Search

Genome-wide analysis of Corynespora cassiicola putative effectors involved in the CLF disease of rubber tree.. 12th EFPP-10th SFP conference: Deepen Knowledge in Plant Pathology for Innovative Agro-Ecology

Brachypodium hybridum (2n = 30) is a natural allopolyploid with highly divergent subgenomes derived from two extant diploid species, B. distachyon (2n = 10) and B. stacei (2n = 20) that differ in chromosome evolution and number. We created synthetic B. hybridum allotetraploids by hybridizing various lines of B. distachyon and B. stacei. The initial amphihaploid F1 interspecific hybrids were obtained at low frequencies when B. distachyon was used as the maternal parent (0.15% or 0.245% depending on the line used) and were sterile. No hybrids were obtained from reciprocal crosses or when autotetraploids of the parental species were crossed. Colchicine treatment was used to double the genome of the F1 amphihaploid lines leading to allotetraploids. The genome-doubled F1 plants produced a few S1 (first selfed generation) seeds after self-pollination. S1 plants from one parental combination (Bd3-1×Bsta5) were fertile and gave rise to further generations whereas those of another parental combination (Bd21×ABR114) were sterile, illustrating the importance of the parental lineages crossed. The synthetic allotetraploids were stable and resembled the natural B. hybridum at the phenotypic, cytogenetic and genomic levels. The successful creation of synthetic B. hybridum offers the possibility to study changes in genome structure and regulation at the earliest stages of allopolyploid formation in comparison with the parental species and natural B. hybridum. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Due to their economic relevance, the study of plant pathogen interactions is of importance. However, elucidating these interactions and their underlying molecular mechanisms remains challenging since both host and pathogen need to be fully genetically accessible organisms. Here we present milestones in the establishment of a new biotrophic model pathosystem: Ustilago bromivora and Brachypodium sp. We provide a complete toolset, including an annotated fungal genome and methods for genetic manipulation of the fungus and its host plant. This toolset will enable researchers to easily study biotrophic interactions at the molecular level on both the pathogen and the host side. Moreover, our research on the fungal life cycle revealed a mating type bias phenomenon. U. bromivora harbors a haplo-lethal allele that is linked to one mating type region. As a result, the identified mating type bias strongly promotes inbreeding, which we consider to be a potential speciation driver. DOI: http://dx.doi.org/10.7554/eLife.20522.001, eLife digest Fungi cause many diseases in plants, and reduce the yield of important crops like wheat, corn and rice – all of which belong to the family of grasses. Much research into how disease-causing fungi infect plants will look at a given fungus that infects a specific plant in order to understand plant diseases in general. Over the years, scientists have generated suites of research tools to study these pairs of fungi and plants. However, many of these organism pairs (often called “model pathosystems”) have drawbacks when it comes to research in the laboratory, either on the side of the fungus or the side of plant. Brachypodium is a small grass that grows quickly and, unlike crop plants, it grows well in the laboratory. These characteristics make Brachypodium a promising model organism for studying many aspects of plant biology. Recently, a fungus called Ustilago bromivora – which is related to a fungus that infects corn – was reported to infect Brachypodium. This raised the question: could this fungus and this small grass become a new model pathosystem? Rabe, Bosch et al. set out to answer this question and now provide a toolkit that will help to establish U. bromivora and Brachypodium as a new model pathosystem. In all of U. bromivora’s close relatives, two compatible strains must meet and mate before the fungus can infect the plant; first Rabe, Bosch et al. confirmed that this is also the case for U. bromivora. Studying the life cycle of the U. bromivora fungus also unexpectedly revealed that while both mating partners are needed to infect the plant, only one of the strains survives outside of the plant after the infection. This phenomenon, referred to as a “mating type bias”, has been described for a few other related fungi. Next, Rabe, Bosch et al. conducted a genetic screen and identified two compatible strains that can grow without the plant as yeast-like cells. This means that these cells can be manipulated genetically, and indeed protocols to grow and genetically engineer the fungus and plant to address different research questions are included in the toolkit as well. Other new tools include the complete genetic sequence of the fungus with all its genes annotated, and a dataset of which genes are active in U. bromivora growing yeast-like in liquid culture versus those active when the fungus grows as a pathogen inside the plant. Together these new tools and datasets will provide a foundation to study different aspects of the interactions between grasses and disease-causing fungi. This in turn may lead to new methods to reduce fungal growth and reduce yield losses caused by fungal diseases in crop plants. Finally, the discovery that U. bromivora shows a mating type bias could provide a starting point for future studies into sexual reproduction in fungi and how new species arise. DOI: http://dx.doi.org/10.7554/eLife.20522.002