Tracing the evolution of the arbuscular mycorrhizal symbiosis in the plant lineage

The Arbuscular Mycorrhizal (AM) symbiosis is formed by ~80% of land plants with a specific group of soil fungi, the AM fungi. Through this symbiosis, plants obtain nutrients that they otherwise would not be able to access. Based on data from fossils and extant plants, it has been predicted that the AM symbiosis evolved in early land plants. Research in the past two decades utilising angiosperm model plant species has identified several plant genes that regulate the AM symbiosis. These studies have also revealed that these symbiosis genes are highly conserved in the angiosperms but whether this conservation extends to the non-flowering plants has not been explored. In the present study, a comprehensive phylogenetic analysis of the symbiosis genes was conducted, using genomic and transcriptomic data from the non-flowering plant lineages, to gain insights into the evolution of these genes in plants. The results of this analysis indicate that these genes evolved in a stepwise fashion. While some genes appeared in the algal ancestors of the charophytes, others appeared in the early land plant ancestors of liverworts. To further study the AM symbiosis in the non-flowering plants, key methods and genomic resources were established for the liverwort Marchantia paleacea to enable its use as a model plant for the study of the evolution of the AM symbiosis. Using the resources established, phylogenomic comparisons were conducted between M. paleacea and a related liverwort species, M. polymorpha, that is predicted to have lost the ability to engage in the AM symbiosis. These analyses revealed that the homologs of angiosperm symbiosis genes are required for functional symbioses in the liverworts. The findings presented here provide insights into the processes that contributed to the evolution and maintenance of this ancestral symbiosis in the plant lineage

A combination of chitooligosaccharide and lipochitooligosaccharide recognition promotes arbuscular mycorrhizal associations in Medicago truncatula.

Plants associate with beneficial arbuscular mycorrhizal fungi facilitating nutrient acquisition. Arbuscular mycorrhizal fungi produce chitooligosaccharides (COs) and lipo-chitooligosaccharides (LCOs), that promote symbiosis signalling with resultant oscillations in nuclear-associated calcium. The activation of symbiosis signalling must be balanced with activation of immunity signalling, which in fungal interactions is promoted by COs resulting from the chitinaceous fungal cell wall. Here we demonstrate that COs ranging from CO4-CO8 can induce symbiosis signalling in Medicago truncatula. CO perception is a function of the receptor-like kinases MtCERK1 and LYR4, that activate both immunity and symbiosis signalling. A combination of LCOs and COs act synergistically to enhance symbiosis signalling and suppress immunity signalling and receptors involved in both CO and LCO perception are necessary for mycorrhizal establishment. We conclude that LCOs, when present in a mix with COs, drive a symbiotic outcome and this mix of signals is essential for arbuscular mycorrhizal establishment

Mutagenesis of Puccinia graminis f. sp. tritici and selection of gain-of-virulence mutants

Wheat stem rust caused by the fungus Puccinia graminis f. sp. tritici (Pgt), is regaining prominence due to the recent emergence of virulent isolates and epidemics in Africa, Europe and Central Asia. The development and deployment of wheat cultivars with multiple stem rust resistance (Sr) genes stacked together will provide durable resistance. However, certain disease resistance genes can suppress each other or fail in particular genetic backgrounds. Therefore, the function of each Sr gene must be confirmed after incorporation into an Sr-gene stack. This is difficult when using pathogen disease assays due to epistasis from recognition of multiple avirulence (Avr) effectors. Heterologous delivery of single Avr effectors can circumvent this limitation, but this strategy is currently limited by the paucity of cloned Pgt Avrs. To accelerate Avr gene cloning, we outline a procedure to develop a mutant population of Pgt spores and select for gain-of-virulence mutants. We used ethyl methanesulphonate (EMS) to mutagenize urediniospores and create a library of > 10,000 independent mutant isolates that were combined into 16 bulks of ~658 pustules each. We sequenced random mutants and determined the average mutation density to be 1 single nucleotide variant (SNV) per 258 kb. From this, we calculated that a minimum of three independently derived gain-of-virulence mutants is required to identify a given Avr gene. We inoculated the mutant library onto plants containing Sr43, Sr44, or Sr45 and obtained 9, 4, and 14 mutants with virulence toward Sr43, Sr44, or Sr45, respectively. However, only mutants identified on Sr43 and Sr45 maintained their virulence when reinolculated onto the lines from which they were identified. We further characterized 8 mutants with virulence toward Sr43. These also maintained their virulence profile on the stem rust international differential set containing 20 Sr genes, indicating that they were most likely not accidental contaminants. In conclusion, our method allows selecting for virulent mutants toward targeted resistance (R) genes. The development of a mutant library from as little as 320 mg spores creates a resource that enables screening against several R genes without the need for multiple rounds of spore multiplication and mutagenesis

Crossing boundaries:bras, lingerie and rape myths in postcolonial urban middle-class India

With the processes of modernization, urbanization and the entry of women in the formal labour market in Indian metropolitan spaces, this paper examines how the modern middle-class woman’s sartorial choices become enmeshed in popular rape myths (false beliefs) that serve to blame her for the wearing of western clothing. The paper articulates the ways in which middle-class women’s social realities are shaped by historical, colonial and nationalist ideologies of modernization, constructed and mediated through moral codes of dressing. By drawing upon original and contemporary empirical narratives from the urban spaces of Delhi and Mumbai, we emphasise how everyday sartorial choices, in relation to particularly the bra and lingerie, can reveal the nuanced ways in which Urban Indian Professional Women (UIPW) seek to understand, negotiate, and resist patriarchal power. Our findings shed light on conflicting and contradictory spatial experiences, where some women internalize and negotiate moral codes of dressing, out of fear, and others who transgress are subject to sanctions. Given the paucity of scholarly literature in this area, the paper makes an important theoretical and empirical contribution with its focus on postcoloniality and everyday discursive material spaces of gendered and sexualized dress practices. It argues for the consciousness raising of everyday urban geographies of dress that reveal complicated structures of power that are often deemed hidden

Standards for plant synthetic biology: A common syntax for exchange of DNA parts

© 2015 New Phytologist Trust. Inventors in the field of mechanical and electronic engineering can access multitudes of components and, thanks to standardization, parts from different manufacturers can be used in combination with each other. The introduction of BioBrick standards for the assembly of characterized DNA sequences was a landmark in microbial engineering, shaping the field of synthetic biology. Here, we describe a standard for Type IIS restriction endonuclease-mediated assembly, defining a common syntax of 12 fusion sites to enable the facile assembly of eukaryotic transcriptional units. This standard has been developed and agreed by representatives and leaders of the international plant science and synthetic biology communities, including inventors, developers and adopters of Type IIS cloning methods. Our vision is of an extensive catalogue of standardized, characterized DNA parts that will accelerate plant bioengineering

Standards for plant synthetic biology: a common syntax for exchange of DNA parts.

Inventors in the field of mechanical and electronic engineering can access multitudes of components and, thanks to standardization, parts from different manufacturers can be used in combination with each other. The introduction of BioBrick standards for the assembly of characterized DNA sequences was a landmark in microbial engineering, shaping the field of synthetic biology. Here, we describe a standard for Type IIS restriction endonuclease-mediated assembly, defining a common syntax of 12 fusion sites to enable the facile assembly of eukaryotic transcriptional units. This standard has been developed and agreed by representatives and leaders of the international plant science and synthetic biology communities, including inventors, developers and adopters of Type IIS cloning methods. Our vision is of an extensive catalogue of standardized, characterized DNA parts that will accelerate plant bioengineering.Biotechnological and Biological Sciences Research Council (BBSRC). Grant Numbers: BB/K005952/1, BB/L02182X/1 Synthetic Biology Research Centre ‘OpenPlant’ award. Grant Number: BB/L014130/1 Spanish MINECO. Grant Number: BIO2013‐42193‐R Engineering Nitrogen Symbiosis for Africa (ENSA) The Bill & Melinda Gates Foundation US Department of Energy, Office of Biological and Environmental. Grant Number: DE‐AC02‐05CH1123 COST Action. Grant Number: FA100

What have we learnt from studying the evolution of the arbuscular mycorrhizal symbiosis?

International audienceThe arbuscular mycorrhizal (AM) symbiosis is a nearly ubiquitous association formed by most land plants. Numerous insights into the molecular mechanisms governing this symbiosis have been obtained in recent years leading to the identification of a core set of plant genes essential for successful formation of the AM symbiosis by angiosperm hosts. Recent phylogenetic analyses indicate that while the origin of some of these symbiotic genes predated the first land plants, the rest appeared through processes including de novo evolution and gene duplication that occurred specifically in the land plants. Purifying selection on this core gene set has been maintained over millions of years of plant evolution to conserve the AM symbiosis. However, several independent losses of this association have been recorded in numerous embryophyte lineages. In these lineages, potential compensatory mechanisms have been identified that could have helped these plants overcome the adversities imposed by the loss of the AM symbiosis. This review will focus on the processes governing the conservation of the AM symbiosis in the land plant lineage

A combination of chitooligosaccharide and lipochitooligosaccharide recognition promotes arbuscular mycorrhizal associations in Medicago truncatula

Abstract: Plants associate with beneficial arbuscular mycorrhizal fungi facilitating nutrient acquisition. Arbuscular mycorrhizal fungi produce chitooligosaccharides (COs) and lipo-chitooligosaccharides (LCOs), that promote symbiosis signalling with resultant oscillations in nuclear-associated calcium. The activation of symbiosis signalling must be balanced with activation of immunity signalling, which in fungal interactions is promoted by COs resulting from the chitinaceous fungal cell wall. Here we demonstrate that COs ranging from CO4-CO8 can induce symbiosis signalling in Medicago truncatula. CO perception is a function of the receptor-like kinases MtCERK1 and LYR4, that activate both immunity and symbiosis signalling. A combination of LCOs and COs act synergistically to enhance symbiosis signalling and suppress immunity signalling and receptors involved in both CO and LCO perception are necessary for mycorrhizal establishment. We conclude that LCOs, when present in a mix with COs, drive a symbiotic outcome and this mix of signals is essential for arbuscular mycorrhizal establishment

Nuclear-localized cyclic nucleotide-gated channels mediate symbiotic calcium oscillations

Nuclear-associated Ca2+ oscillationsmediate plant responses to beneficial microbial partners—namely, nitrogen-fixing rhizobial bacteria that colonize roots of legumes and arbuscular mycorrhizal fungi that colonize roots of the majority of plant species. A potassium-permeable channel is known to be required for symbiotic Ca2+ oscillations, but the calcium channels themselves have been unknown until now.We show that three cyclic nucleotide–gated channels in Medicago truncatula are required for nuclear Ca2+ oscillations and subsequent symbiotic responses.These cyclic nucleotide–gated channels are located at the nuclear envelope and are permeable to Ca2+.We demonstrate that the cyclic nucleotide–gated channels form a complex with the postassium-permeable channel, which modulates nuclear Ca2+ release. These channels, like their counterparts in animal cells, might regulate multiple nuclear Ca2+ responses to developmental and environmental conditions