Tag Archives: Plant-Microbe Interactions

Meetings in Massachusetts, October 2012

Two upcoming meetings in the state of Massachusetts may be of interest to you, one of which I have already told you about.

UMass Plant Biology Graduate Program

The Plant Biology Graduate Program at the University of Massachusetts Amherst will be holding their 10th Annual Symposium in Plant Biology on Saturday October 6th, 2012.  This year’s focus is pertinent to readers of Cyme & Cystidium — it’s titled “War or Peace? Interactions Between Plants and Microbes“.  The symposium is free but you have to register to attend.

massmyco

MassMyco, the first regional meeting of mycologists from the state of Massachusetts, will be held on October 27th, 2012.  Registration is now open.

Seasonal Trends In Bryophyte-Associated Fungal Communities

I recently returned from the Mycological Society of America annual meeting – this year held at Yale University in New Haven.  There were lots of great talks about fungal genomics, systematics, and ecology – and it’s always good to see old mycological friends and make new ones.

Håvard Kauserud of The University of Oslo, who spoke about recent research from his laboratory, gave one of my favorite talks of the meeting.  His talk took place during a very rewarding afternoon session on fungal ecology.  Already highly prolific, there’s been an increase in the flood of papers to come out of the Kauserud lab over the last year.  Just this month, there’s a nice commentary on the phenomenon of metagenomic tag switching during amplicon sequencing published in the journal Fungal Ecology.

Another paper published this month in the journal New Phytologist is the study “Seasonal trends in the biomass and structure of bryophyte-associated fungal communities explored by 454 pyrosequencing”, authored by Davey et al., a group of researchers both members and affiliates of the Kauserud laboratory, and it is this paper I will address here.

Davey et al 2012 header

Bryophytes represent a portion of the dominant vegetation in boreal forests, but very little is understood about the taxonomy, seasonality, or biomass of the fungi associated with them.  Additionally, microbes associated with mosses may be responsible for nitrogen fixation and nutrient immobilization as epiphytes or on forest soils.  A previous study from the Kauserud lab reported high levels of fungal biomass and active plant cell wall degrading enzymes identified from moss-associated fungi.

Figure One

As I have mentioned here numerous times, fungi are notoriously hard to identify by cultural and morphological means and are extremely diverse.  To understand this diversity, the authors performed 454 pyrosequencing of the ITS2 region of the ribosomal DNA operon for molecular taxonomic identification against a database of known fungal sequences.  This sequencing was done in concert with an ergosterol HPLC assay that is used to estimate living fungal biomass.

Figure Two

The authors identified a large numbers of fungi, some presumably moss associated, and the total amount of fungi recognized was comparable to that found in forest soils.  The majority of fungi were identified as Ascomycetes, which agrees with other studies investigating vascular plant phyllosphere communities using the primer pair ITS3 and ITS4.  Additionally, this study identified a consistent taxonomic profile as a previous study from the Kauserud laboratory using a cloning strategy and Sanger sequencing approach.  Not surprisingly, this study reports orders of magnitude more fungi but identified roughly the same groups of fungi (Helotiales, Chaetothyriales, Agaricales, and Tremellales).

Figure Three

The researchers addressed seasonal variation by sampling every eight weeks between April and January over the course of a year.  Quite interestingly, there is a strong consensus in this study with other research that provides evidence that fungi not only survive under snowpack, but also continue to grow during the winter months.  While the researchers found consistent trends with regard to season, there were fluctuations in fungal biomass when considering host bryophyte.  By using principle component analyses, the authors show that the fungal communities are structured mainly by host plant and secondarily by the type of bryophyte tissue that was sampled.  This paper is an important contribution to the growing literature that show that plant-associated fungi are extremely diverse, dynamic, and show complex relationships with host plants.

One Hundred Important Questions Facing Plant Science Research

The October issue of the journal New Phytologist contains a commentary article by a group of plant scientists who conducted a survey to identify the 100 most pressing scientific questions facing plant biologists.  The article “One Hundred Important Questions Facing Plant Science Research” is very thought provoking.

I’ve replicated the questions here for you to read and ponder.  I know the list is heavy on the text, but I think these questions are worthy of the space.  You should definitely then read their article (and supplementary commentary) and see how they have collectively addressed these questions.  They may have addressed these questions in their commentary, but these questions are far from answered and may demand many careers to answer fully.

 Most important questions relating to plants and society:

1. How do we feed our children’s children?

2. Which crops must be grown and which sacrificed, to feed the billions?

3. When and how can we simultaneously deliver increased yields and reduce the environmental impact of agriculture?

4. What are the best ways to control invasive species including plants, pests and pathogens?

5. Considering two plants obtained for the same trait, one by genetic modification and one by traditional plant breeding techniques, are there differences between those two plants that justify special regulation?

6. How can plants contribute to solving the energy crisis and ameliorating global warming?

7. How do plants contribute to the ecosystem services upon which humanity depends?

8. What new scientific approaches will be central to plant biology in the 21st Century?

9. (a) How do we ensure that society appreciates the full importance of plants? (b) How can we attract the best young minds to plant science so that they can address Grand Challenges facing humanity such as climate change, food security, and fossil fuel replacement?

10. How do we ensure that sound science informs policy decisions?

11. How can we translate our knowledge of plant science into food security?

12. Which plants have the greatest potential for use as biofuels with the least effects on biodiversity, carbon footprints and food security?

13. Can crop production move away from being dependent on oil-based technologies?

14. How can we use plant science to prevent malnutrition?

15. How can we use knowledge of plants and their properties to improve human health?

16. How do plants and plant communities (morphology, color, fragrance, sound, taste etc.) affect human well-being?

17. How can we use plants and plant science to improve the urban environment?

18. How do we encourage and enable the interdisciplinarity that is necessary to achieve the UN’s Millennium Development Goals which address poverty and the environment?

 Most important questions relating to environment and adaptation:

1. How can we test if a trait is adaptive?

2. What is the role of epigenetic processes in modulating response to the environment during the life span of an individual?

3. Are there untapped potential benefits to developing perennial forms of currently annual crops?

4. Can we generate a step-change in C3crop yield through incorporation of a C4 or intermediate C3/C4 or crassulacean acid metabolism (CAM) mechanism?

5. How do plants regulate the proportions of storage reserves laid down in various plant parts?

6. What is the theoretical limit of productivity of crops and what are the major factors preventing this being realized?

7. What determines seed longevity and dormancy?

8. How can we control flowering time?

9. How do signaling and cross-talk between the different plant hormones operate?

10. Can we develop salt/heavy metal/drought-tolerant crops without creating invasive plants?

11. Can plants be better utilized for large-scale remediation and reclamation efforts on degraded and/or toxic land?

12. How can we translate our knowledge of plants and ecosystems into ‘clever farming’ practices?

13. Can alternatives to monoculture be found without compromising yields?

14. Can plants be bred to overcome dry land salinity or even reverse it?

15. Can we develop crops that are more resilient to climate fluctuation without yield loss?

16. Can we understand (explain and predict) the succession of plant species in any habitat, and crop varieties in any location, under climate change?

17. To what extent are the stress responses of cultivated plants appropriate for current and future environments?

18. Are endogenous plant adaption mechanisms enough to keep up with the pace of man-made environmental change?

19. How can we improve our cultivated plants to make better use of finite resources?

20. How do we grow plants in marginal environments without encouraging invasiveness?

21. How can we use the growing of crops to limit deserts spreading?

 Most important questions relating to plant species interactions:

1. What are the best ways to control invasive species including plants, pests and pathogens?

2. Can we provide a solution to intractable plant pest problems in order to meet increasingly stringent pesticide restrictions?

3. Is it desirable to eliminate all pests and diseases in cultivated plants?

4. What is the most sustainable way to control weeds?

5. How can we simultaneously eradicate hunger and conserve biodiversity?

6. How can we move nitrogen-fixing symbioses into non-legumes?

7. Why is symbiotic nitrogen fixation restricted to relatively few plant species?

8. How can the association of plants and mycorrhizal fungi be improved or extended towards better plant and ecosystem health?

9. How do plants communicate with each other?

10. How can we use our knowledge of the molecular biology of disease resistance to develop novel approaches to disease control?

11. What are the mechanisms for systemic acquired resistance to pathogens?

12. When a plant resists a pathogen, what stops the pathogen growing?

13. How do pathogens overcome plant disease resistance, and is it inevitable?

14. What are the molecular mechanisms for uptake and transport of nutrients?

15. Can we use non-host resistance to deliver more durable resistance in plants?

Most important questions relating to the understanding and utilization of plant cells:

1. How do plant cells maintain totipotency and how can we use this knowledge to improve tissue culture and regeneration?

2. How are growth and division of individual cells coordinated to form genetically programmed structures with specific shapes, sizes and compositions?

3. How do different genomes in the plant talk to one another to maintain the appropriate complement of organelles?

4. How and why did multicellularity evolve in plants?

5. How can we improve our understanding of programmed developmental gene regulation from a genome sequence?

6. How do plants integrate multiple environmental signals and respond?

7. How do plants store information on past environmental and developmental events?

8. To what extent do epigenetic changes affect heritable characteristics of plants?

9. Why are there millions of short RNAs in plants and what do they do?

10. What is the array of plant protein structures?

11. How do plant cells detect their location in the organism and develop accordingly?

12. How do plant cells restrict signaling and response to specific regions of the cell?

13. Is there a cell wall integrity surveillance system in plants?

14. How are plant cell walls assembled, and how are their strength and composition determined?

15. Can we usefully implant new synthetic biological modules in plants?

16. To what extent can plant biology become predictive?

17. What is the molecular/biochemical basis of heterosis?

18. How do we achieve high-frequency targeted homologous recombination in plants?

19. What factors control the frequency and distribution of genetic crossovers during meiosis?

20. How can we use our knowledge about photosynthesis and its optimization to better harness the energy of the sun?

21. Can we improve algae to better capture CO2and produce higher yields of oil or hydrogen for fuel?

22. How can we use our knowledge of carbon fixation at the biochemical, physiological and ecological levels to address the rising concentrations of atmospheric CO2?

23. What is the function of the phenomenal breadth of secondary metabolites?

24. How can we use plants as the chemical factories of the future?

25. How do we translate our knowledge of plant cell walls to produce food, fuel and fibre more efficiently and sustainably?

 Most important questions relating to plant diversity:

1. How much do we know about plant diversity?

2. How can we better exploit a more complete understanding of plant diversity?

3. Can we increase crop productivity without harming biodiversity?

4. Can we define objective criteria to determine when and where intensive or extensive farming practices are appropriate?

5. How do plants contribute to ecosystem services?

6. How can we ensure the long-term availability of genetic diversity within socio-economically valuable gene pools?

7. How do specific genetic differences result in the diverse phenotypes of different plant species? That is, why is an oak tree an oak tree and a wheat plant a wheat plant?

8. Which genomes should we sequence and how can we best extract meaning from the sequences?

9. What is the significance of variation in genome size?

10. What is the molecular and cellular basis of plants’ longevity and can plant life spans be manipulated?

11. Why is the range of life spans in the plant kingdom so much greater than in animals?

12. What is a plant species?

13. Why are some clades of plants more species-rich than others?

14. What is the answer to Darwin’s ‘abominable mystery’ of the rapid rise and diversification of angiosperms?

15. How has polyploidy contributed to the evolutionary success of flowering plants?

16. What are the closest fossil relatives of the flowering plants?

17. How do we best conserve phylogenetic diversity in order to maintain evolutionary potential?

Potato Genome Sequence and Analysis

With next-generation sequencing technologies dropping in price and increasing in throughput, it’s not surprising to find multiple genomes published every week in scientific journals.  Most of these articles don’t qualify for publication in the top tier of journals like they did at the onset of the next-generation sequencing boom, but some genome sequencing projects, such as the potato genome, are high profile enough to warrant publication in top tier journals.

In the July 14th issue of the journal Nature, a draft of the potato (Solanum tuberosum) genome was described in a paper authored by the Potato Genome Sequencing Consortium – a huge group of researchers from 26 institutions.

The potato is the world’s fourth most consumed food crop, the most commonly grown vegetable crop, and a member of the economically important Solanaceae family –otherwise known as the nightshades – which include tomato, peppers, aubergine (eggplant if you live in the United States), tobacco, and petunia.  Widely distributed in western South America, tuber forming Solanum species are highly morphologically diverse and easily cross with other varieties for breeding purposes.

It’s been a bumpy road sequencing the potato genome since the project was started in 2006.  The potato genome is an extremely heterozygous autotetraploid, which translates to four highly variable copies of each of the 12 chromosomes.  It’s also the first sequenced Eudicot genome in the Asterid clade, so there are no close genetic relatives to provide the basis for a guided genome assembly.

The consortium began the sequencing by creating a bacterial artificial chromosome (BAC) library of 78,000 clones from a well studied diploid line providing high quality potatoes, named RH89-039-16.  The group used the BAC library and 10,000 AFLP markers to create more than 7000 contigs which were constructed into a physical map.  The group then identified up to 150 BACs for every chromosome on the potato genome, and verified their locations using fluorescent in situ hybridization.

Heterozygosity was so high in the RH line that after thorough sequencing the group hit an impasse with the assembly of the genome.  In an attempt to complement the sequencing of the RH line, the consortium began sequencing a doubled monoploid potato clone, DM1-3 516R44, derived from a diploid wild South America accession.  The DM line has a simpler genome than the RH line and is highly homozygous.

Using both the Illumina Genome Analyzer II and Roche 454 pyrosequencing platforms, and supplementing this data with traditional Sanger sequencing, approximately 96 Gb of data was acquired for the DM line.  The group then used the SOAPdenovo computer program to assemble the reads with a final assembly of 727 Mb for the DM line and a final estimation of 844 Mb for the genome.

The consortium generated more than 31 Gb of transcriptome data from both the DM and RH line libraries.  These 48 libraries represented major tissue types, developmental stages, and included various responses to abiotic and biotic stresses.  All the reads from the RNA-Seq libraries were mapped to the assembled DM genome.  Using gene prediction methods, along with protein and EST data, the potato genome was predicted to contain 39,000 protein coding genes, an amount which is in agreement with other plant genomes.  Within these genes, there were an estimated 2,642 asterid-specific and 3,372 potato-lineage-specific genes.  Some of the predicted asterid-specific genes include many novel transcription factors, self-incompatibility factors, and defence-related proteins. The draft assembly of the genome consists of more than 60% repeated elements.  The largest class of the transposable elements is the long terminal repeat retrotransposons (LTRs) which are estimated at 30% of the potato genome.

The potato is notorious for being susceptible to many pathogens and pests.  This well known susceptibility was one of the priorities for sequencing the genome and determining genes responsible for disease resistance and pathogen defense.  The DM genome assembly contains more than 800 putative R genes, responsible for conferring disease resistance, including 408 NBS-LRR-encoding genes, 57 Toll/interleukin-1 receptor (TIR) domains, and 351 non-TIR type resistance genes.  An extreme number of pseudogenes – attributed to indels, frameshift mutations, and misplaced stop codons –were identified within known R gene motifs, which possibly explains the potato’s inability to fight off some specific diseases.

One such well known disease, Late Blight, caused by Phytophthora infestans, was responsible for the Irish Potato Famine in the 1840s..  Using information from this genome sequencing project and other studies, we now know the variety brought to Europe in the late 16th century happens to lack specific disease resistance genes for Phytophthora infestans.  One could speculate that unbridled transposon jumping caused the inactivation of many R genes in this potato variety.

Unique for the potato is the formation of tubers (the actual potatoes) through the modification of a stolon.  The tomato is very closely related to potato, but does not produce stolons or modified tubers.  The group used transcript data from both potato and tomato to address genetic regulation of the formation of stolons and the transition of stolons to tubers.  Quite interestingly, the formation of stolons and tubers coincides with an up-regulation of genes associated with starch biosynthesis, protein storage, and Kunitz protease inhibitor genes associated with pests and pathogens.

Possibly due to extremely high levels of heterozygosity, it has been difficult to improve the potato through traditional breeding efforts.  It’s estimated that there is a worldwide economic loss of 4.5 billion US dollars to potato crops from diseases each year.  Just to attempt to suppress these diseases copious amounts of pesticides and fungicides are applied to potato crop land each year.  The potato cyst nematode, for example, is an important pest that researchers hope to improve resistance to via breeding initiatives.  Having this draft potato genome sequence will aid in the characterization of existing germplasm collections and description of allelic variance in breeding efforts to avoid diseases.  The potato genome will also serve as a resource for breeders wanting to improve the quality of other economically important Solanaceous plants such as tomato, pepper, eggplant, and tobacco.

Jacques Monod Conference: Integrative Ecological Genomics

Ecological genomics is thriving as a discipline, evidenced by the number of research papers published in this area, and this is due to the large amounts of genomic data now available to researchers.  Information from individual genomes, “pan-genomes”, and large scale environmental genome sequencing is giving us a more complete picture of biological diversity.

Some of the top researchers in this newly emerging discipline will be speaking at the Jacques Monod Conference “Integrative Ecological Genomics.”  The meeting is held in Roscoff, Brittany, France.  Registration is by application (the submission deadline is June 20th 2011) and the number of attendees is capped at 115 people.  Information regarding the meeting and registration can be found here and here.

XV International Congress on Molecular Plant-Microbe Interactions

The XV International Congress on Molecular Plant-Microbe Interactions has shaped up to be an amazing meeting.  A stellar group of researchers will be presenting at the meeting.  Registration is open now.

Directly from the meeting website:  “The XV International Congress on Molecular Plant-Microbe Interactions is recognized as the most important international meeting for plant-microbe interactions to discuss research and network with colleagues from around the world.  This meeting is the global venue for presenting and discussing new research and developments in molecular plant-microbe interactions.  Through plenary lectures, concurrent sessions, special workshops and various events, attendees experience innovative plant-microbe interactions research.  The meeting features hundreds of abstracts and provides networking and professional development opportunities.”