Guohong Cai

Bio: Guohong Cai is an academic researcher from Purdue University. The author has contributed to research in topics: Genome & Phytophthora infestans. The author has an hindex of 17, co-authored 38 publications receiving 2154 citations. Previous affiliations of Guohong Cai include United States Department of Agriculture & Agricultural Research Service.

Genome sequence and analysis of the Irish potato famine pathogen Phytophthora infestans.

Abstract: Phytophthora infestans is the most destructive pathogen of potato and a model organism for the oomycetes, a distinct lineage of fungus-like eukaryotes that are related to organisms such as brown algae and diatoms. As the agent of the Irish potato famine in the mid-nineteenth century, P. infestans has had a tremendous effect on human history, resulting in famine and population displacement(1). To this day, it affects world agriculture by causing the most destructive disease of potato, the fourth largest food crop and a critical alternative to the major cereal crops for feeding the world's population(1). Current annual worldwide potato crop losses due to late blight are conservatively estimated at $6.7 billion(2). Management of this devastating pathogen is challenged by its remarkable speed of adaptation to control strategies such as genetically resistant cultivars(3,4). Here we report the sequence of the P. infestans genome, which at similar to 240 megabases (Mb) is by far the largest and most complex genome sequenced so far in the chromalveolates. Its expansion results from a proliferation of repetitive DNA accounting for similar to 74% of the genome. Comparison with two other Phytophthora genomes showed rapid turnover and extensive expansion of specific families of secreted disease effector proteins, including many genes that are induced during infection or are predicted to have activities that alter host physiology. These fast-evolving effector genes are localized to highly dynamic and expanded regions of the P. infestans genome. This probably plays a crucial part in the rapid adaptability of the pathogen to host plants and underpins its evolutionary potential.

The family narnaviridae: simplest of RNA viruses.

Abstract: Members of the virus family Narnaviridae contain the simplest genomes of any RNA virus, ranging from 2.3 to 3.6 kb and encoding only a single polypeptide that has an RNA-dependent RNA polymerase domain. The family is subdivided into two genera based on subcellular location: members of the genus Narnavirus have been found in the yeast Saccharomyces cerevisiae and in the oomycete Phytophthora infestans and are confined to the cytosol, while members of the genus Mitovirus have been found only in filamentous fungi and are found in mitochondria. None identified thus far encodes a capsid protein; like several other RNA viruses of lower eukaryotes, their genomes are confined within lipid vesicles. As more family members are discovered, their importance as genetic elements is becoming evident. The unique association of the genus Mitovirus with mitochondria renders them potentially valuable tools to study biology of lower eukaryotes.

The evolution of species concepts and species recognition criteria in plant pathogenic fungi

Abstract: In this paper, we review historical and contemporary species concepts and species recognition criteria for plant pathogenic fungi. Previous incongruent and unstable classification based on subjective and changing criteria have led to some confusion, especially amongst plant pathologists. The goal of systematics is to provide an informative and robust framework that stands the test of time. The taxonomic histories of Cercospora, Colletotrichum, Fusarium, as well as the rust and smut fungi, are used as examples, to show how concepts and criteria used to delimit and recognize species have changed. Through these examples we compare the Genealogical Concordance Phylogenetic Species Recognition, an extension of the Phylogenetic Species Criterion, with other species recognition criteria and show that it provides a better discrimination for delimiting species. A rapidly increasing number of cryptic species are being discovered amongst plant pathogenic fungi using the Genealogical Concordance Phylogenetic Species Recognition, and it is important to determine their host range, the severity of diseases they cause and their biosecurity significance. With rapidly expanding global trade it has become imperative that we develop effective and reliable protocols to detect these previously unrecognized pathogens.

Origin of Race 3 of Fusarium oxysporum f. sp. lycopersici at a Single Site in California

Abstract: Cai, G., Gale, L. R., Schneider, R. W., Kistler, H. C., Davis, R. M., Elias, K. S., and Miyao, E. M. 2003. Origin of race 3 of Fusarium oxysporum f. sp. lycopersici at a single site in California. Phytopathology 93:1014-1022. Thirty-nine isolates of Fusarium oxysporum were collected from tomato plants displaying wilt symptoms in a field in California 2 years after F. oxysporum f. sp. lycopersici race 3 was first observed at that location. These and other isolates of F. oxysporum f. sp. lycopersici were characterized by pathogenicity, race, and vegetative compatibility group (VCG). Of the 39 California isolates, 22 were in VCG 0030, 11 in VCG 0031, and six in the newly described VCG 0035. Among the isolates in VCG 0030, 13 were race 3, and nine were race 2. Of the isolates in VCG 0031, seven were race 2, one was race 1, and three were nonpathogenic to tomato. All six isolates in VCG 0035 were race 2. Restriction fragment length polymorphisms (RFLPs) and sequencing of the intergenic spacer (IGS) region of rDNA identified five IGS RFLP haplotypes, which coincided with VCGs, among 60 isolates of F. oxysporum from tomato. Five race 3 isolates from California were of the same genomic DNA RFLP haplotype as a race 2 isolate from the same location, and all 13 race 3 isolates clustered together into a subgroup in the neighbor joining tree. Collective evidence suggests that race 3 in California originated from the local race 2 population.

Extensive horizontal gene transfers between plant pathogenic fungi.

Abstract: Horizontal gene transfer (HGT) plays an important role in the adaptation of lineages to changing environments. The extent of this process in eukaryotes, however, remains controversial. The most well-known and dramatic form of HGT represents intracellular gene transfer from endosymbionts to the host nuclear genome. Such episodes of transfer typically involve hundreds of genes and are thought to be possible only in the case of endosymbiosis. Using a conservative phylogenomic approach, we analyzed genomic data from the fungal pathogen Magnaporthiopsis incrustans in the order Magnaporthales and identified two instances of exclusive sharing of HGT-derived gene markers between Magnaporthales and another lineage of plant-pathogenic fungi in the genus Colletotrichum. Surprisingly, inspection of these data demonstrated that HGT is far more widespread than anticipated, with more than 90 genes (including 33 highly supported candidates) being putatively transferred between Magnaporthales and Colletotrichum. These gene transfers are often physically linked in the genome and show more than two-fold functional enrichment in carbohydrate activating enzymes associated with plant cell wall degradation. Our work provides a novel perspective on the scale of HGT between eukaryotes. These results challenge the notion that recognized HGT plays a minor role in the evolution of fungal lineages, and in the case we describe, is likely implicated in the evolution of plant pathogenesis. More generally, we suggest that the expanding database of closely related eukaryotic genomes and the application of novel analytic methods will further underline the significant impact of foreign gene acquisition across the tree of life. Major lifestyle transitions such as those accompanying the origin of extremophily or pathogenesis are expected to be ideal candidates for studying the mode and tempo of HGT.

SPAdes, a new genome assembly algorithm and its applications to single-cell sequencing ( 7th Annual SFAF Meeting, 2012)

Abstract: The lion's share of bacteria in various environments cannot be cloned in the laboratory and thus cannot be sequenced using existing technologies. A major goal of single-cell genomics is to complement gene-centric metagenomic data with whole-genome assemblies of uncultivated organisms. Assembly of single-cell data is challenging because of highly non-uniform read coverage as well as elevated levels of sequencing errors and chimeric reads. We describe SPAdes, a new assembler for both single-cell and standard (multicell) assembly, and demonstrate that it improves on the recently released E+V-SC assembler (specialized for single-cell data) and on popular assemblers Velvet and SoapDeNovo (for multicell data). SPAdes generates single-cell assemblies, providing information about genomes of uncultivatable bacteria that vastly exceeds what may be obtained via traditional metagenomics studies. SPAdes is available online ( http://bioinf.spbau.ru/spades ). It is distributed as open source software.

Plant immunity: towards an integrated view of plant―pathogen interactions

Abstract: Plants are engaged in a continuous co-evolutionary struggle for dominance with their pathogens. The outcomes of these interactions are of particular importance to human activities, as they can have dramatic effects on agricultural systems. The recent convergence of molecular studies of plant immunity and pathogen infection strategies is revealing an integrated picture of the plant-pathogen interaction from the perspective of both organisms. Plants have an amazing capacity to recognize pathogens through strategies involving both conserved and variable pathogen elicitors, and pathogens manipulate the defence response through secretion of virulence effector molecules. These insights suggest novel biotechnological approaches to crop protection.

Genome sequence and analysis of the tuber crop potato.

Abstract: Potato (Solanum tuberosum L.) is the world's most important non-grain food crop and is central to global food security. It is clonally propagated, highly heterozygous, autotetraploid, and suffers acute inbreeding depression. Here we use a homozygous doubled-monoploid potato clone to sequence and assemble 86% of the 844-megabase genome. We predict 39,031 protein-coding genes and present evidence for at least two genome duplication events indicative of a palaeopolyploid origin. As the first genome sequence of an asterid, the potato genome reveals 2,642 genes specific to this large angiosperm clade. We also sequenced a heterozygous diploid clone and show that gene presence/absence variants and other potentially deleterious mutations occur frequently and are a likely cause of inbreeding depression. Gene family expansion, tissue-specific expression and recruitment of genes to new pathways contributed to the evolution of tuber development. The potato genome sequence provides a platform for genetic improvement of this vital crop.

The paleozoic origin of enzymatic lignin decomposition reconstructed from 31 fungal genomes

Abstract: Wood is a major pool of organic carbon that is highly resistant to decay, owing largely to the presence of lignin. The only organisms capable of substantial lignin decay are white rot fungi in the Agaricomycetes, which also contains non-lignin-degrading brown rot and ectomycorrhizal species. Comparative analyses of 31 fungal genomes (12 generated for this study) suggest that lignin-degrading peroxidases expanded in the lineage leading to the ancestor of the Agaricomycetes, which is reconstructed as a white rot species, and then contracted in parallel lineages leading to brown rot and mycorrhizal species. Molecular clock analyses suggest that the origin of lignin degradation might have coincided with the sharp decrease in the rate of organic carbon burial around the end of the Carboniferous period.

Of PAMPs and Effectors: The Blurred PTI-ETI Dichotomy

Abstract: Typically, pathogen-associated molecular patterns (PAMPs) are considered to be conserved throughout classes of microbes and to contribute to general microbial fitness, whereas effectors are species, race, or strain specific and contribute to pathogen virulence. Both types of molecule can trigger plant immunity, designated PAMP-triggered and effector-triggered immunity (PTI and ETI, respectively). However, not all microbial defense activators conform to the common distinction between PAMPs and effectors. For example, some effectors display wide distribution, while some PAMPs are rather narrowly conserved or contribute to pathogen virulence. As effectors may elicit defense responses and PAMPs may be required for virulence, single components cannot exclusively be referred to by one of the two terms. Therefore, we put forward that the distinction between PAMPs and effectors, between PAMP receptors and resistance proteins, and, therefore, also between PTI and ETI, cannot strictly be maintained. Rather, as illustrated by examples provided here, there is a continuum between PTI and ETI. We argue that plant resistance is determined by immune receptors that recognize appropriate ligands to activate defense, the amplitude of which is likely determined by the level required for effective immunity.