically important disease in the US. In this study, we used multi-locus sequence analysis to investigate the genetic diversity of 63 isolates of T. horrida collected from various rice-growing areas across in the US. Three different phylogeny analyses (maximum likelihood, neighbor-joining, and minimum evolution) were conducted based on the gene sequence sets, consisting of all four genes concatenated together, two rRNA regions concatenated together, and only ITS region sequences. The results of multi-gene analyses revealed the presence of four clades in the US populations, with 59% of the isolates clustering together. The populations collected from Mississippi and Louisiana were found to be the most diverse, whereas the populations from Arkansas and California were the least diverse. Similarly, ITS region-based analysis revealed that there were three clades in the T. horrida populations, with a majority (76%) of the isolates clustering together along with the 22 Tilletia spp. from eight different countries (Australia, China, India, Korea, Pakistan, Taiwan, The US, and Vietnam) that were grouped together. Two of the three clades in the ITS region-based phylogeny consisted of the isolates reported from multiple countries, suggesting potential multiple entries of T. horrida into the US. This is the first multi-locus analysis of T. horrida populations. The results will help develop effective management strategies, especially breeding for resistant cultivars, for the control of kernel smut in rice.

Genome-Wide Association Mapping of Virulence Genes in Wheat Karnal Bunt Fungus Tilletia indica Using Double Digest Restriction-Site Associated DNA-Genotyping by Sequencing Approach

Tilletia indica is a quarantine fungal pathogen that poses a serious biosecurity threat to wheat-exporting countries. Acquiring genetic data for the pathogenicity characters of T. indica is still a challenge for wheat breeders and geneticists. In the current study, double digest restriction-site associated-DNA genotyping by sequencing was carried out for 39 T. indica isolates collected from different locations in India. The generated libraries upon sequencing were with 3,346,759 raw reads on average, and 151 x 2 nucleotides read length. The obtained bases per read ranged from 87 Mb in Ti 25 to 1,708 Mb in Ti 39, with 505 Mb on average per read. Trait association mapping was performed using 41,473 SNPs, infection phenotyping data, population structure, and Kinship matrix, to find single nucleotide polymorphisms (SNPs) linked to virulence genes. Population structure analysis divided the T. indica population in India into three subpopulations with genetic mixing in each subpopulation. However, the division was not in accordance with the degree of virulence. Trait association mapping revealed the presence of 13 SNPs associated with virulence. Using sequences analysis tools, one gene (g4132) near a significant SNP was predicted to be an effector, and its relative expression was assessed and found upregulated upon infection.