Experimental evolution induces loss of female-fertility in vitro in the fungal pathogen of rice, Magnaporthe oryzae

Sexual reproduction is widespread in eukaryotic organisms. Inmany fungal species previously known to reproduce asexually, some populations have been shown to encounter episodes of sexual reproduction. It has been suggested that mostfungi that are pathogenic on plants may reproduce sexually near their center of origin but have lost this ability during their dispersion. If a population reproduces exclusively clonally forseveral generations, individuals may accumulate deleterious mutations in loci controlling sexual reproduction. This may result in a complete loss of sexual reproduction ability. We tested this hypothesis on /Magnaporthe oryzae/, which is responsible for the most important fungal disease on cultivated rice worldwide: blast. In this species, only asexual spores are observed in the field. However, some strains coming from the putative center of origin of the fungus (in South East Asia, near the Himalayan Foothills) are able to produce viable sexual spores /in vitro/, and indirect evidence that sexual reproduction do occur /in natura/ in this region have been recently provided (see the abstract by E. Fournier).//In this heterothallic fungus,//sexual reproduction can occur only between two different strains of opposite mating type. Moreover, at least one of them, independently from the mating type, must be female-fertile, that is to be able to produce the sexual organs (perithecia) where meiosis takes place. We performed /in vitro /experimental evolution of four female-fertile strains for 10-20 "clonal generations". These strains came from a recombinant population of the center of origin. Each of the four strains became female-sterile in about 100 days in at least one of the two replicates we performed. This loss of female-fertility was accompanied by a reduction of asexual sporulation /in vitro /and /in planta/.//As epigenetical effects could explain the frequent loss of female-fertility observed, we tested if stress could restore it. Four different stresses were tested: extremely low temperature (-80°C), mycelium fragmentation by sonication, monosporic isolation, growth on plant. None of these stresses achieved to restore female-fertility, so the loss of female-fertility might be explained by genetical rather than epigenetical mechanisms. Crosses were performed between mutant strains that had lost female-fertility and wild type strains. In the offspring, the female-fertility phenotype segregated in 1:3 proportions. Backcrosses between F1 female-sterile strains and wild type strains gave the same result, supporting the hypothesis of a genetic control. Here we showed for the first time that female-fertility could be rapidly lost in theabsence of sexual reproduction in /M. oryzae/ strains from rice. We showed that it might be due to mutation accumulation, probably at several loci. From these results we hypothesize that sexual reproduction ability may have been lost rapidly during the dispersion of the disease from Asia to the rest of the world. More generally, this study provides a case study to test hypotheses on the enigma of sex. (Texte intégral

Spektrum Ketahanan Galur Haploid Ganda Turunan IR64 Dan Oryza Rufipogon Yang Mengandung QTL Ketahanan Terhadap Penyakit Blas (Pir)

Resistance Spectrum of Double Haploid Lines Derivedfrom IR64 and Wild Rice Species, Oryza rufipogonContained the Blast Resistance QTL (Pir). Dwinita W.Utami, A. Dinar Ambarwati, Aniversari Apriana, AtmitriSisharmini, Ida Hanarida, Didier Tharreau, and Santosa.This study was initiated to determine the spectrum resistanceof the candidate durable blast resistance variety containedthe QTL (quantitative trait locus), Pir1 and 2. This QTLwas mapped on chromosome 2 detected using the advancedbackcross population (BC5) from the wild rice speciesOryza rufipogon to IR64. Pir (1 and 2) also establishedon double haploid (DH) population derived from the selectedlines of BC2F3 population, progenies from the sameparents. The DH lines were developed to speed up the fixationprocess of the recessive alleles in the selected lines.Near isogenic lines with different blast resistance genes andcombination were used in this study comparing to the DHpopulation on their resistance spectrum using the knownavr gene isolates both on green house and field screening.The determination of the resistance spectrum will useful onthe prediction of durability of blast resistance gene in DHpopulation. The results of spectrum resistance test in greenhouse and field showed that Pir1and Pir2 segregated on 1 : 1proportion related with specific respond to blast avr genePH14 and CM28 resistance. Pir1 was identic to Pi33 or Pi25and Pir2 to Pitq5 on spectrum resistance

Generic names in Magnaporthales

This is the final version of the article. Available from the publisher via the DOI in this record.The order Magnaporthales comprises about 200 species and includes the economically and scientifically important rice blast fungus and the take-all pathogen of cereals, as well as saprotrophs and endophytes. Recent advances in phylogenetic analyses of these fungi resulted in taxonomic revisions. In this paper we list the 28 currently accepted genera in Magnaporthales with their type species and available gene and genome resources. The polyphyletic Magnaporthe 1972 is proposed for suppression, and Pyricularia 1880 and Nakataea 1939 are recommended for protection as the generic names for the rice blast fungus and the rice stem rot fungus, respectively. The rationale for the recommended names is also provided. These recommendations are made by the Pyricularia/Magnaporthe Working Group established under the auspices of the International Commission on the Taxonomy of Fungi (ICTF).This work was partially supported by the National Science Foundation of the United States (grant number DEB 1145174 and DEB 1452971) to Ning Zhang

Identification of Magnaporthe grisea avirulence genes to seven rice cultivars

Pour caractériser le pouvoir pathogène de Magnaporthe grisea sur des cultivars spécifiques du riz, un croisement a été réalisé entre deux isolats pathogènes du riz. Les gènes ainsi obtenus ont été analysés afin de mettre en évidence leur virulenc

Present knowledge of rice resistance genetics and strategies for Magnaporthe grisea pathogenicity and avirulence gene analysis

L'identification de gènes de résistance aux attaques du champignon M. grisea chez le riz permet de concevoir des stratégies de sélection de cultivars résistants. Cette étude fait état des progrès récents en matière d'analyse génétique du pouvoir pathogène, de la spécificité de l'hôte et de l'avirulence. Il convient de cloner et séquencer plusieurs gènes d'avirulence pour en étudier la fonction; il serait par ailleurs souhaitable d'obtenir des isolats pathogènes plus fertiles, tenant compte des résultats de l'analyse des populations pathogènes, pour une meilleure connaissance des phénomènes à l'échelon moléculair

Avirulence genes identified

Le présent programme de recherche a permis d'identifier une souche femelle de Magnaporthe grisea, appelée Guy 11, parmis les 950 souches isolées provenant de 33 pays. Les croisements effectués entre Guy 11 et les souches pathogènes du riz ont permis de déterminer les gènes de l'avirulenc

Identification and characterization of apf1- in a non-pathogenic mutant of the rice blast fungus Magnaporthe grisea which is unable to differentiate appressoria

In a cross between two isolates of the rice blast fungus #Magnaporthe grisea#, a spontaneous mutant was identified which was non-pathogenic on rice and did not differentiate appressoria on hydrophobic surfaces. The mutant was also non-pathogenic on rice when inoculated on wounded leaves, suggesting that its ability to grow in plant tissue was also impaired. Mutant spores were three-celled, with apical cells longer than those of parental isolates. Using one full sib-cross and one back-cross, we showed that all of the mutant phenotypes (non-pathogenicity on rice, appressorium deficiency and elongated spores) co-segregated as a single gene which was named APF1. Comparison of apf1- mutants with previously characterized appressorium-deficient mutants of #M. grisea# provided evidence that APF1 is a new gene involved in appressorium differentiation which has pleiotropic effects on plant colonisation and spore morphology. Significantly, apflmutants could not form appressoria in the presence of cyclic AMP, indicating that APF1 acts downstream, or independently, of the cAMP signalling pathway required for appressorium differentiation and function in #M. grisea# (Résumé d'auteur