Cancer recurrence and lethality are enabled by enhanced survival and reversible cell cycle arrest of polyaneuploid cells

We present a unifying theory to explain cancer recurrence, therapeutic resistance, and lethality. The basis of this theory is the formation of simultaneously polyploid and aneuploid cancer cells, polyaneuploid cancer cells (PACCs), that avoid the toxic effects of systemic therapy by entering a state of cell cycle arrest. The theory is independent of which of the classically associated oncogenic mutations have already occurred. PACCs have been generally disregarded as senescent or dying cells. Our theory states that therapeutic resistance is driven by PACC formation that is enabled by accessing a polyploid program that allows an aneuploid cancer cell to double its genomic content, followed by entry into a nondividing cell state to protect DNA integrity and ensure cell survival. Upon removal of stress, e.g., chemotherapy, PACCs undergo depolyploidization and generate resistant progeny that make up the bulk of cancer cells within a tumor.

Evolution of Fluconazole-ResistantCandida albicansStrains by Drug-Induced Mating Competence and Parasexual Recombination

ABSTRACTThe clonal population structure ofCandida albicanssuggests that (para)sexual recombination does not play an important role in the lifestyle of this opportunistic fungal pathogen, an assumption that is strengthened by the fact that mostC. albicansstrains are heterozygous at the mating type locus (MTL) and therefore mating-incompetent. On the other hand, mating might occur within clonal populations and allow the combination of advantageous traits that were acquired by individual cells to adapt to adverse conditions. We have investigated if parasexual recombination may be involved in the evolution of highly drug-resistant strains exhibiting multiple resistance mechanisms against fluconazole, an antifungal drug that is commonly used to treat infections byC. albicans. Growth of strains that were heterozygous forMTLand different fluconazole resistance mutations in the presence of the drug resulted in the emergence of derivatives that had become homozygous for the mutated allele and the mating type locus and exhibited increased drug resistance. WhenMTLa/aandMTLα/α cells of these strains were mixed in all possible combinations, we could isolate mating products containing the genetic material from both parents. The initial mating products did not exhibit higher drug resistance than their parental strains, but further propagation under selective pressure resulted in the loss of the wild-type alleles and increased fluconazole resistance. Therefore, fluconazole treatment not only selects for resistance mutations but also promotes genomic alterations that confer mating competence, which allows cells in an originally clonal population to exchange individually acquired resistance mechanisms and generate highly drug-resistant progeny.IMPORTANCESexual reproduction is an important mechanism in the evolution of species, since it allows the combination of advantageous traits of individual members in a population. The pathogenic yeastCandida albicansis a diploid organism that normally propagates in a clonal fashion, because heterozygosity at the mating type locus (MTL) inhibits mating between cells. Here we show thatC. albicanscells that have acquired drug resistance mutations during treatment with the commonly used antifungal agent fluconazole rapidly develop further increased resistance by genome rearrangements that result in simultaneous loss of heterozygosity for the mutated allele and the mating type locus. This enables the drug-resistant cells of a population to switch to the mating-competent opaque morphology and mate with each other to combine different individually acquired resistance mechanisms. The tetraploid mating products reassort their merged genomes and, under selective pressure by the drug, generate highly resistant progeny that have retained the advantageous mutated alleles. Parasexual propagation, promoted by stress-induced genome rearrangements that result in the acquisition of mating competence in cells with adaptive mutations, may therefore be an important mechanism in the evolution ofC. albicanspopulations.

HERITABILITAS, SUMBER GEN, DAN DURABILITAS KETAHANAN VARIETAS PADI TERHADAP PENYAKIT HAWAR DAUN BAKTERI/ Heritability, Gene Resource, and Durability of Rice Varieties Resistance To Bacterial Leaf Blight Disease

<p>Bacterial leaf blight (BLB) disease is one of the obstacles in increasing of rice production. The use of resistant varieties is an effective and easy to implement for farmers. This paper discusses the heritability and source of resistance genes of rice varieties against the BLB disease and strategies to maintain the durability of resistant varieties as one of the control efforts through plant breeding to supports the increasing of rice production. Assembling and development of resistant varieties play an important role in controlling BLB disease because it has a genetic resistance<br />mechanism that can be inherited to progeny level. Varieties with vertical resistance are easily broken by pathogens, so it is necessary to assembling of varieties with horizontal resistance. To obtain the resistant progeny to BLB disease in the assembly of varieties, the position of the resistant varieties should be played as a female parent that has a high specific joining power. The nature of resistance to BLB is from a population whose parent genes are derived from multiple cross results has higher heritability. The populations derived from a double-cross have multigenic resistance and have the potential to produce recombinant individuals resistant for prolonged periods (durable). The availability of durable resistant varieties become a key requirement in sustainable BLB disease control. This matter can be done by improving the resistance of varieties through the assembling of varieties with various sources of resistance such as wild rice, local rice, and introduced rice.</p><p>Keywords: Rice, varieties, resistance, bacterial leaf blight, durability, heritability</p><p> </p><p><strong>ABSTRAK</strong></p><p>Penyakit hawar daun bakteri (HDB) merupakan salah satu kendala dalam peningkatan produksi padi. Penggunaan varietas tahan merupakan cara pengendalian yang efektif dan mudah diterapkan petani. Tulisan ini membahas heritabilitas dan sumber gen ketahanan varietas padi terhadap penyakit HDB dan strategi mempertahankan durabilitas varietas tahan sebagai salah satu upaya pengendalian melalui pemuliaan tanaman mendukung upaya peningkatan produksi padi. Perakitan dan pengembangan varietas tahan berperan penting mengendalikan penyakit HDB, karena memiliki mekanisme ketahanan genetik yang dapat diwariskan kepada keturunannya. Varietas dengan ketahanan vertikal mudah dipatahkan oleh patogen, sehingga perlu upaya perakitan varietas dengan ketahanan horizontal. Untuk memperoleh keturunan tanaman padi yang tahan terhadap penyakit HDB dalam perakitan varietas, posisi tetua tahan sebaiknya diperankan sebagai tetua betina yang memiliki daya gabung khusus yang tinggi. Sifat ketahanan HDB dari populasi tetua yang mengandung gen dari hasil silang ganda memilliki heritabilitas lebih tinggi. Populasi turunan dari silang ganda memiliki ketahanan multigenik dan berpeluang menghasilkan individu rekombinan tahan untuk periode yang lama (durable). Ketersediaan varietas tahan yang durable menjadi syarat utama dalam pengendalian penyakit HDB secara berkelanjutan. Hal ini dapat dilakukan dengan perbaikan ketahanan varietas melalui perakitan varietas dengan berbagai sumber ketahanan, di antaranya padi liar, padi lokal, dan padi introduksi.</p><p>Kata kunci: Padi, varietas, ketahanan, hawar daun bakteri, durabilitas, heritabilitas</p>

Early selection of potato clones with the H1 resistance gene – the relation of nematode resistance to quality characteristics

Breeding a new potato cultivar is a long-term process ending with a few elite individuals from initially large populations. Screening for resistance in the seedling and first clonal generations is a cost-effective and efficient way to reduce the time needed to create a new variety. Unlike the phenotypic assessment of resistance to nematodes, marker-assisted selection (MAS) can be applied at early stages of selection. The frequent question among breeders is about the impact of early selection for resistance on the agronomic value of finally selected resistant progeny. The study presents a relationship between the presence of markers TG689 and 57R and some agricultural traits in field grown seedlings and three successive vegetative generations. Both markers are linked to H1 gene, which confers resistance to the golden cyst nematode Globodera rostochiensis. Clones with these markers had higher total tuber and starch yield than those without the markers. A negative relationship between marker presence and quality was not observed.

Pollen-Mediated Dispersal of Glyphosate-Resistance in Palmer Amaranth under Field Conditions

In addition to being a strong competitor with cotton and other row crops, Palmer amaranth has developed resistance to numerous important agricultural herbicides, including glyphosate. The objective of this study was to determine if the glyphosate-resistance trait can be transferred via pollen movement from a glyphosate-resistant Palmer amaranth source to a glyphosate-susceptible sink. In 2006 and 2007 glyphosate-resistant Palmer amaranth plants were transplanted in the center of a 30-ha cotton field. Susceptible Palmer amaranth plants were transplanted into plots located at distances up to 300 m from the edge of the resistant pollen source in each of the four cardinal and ordinal directions. Except for the study plots, the interior of the field and surrounding acreage were kept free of Palmer amaranth by chemical and physical means. Seed was harvested from 249 and 292 mature females in October 2006 and 2007, respectively. Offspring, 14,037 in 2006 and 13,685 in 2007, from glyphosate-susceptible mother plants were treated with glyphosate when the plants were 5 to 7 cm tall. The proportion of glyphosate-resistant progeny decreased with increased distance from the pollen source; approximately 50 to 60% of the offspring at the 1- and 5-m distances were resistant to glyphosate, whereas 20 to 40% of the offspring were resistant at the furthest distances. The development of resistance was not affected by direction; winds were variable with respect to both speed and direction during the peak pollination hours throughout the growing season. Results from this study indicate that the glyphosate-resistance trait can be transferred via pollen movement in Palmer amaranth.

Screening of rootstock hybrids with Vitis cinerea Arnold for phylloxera resistance

The resistance to phylloxera is one of the most important properties of grapevine rootstock. The breeding and selection of rootstock varieties represents a biological method of fight against phylloxera. In this study altogether 59 rootstock hybrids originating from nine different populations were evaluated. Pedigrees of all populations involved Vitis cinerea Arnold introduced through the hybrid Bruci/(Vitis berlandieri Planch. × Vitis rupestris Scheele) × Vitis cinerea Arnold/ and the variety Börner. Pot experiments were performed in a glasshouse while those with excised root pieces in root bioassay took place in a laboratory. This combination showed to be a very good selection tool for rootstock breeding. In seven rootstock hybrids, it was found that the resistance to phylloxera gallicoles and radicicoles was very high. The highest number of resistant hybrids was found in Binova × Börner. The variety Börner showed to be the best gene source of phylloxera resistance and even in case of a simple crossing produced sufficient number of resistant progeny.

Phenotypic and Genotypic Analysis ofIn Vitro-Selected Artemisinin-Resistant Progeny of Plasmodium falciparum

ABSTRACTEmergence of artemisinin resistance in Cambodia highlights the importance of characterizing resistance to this class of drugs. Previously, intermediate levels of resistance inPlasmodium falciparumwere generatedin vitrofor artelinic acid (AL) and artemisinin (QHS). Here we expanded on earlier selection efforts to produce levels of clinically relevant concentrations, and the resulting lines were characterized genotypically and phenotypically. Recrudescence assays determined the ability of resistant and parent lines to recover following exposure to clinically relevant levels of drugs. Interestingly, the parent clone (D6) tolerated up to 1,500 ng/ml QHS, but the resistant parasite, D6.QHS340×3, recovered following exposure to 2,400 ng/ml QHS. Resistant D6, W2, and TM91c235 parasites all exhibited elevated 50% inhibitory concentrations (IC50s) to multiple artemisinin drugs, with >3-fold resistance to QHS and AL; however, the degree of resistance obtained with standard methods was remarkably less than expected for parasite lines that recovered from 2,400-ng/ml drug pressure. A novel assay format with radiolabeled hypoxanthine demonstrated a greater degree of resistancein vitrothan the standard SYBR green method. Analysis of merozoite number in resistant parasites found D6 and TM91c235 resistant progeny had significantly fewer merozoites than parent strains, whereas W2 resistant progeny had significantly more. Amplification ofpfmdr1increased proportionately to the increased drug levels tolerated by W2 and TM91c235, but not in resistant D6. In summary, we define the artemisinin resistance phenotype as a decrease in susceptibility to artemisinins along with the ability to recover from drug-induced dormancy following supraclinical concentrations of the drug.

A Single Dominant Locus, Ren4, Confers Rapid Non-Race-Specific Resistance to Grapevine Powdery Mildew

In the present study we screened the progeny of Vitis vinifera × V. romanetii populations segregating for resistance to powdery mildew and determined the presence of a single, dominant locus, Ren4, conferring rapid and extreme resistance to the grapevine powdery mildew fungus Erysiphe necator. In each of nine Ren4 pseudo-backcross 2 (pBC2) and pBC3 populations (1,030 progeny), resistance fit a 1:1 segregation ratio and overall segregated as 543 resistant progeny to 487 susceptible. In full-sib progeny, microscopic observations revealed the reduction of penetration success rate (as indicated by the emergence of secondary hyphae) from 86% in susceptible progeny to below 10% in resistant progeny. Similarly, extreme differences were seen macroscopically. Ratings for Ren4 pBC2 population 03-3004 screened using natural infection in a California vineyard and greenhouse and using artificial inoculation of an aggressive New York isolate were fully consistent among all three pathogen sources and environments. From 2006 to 2010, Ren4 pBC2 and pBC3 vines were continuously screened in California and New York (in the center of diversity for E. necator), and no sporulating colonies were observed. For population 03-3004, severity ratings on leaves, shoots, berries, and rachises were highly correlated (R2 = 0.875 to 0.996) in the vineyard. Together, these data document a powdery mildew resistance mechanism not previously described in the Vitaceae or elsewhere, in which a dominantly inherited resistance prevents hyphal emergence and is non-race-specific and tissue-independent. In addition to its role in breeding for durable resistance, Ren4 may provide mechanistic insights into the early events that enable powdery mildew infection.

Loss of Heterozygosity ofFCY2Leading to the Development of Flucytosine Resistance in Candida tropicalis

ABSTRACTAs fluconazole resistance becomes an emerging issue for treating infections caused byCandida tropicalis, searching for alternative becomes a prominent task. In the present study, 97 clinical isolates ofC. tropicaliswere tested for the susceptibilities to flucytosine (5FC) with the Etest method. Although only one isolate was resistant to 5FC, 30 susceptible isolates could produce resistant progeny after exposure to the drug. Interestingly, 22 of these 30 clinical isolates had a heterozygous G/T at the 145th position onFCY2, encoding purine-cytosine permease, whereas their progeny recovered from within the inhibitory ellipses had homozygous T/T, resulting in null alleles for both copies of the gene and produced only truncated proteins, effecting the 5FC resistance. Furthermore, we found that two major fluconazole-resistant clinical clones, diploid sequence type 98 (DST98) and DST140, had a homozygous G/G at the 145th position, and neither was able to produce 5FC-resistant progeny within the inhibitory ellipses. Hence, strains ofC. tropicaliscontaining heterozygous alleles may develop 5FC resistance readily, whereas those with homozygous G/G wild-type alleles can be treated with 5FC. Subsequently, a combination of 5FC and another antifungal drug is applicable for treating infections ofC. tropicalis.

Horizontal Transfer of Tetracycline Resistance among Chlamydia spp. In Vitro

ABSTRACT There are no examples of stable tetracycline resistance in clinical strains of Chlamydia trachomatis. However, the swine pathogen Chlamydia suis is commonly tetracycline resistant, both in America and in Europe. In tested U.S. strains, this resistance is mediated by a genomic island carrying a tet(C) allele. In the present study, the ability of C. suis to mobilize tet(C) into other chlamydial species was examined. Differently antibiotic resistant strains of C. suis, C. trachomatis, and Chlamydia muridarum were used in coculture experiments to select for multiply antibiotic resistant progeny. Coinfection of mammalian cells with a naturally occurring tetracycline-resistant strain of C. suis and a C. muridarum or C. trachomatis strain containing selected mutations encoding rifampin (rifampicin) or ofloxacin resistance readily produced doubly resistant recombinant clones that demonstrated the acquisition of tetracycline resistance. The resistance phenotype in the progeny from a C. trachomatis L2/oflR-C. suis R19/tetR cross resulted from integration of a 40-kb fragment into a single ribosomal operon of a recipient, leading to a merodiploid structure containing three rRNA operons. In contrast, a cross between C. suis R19/tetR and C. muridarum MoPn/oflR led to a classical double-crossover event transferring 99 kb of DNA from C. suis R19/tetR into C. muridarum MoPn/oflR. Tetracycline resistance was also transferred to recent clinical strains of C. trachomatis. Successful crosses were not obtained when a rifampin-resistant Chlamydophila caviae strain was used as a recipient for crosses with C. suis or C. trachomatis. These findings provide a platform for further exploration of the biology of horizontal gene transfer in Chlamydia while bringing to light potential public health concerns generated by the possibility of acquisition of tetracycline resistance by human chlamydial pathogens.