PUBLISHED: 3 FEBRUARY 2016 | ARTICLE NUMBER: 16006 –16009 research highlights

PATHOGENOMICS it highlights the uncertain future of crop the epidermal structures. Five gain-of- Hybrid vs hybrid resistance to pathogens. GT function mutants with T-DNA inserted Nature Genet. http://doi.org/bbxc (2016) upstream of MpRSL1 all developed ectopic EPIDERMAL STRUCTURES rhizoids. Gene expression analysis confirmed Triticale is an artificial hybrid cereal that Sculpting with RSL1 that MpRSL1 was specifically expressed combines wheat grain quality and yield Curr. Biol. 26, 93–99 (2016) in epidermal cells that developed into the with the robustness of rye. From its first epidermal structures. commercial use half a century ago until 2001, The researchers showed that RSL1 genes triticale was resistant to powdery mildew, a also controlled the development of rhizoids devastating disease caused by the biotrophic and axillary hairs in mosses. Moreover, fungus Blumeria graminis. Beat Keller at transforming MpRSL1 into the Arabidopsis the University of Zürich, Switzerland, and mutant with defective RSL1 function restored colleagues now show that the pathogen has the root hairs, suggesting that the RSL1 genes adapted to the hybrid cereal by undergoing of Arabidopsis and liverwort are functionally

hybridization itself. OXFORD JOHN BAKER / UNIV. conserved. It would seem that RSL1 genes The genomic sequences of different once regulated epidermal structures in the B. graminis strains indicate whether they Epidermal structures, such as unicellular common ancestors of land plants, and retain infect wheat or rye. This also holds true rhizoids and multicellular propagules, that important function to this day. JL for the newly emerging triticale-infecting played important functions in facilitating isolates, which have large sequences from colonization of the land by plants. They GIBBERELLIN SIGNALLING rye-infecting fungi merged into a mostly promoted traits associated with land Nectar control wheat-specific genomic background, a adaptation, such as nutrient acquisition, Mol. Plant. http://doi.org/bbx4 (2015) hallmark of hybridization followed by desiccation tolerance and reproduction. backcrossing. So, by combining their However, the genetic basis bolstering Flower and fruit development is one of the genomes, the pathogens have produced a these epidermal structures remains largely best-studied processes in plant biology. As hybrid strain with a host range expanded unknown. Hélène Proust, of the University well as petals, pollen, seeds and fruit, flowers to include triticale. This event probably of Oxford, UK, and colleagues now find that also produce nectar, a sugary solution that took place in Europe sometime after the the ROOTHAIR DEFECTIVE SIX-LIKE attracts insects and other animals, either development of triticale, and has occurred class 1(RSL1) transcription factors as pollinators or for defence. Auxin and independently at least twice. positively regulate the development of these jasmonic acid have both been implicated The molecular mechanism behind this epidermal structures. in the control of nectar production. Now, host expansion is currently unknown, despite Wild-type liverwort, Marchantia Lisa Wiesen at the University of Minnesota, the authors checking the ‘usual suspects’ polymorpha, is abundant in epidermal USA, and colleagues have found a role for such as secreted effectors. Nevertheless, structures, but two mutants showed no gibberellin (GA) in managing nectar flow. the discovery that pathogen evolution cells expanding out of the epidermis. The A microarray investigation showed that by hybridization closely mirrors host researchers identified an MpRSL1 gene GIBBERELLIN 2-OXIDASE6 (GA2ox6), evolution, even in very short time frames, whose expression was disrupted in the an enzyme that breaks down gibberellins is of particular interest for agriculture, as mutants and whose overexpression restored and their immediate precursors, was overrepresented in nectar-producing GRASSLAND ECOLOGY nectaries. Furthermore, Arabidopsis mutants with non-functioning ga2ox6 genes Nitrogen retention New Phytol. http://doi.org/bbxf (2016) produced significantly less nectar than wild-type plants, whereas an inhibitor of GA Humans have approximately doubled the amount of biologically reactive nitrogen in synthesis, paclobutrazol, restored their nectar the atmosphere over the past two centuries. Terrestrial plant communities can retain production. Conversely, overexpressing significant quantities of nitrogen, preventing its spread to the surrounding environment. GA2ox6 increased nectar volumes, and Now, a series of glasshouse experiments suggests that the dominance, and not diversity, mutant plants with overactive GA synthesis of plant traits determines the ability of grasslands to capture added nitrogen. produced less nectar than wild-type. Franciska de Vries and Richard Bardgett of the University of Manchester, UK, examined These experiments show that GA serves the ability of 56 experimental grassland communities — comprised of various combinations to suppress nectar accumulation or release — of herbs and grasses, and differing in the diversity and dominance of various plant but it is less clear how this is achieved. GA functional traits — to retain nitrogen. They fed the experimental plots with isotopically may reduce the starch reserves from which labelled nitrate and ammonium, and monitored uptake and retention over a 48-hour period. nectar sugars are synthesized, or possibly Nitrogen retention increased with root biomass, the abundance of herbs and the dominance affect the transcription of genes directly of exploitative plant traits, namely a high specific leaf area and leaf nitrogen content, and involved in starch breakdown. However, a low leaf dry matter content. Whereas root biomass and herb abundance promoted plant the involvement of three of the major plant nitrogen uptake, exploitative plant traits promoted soil microbial uptake. hormones in the production of nectar Whether the nitrogen captured by exploitative plant communities is retained over demonstrates the importance of precise longer periods of time will depend on its rate of remineralization. However, the researchers control and release of this elixir. CS tentatively suggest that the ability of plants with exploitative growth strategies to capitalize on nitrogen additions in the short term may increase their abundance in the Written by Anna Armstrong, Jun Lyu, Chris Surridge longer term. AA and Guillaume Tena

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