Making waves at the Plant Calcium Signalling Meeting

Calcium ions (Ca2+) are important signal molecules to relay information around, and between cells. In plants, calcium signals are involved in many processes including cell growth, environmental stress (e.g. high salt in soil) responses, and defence against disease-causing microbes. Last week, many of the researchers studying calcium signals in plants gathered together at the Plant Calcium Signalling 2014 meeting in Münster, Germany.

Main administration building of WWU Münster.

Main administration building of WWU Münster. Photo by Rüdiger Wölk / Wikipedia.

I really enjoyed the meeting. It was great to hear about the current research being undertaken by others, and to see how much the research area has moved forward since the previous meeting was held in 2010. Lots of exciting research was presented at the conference, but I’m just going to mention a few of my favourites.

Long-distance calcium waves in plant roots were discussed from the perspective of a biologist (Simon Gilroy, University of Wisconsin), and then a physicist (Matthew J Evans, John Innes Centre). Gilroy’s research group found that treating plant roots with salt (NaCl) activates rapid calcium (Ca2+) waves that travel at speeds of around 400 µm/s from root to shoot (1). High salt levels can be harmful to plants and the calcium wave is likely to be involved in activation of whole-plant stress responses that help the plant survive in these conditions. In the video below the wave is visible as a colour change from yellow (low calcium ion levels) to red (high calcium ion levels).

Evans then presented the mathematical model he is developing based on Gilroy’s biological data. Although the model is a simplification of what would be happening in a plant, it matches the current biological data pretty well. Using the model, it is possible to make predictions that Gilroy’s research group can now test in plants.

Calcium signals are sensed by calcium-binding proteins that then activate/inactivate downstream responses in cells. There are loads of calcium-binding proteins in plants, grouped into several types. Why plants need so many calcium-binding proteins is a bit of a mystery. At the meeting, Jürg Kudla (WWU Münster, Germany) presented data that may help to answer this question. He found that two calcium-binding proteins from different families act synergistically to activate a downstream cell response. Although both proteins could activate the response on their own, a much higher level of activation was achieved when both were present.

Researchers have access to several tools to visualise calcium signals in cells. Melanie Krebs (University of Heidelberg) discussed her work adapting the GECO calcium sensors, which were first developed for use in animal cells (2), for expression in various locations within plant cells. The GECOs are more sensitive than other calcium reporters such as Cameleon YC3.6. Krebs demonstrated that they could be used to visualise some calcium changes in individual cells that have only previously been observed at the whole plant/organ level.

My two other favourite talks were about the roles of calcium in plant development. José Feijo (University of Maryland) discussed the role of calcium in pollen tube growth during fertilisation. Straight after, Alex Webb (University of Cambridge) presented his research on the role of calcium in the circadian clock, which is the internal clock plants have to co-ordinate their growth and metabolism with the day-night cycle. Alongside all the talks, the conference had poster sessions where researchers could discuss their work on a more informal basis.

The meeting was a really useful opportunity for the plant calcium signalling research community to get together and I would like to thank the organising committee for all the hard work they put into running it.

References

1) Choi et al (2014) Salt stress-induced Ca2+ waves are associated with rapid, long-distance root-to-shoot signalling in plants. PNAS. PMID: 24706854
2) Zhao et al (2013) An Expanded Palette of Genetically Encoded Ca2+ Indicators. PubMed Central. PMID: 21903779

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A day in the life…

Image: Wikimedia Commons.

Image: Wikimedia Commons.

Well, dissident Russian novelist Alexander Solzhenitsyn did it (with Ivan Denisovich), that Swinging Sixties phenomenon, the mop-topped beat combo that is The Beatles did it with typical inventivenesss and musicality – and probably a ‘little help from their friends’* – and now labs are getting in on the act. Welcome to The Node’s ‘a day in the life of a …’ seriesThe Node was launched in June 2010 by Development, a leading research journal in the field of developmental biology, and its publisher, The Company of Biologists, as a non-commercial information resource and community site for the developmental biology community, and ‘a place to share news about and with the developmental biology [which includes plant and non-plant-based work… – Ed.] community around the world’. Designed to give insights into the working of the labs – and the people – that try to unravel development, it has already showcased Narender Kumar, graduate student, in an arabidopsis lab at Louisiana State University (USA), and Dr James Lloyd in a moss lab at the University of Leeds (UK). I’d like to think that these insights into the more human sides of plant development research might help to inspire the next generation to get involved in plant biology research and rise to the challenges of the 21st century that so often revolve around food and energy security – solutions to both of which conundra will have important botanical dimensions.

* The Rolling Stone magazine voted the Beatles’ A day in the life to be that group’s best song, and the 28th best song of all time.

[And if you’d like to read more about plants in the lab., check out the University of Bristol’s School of Chemistry’s ‘Plants in the Lab’ website, which ‘by bringing beautiful and interesting plants and flowers into the laboratory setting and then explaining what some of the molecules produced naturally mean to chemists, we are hoping to challenge the familiar divide between nature and laboratory’. Talking of Bristol University, who’s our favourite Trollope-loving botanist? Melville Wills Professor of Botany Alistair Hetherington (whose botanical life story is told in Current Biology.) And for the day when you have to leave the lab – maybe to go to another one..? – Natalie Butterfield has the ‘perfect lab leaving list’ for you. – Ed.]

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Flow cytometric analysis of bee pollen loads

Flow cytometric analysis of bee pollen loads

Flow cytometric analysis of bee pollen loads

Understanding the species composition of pollen on pollinators has applications in agriculture, conservation and evolutionary biology, but current identification methods cannot always discriminate taxa at the species level. Kron et al. test the use of flow cytometry to characterize pollen loads from individual bees, using DNA content as a species marker, and find that they are able to quickly measure DNA contents for nuclei from hundreds to thousands of pollen grains per bee. They observe differences in pollen load diversity between bumble-bees and honey-bees and find evidence of between-cytotype pollinator movement in a population of Solidago. This technique provides a new tool to complement other methods for examining pollinator behaviour.

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Regulation of root morphogenesis in arbuscular mycorrhizae (Review)

Regulation of root morphogenesis in arbuscular mycorrhizae (Review)

Regulation of root morphogenesis in arbuscular mycorrhizae (Review)

Increased root branching is recognized as a general feature of arbuscular mycorrhizal (AM) roots, but a full understanding of the mechanisms involved is still lacking. Fusconi reviews the subject and concludes that fungal exudates are probably the main compounds regulating AM root morphogenesis during the first colonization steps, while a complex network of interactions governs root development in established AMs. The possible involvements of phosphate, which generally increases in AM plants, and of variations in sugar transport and in hormone homeostasis, signalling and interactions are also discussed.

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Impact of climate on plant growth and flower formation – This Week in Annals of Botany

Xylem Impact of warming and drought on carbon balance related to wood formation in black spruce
Wood formation in trees represents a carbon sink that can be modified in the case of stress. The way carbon metabolism constrains growth during stress periods (high temperature and water deficit) is now under debate. In this study, the amounts of non-structural carbohydrates for xylogenesis in black spruce saplings were assessed under high temperature and drought in order to determine the role of sugar mobilization for osmotic purposes and its consequences for secondary growth. Plant water status during wood formation can influence the materials available for growth in the cambium and xylem.

 

Relative growth rate variation of evergreen and deciduous savanna tree species is driven by different traits
Plant relative growth rate depends on biomass allocation to leaves (leaf mass fraction, efficient construction of leaf surface area (specific leaf area) and biomass growth per unit leaf area (net assimilation rate). This paper shows that trade-offs between investment in carbohydrate reserves and growth occur only among deciduous species, leading to differences in relative contribution made by the underlying components of relative growth rate between the leaf habit groups. The results suggest that differences in drivers of relative growth rate occur among savanna species because these have different selected strategies for coping with fire disturbance in savannas.

 

DEF- and GLO-like proteins may have lost most of their interaction partners during angiosperm evolution
DEFICIENS (DEF)- and GLOBOSA (GLO)-like proteins constitute two groups of floral homeotic transcription factors that were already present in the most recent common ancestor of angiosperms. Together they specify the identity of petals and stamens in flowering plants. This paper strengthens the hypothesis that a reduction in the number of interaction partners of DEF- and GLO-like proteins, with DEF–GLO heterodimers remaining the only DNA-binding dimers in core eudicots, contributing to developmental robustness, canalization of flower development and the diversification of angiosperms.

 

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What inspired you to do plant science? #epso2014

This week guest author Charlie Haynes is AoB Blog’s roving reporter at the EPSO/FESPB plant biology Europe conference.

At the FESPB/EPSO plant biology conference in Dublin I asked some of the delegates what inspired them to work in plant science, botany and ecology. Here are just a few of their answers:

 

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Seed dormancy cycling in a halophytic shrub

Seed dormancy cycling in a halophytic shrub

Seed dormancy cycling in a halophytic shrub

Soil seed banks and dormancy cycling have been well studied in annuals, but less is known about woody plants. Cao et al. investigate the cold desert shrub Kalidium gracile (Amaranthaceae) and find that it has three life history traits that help ensure persistence at a site: a polycarpic perennial life cycle, a persistent seed bank and dormancy cycling. Buried seeds exhibit an annual non-dormancy/conditional dormancy cycle, and germination varies in sensitivity to salinity during the cycle. Dormancy cycling is co-ordinated with seasonal environmental conditions in such a way that the seeds germinate in summer, when there is sufficient precipitation for seedling establishment.

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AoB Interviews: Hans Lambers on soil phosphate acquisition in impoverished soil

This week guest author Charlie Haynes is AoB Blog’s roving reporter at the EPSO/FESPB plant biology Europe conference.

 

Hans Lambers Hans Lambers is the Winthrop Professor at the University of Western Australia. He competed his PhD in 1979 at the University of Groningen in the Netherlands and since then worked at Melbourne University, Australian National University and Utrecht University. His research focuses on mineral nutrition of native Australian plants and crop and pasture legumes. He very kindly agreed to talk to me about some of the challenges of soil phosphate impoverishment.

Why is phosphate impoverishment so significant?
It’s of less importance in Europe which imports food and animal feed from parts of the world where phosphates passing the problem on. There it is an issue of excess of phosphate, dumped on the land and ending up in waterways. Europe could stop fertilising now and still have crops for the next 20 years. But when you go to other parts of the world; Australia, South America, Africa and South East Asia, phosphate insecurity is a real issue. This may be because the amount in the soil is too low for effective crop production, or it may be that it is there but it’s not readily available. So it’s an issue for crop production and thus food security. What we can do though is instead grow plants that can use that phosphorus in the soil much more effectively. There is a tremendous opportunity.

How does this limit these countries in what they can grow and the yields they can produce?
In Africa phosphorus is the key limiting factor, even some the driest areas of Saharan Africa. People who worked in barchenener discovered that simply by adding phosphorus you could get a higher yield. The dry soil significantly reduces the mobility of phosphorus in the soil and it becomes a significant limiting when you have a dry soil (Lambers H, Raven JA, Shaver GR, Smith SE. (2008) Plant nutrient-acquisition strategies change with soil age. Trends in Ecology and Evolution 23: 95-103).

So why do these communities not buy fertiliser to increase their yield?
Fertiliser is very expensive for these groups. It has to travel vast distances to the harvest, and these groups simply don’t have the money for it. So there instead we are working towards crops that are more efficient at using the existing phosphorus or are better at getting it out of the soil. This is however a bit of a risky business – if you have soils that are very nutrient poor to begin with then plants that extract it more effectively will make the soil even more phosphorus deficient. Whatever you take out of soil have to replace in order to be sustainable.

What makes phosphates accessible?
Phosphates in soil are readily available at a neutral pH. Calcareous soils with their more alkali pH lock phosphates up in calcium complexes. The phosphate is there but not readily available to crops. More acidic soils also lock up phosphates – but this time not in calcium complexes but instead, as complexes of oxides and hydroxides of iron and aluminium. Chile has very acidic soil, with a pH of almost 4, and lots of these metal oxides and hydroxides so all the phosphate isn’t readily available. However the plants have special adaptations that allow them to access it in these conditions.

What are these adaptions?
These plants have a special structure which works in combination with the plant biochemistry. What they produce is massive quantities of carboxylates. These are molecules with a negative charge – like phosphate. These exchange for one another, releasing the phosphate ions into the soil solution, whilst carboxylates anion take the place of phosphate in the soil. You’re effectively mining the phosphate that is in the soil out of it’s tight bindings. It’s then in the solution and anybody can take it up (Lambers H, Bishop JG, Hopper SD, Laliberté E, Zúñiga-Feest A. (2012) Phosphorus-mobilization ecosystem engineering: the roles of cluster roots and carboxylate exudation in young P-limited ecosystems. Annals of Botany 110: 329-348).

Could this be put into another crop either by breeding or genetic modification?
I would take one step back and ask ‘what crops do we have now at already can do that’? White Lupin is an excellent example and there are a few other Lupin species that do exactly the same. There are also some Lupin species that don’t have these wonderful structures but instead something close to it, and some without a structure at all that still release carboxylates. So we actually already have a lot of species that can already played this trick. Rather than engineer this in Soybean, it’s important to get a thorough understanding of the technology. Understanding is and farming it in crops with the gene is an obvious first stage. We already have crops with the this ability in lupins – which are much better than wheat and barley at this stage. I don’t think it’s impossible but it’s important to take it one step at a time (Lambers H, Clements JC, Nelson MN. (2013) How a phosphorus-acquisition strategy based on carboxylate exudation powers the success and agronomic potential of lupines (Lupinus, Fabaceae). American Journal of Botany 100: 263-288).

So are some parts of the world focusing on the wrong crops for their soil type and climate?
Yes absolutely! In chile they used to grow Andean Lupin. When the Spanish invaded they forbade the natives from growing these lupins as they weren’t Spanish crops. The natives switching to foreign crops is a daft idea when they already had a crop suited to their environment! Quinoa is an example of another crop where this happened, and the Spanish stopped that. They arguably had better crops than the foreign spanish ones then introduced. One thing one can do though is intercropping. This is where you grow plants concurrently interspersed between one another. If you want to grow wheat, it cannot grow particularly well in some South American environments. If you intercrop it with Lupin, can mobilise that phosphorus and the neighbours can benefit from that. You can also do crop rotation. A group in Germany has actually done this, working with rotations of soybean and maize. Maize is not so good at accessing phosphate, soybean – depending on the cultivar you use, is. The good soybean cultivars show a real benefit for the next crop – a phosphorus benefit. You can grow them at the same time or you can grow them in rotation to access this phosphate. Both of these techniques have tremendous benefits.

What stops people in phosphorus poor environments from doing this already?
That’s an interesting question. If you go to china, intercropping has been done for hundreds of years and you can demonstrate that with the right intercropping combinations you can have a 40-50% higher yield – which is pretty impressive! A British or Irish farmer with an increase in yield of that kind of level would be ecstatic! So the Chinese already have done that, and Europe is exploring it. I’m certain it could be done in other parts of the world, but it’s not happening on a large scale and that’s because a lack of education. It’s important to educate local farmers about this from Africa to Australia! I’m working with a group in Germany Andreas Burgutts, who is screening sorghums for better phosphate accessibility, using leaf manganese levels as a marker. These are taken up by the plant in the same as as phosphates and so used as a marker. Work like this requires going to Africa, and selecting the right cultivar for the conditions there, not in our lab field. This is about doing research and then making use this research reaches farmers, and doesn’t stay in a scientist’s ivory tower. Work needs to be done and go beyond journals, into places where we can make a difference,

Who else is working on taking this knowledge into the field?
I had a visit from someone from ICRISAT. They are based in India and work on major crop draught and salinity. They are now keen to work on phosphorus, and they had heard of my work and were interested in developing something together. These big international institutes have the links with the grassroots farming communities in the parts of the world where you can truly make a difference. I may be able to do high end science but without the connections I’m not able to have much of a real world impact.

Who else is involved?
The big international institutes are doing good work, IRRI in the Philippines, ICARDA in Aleppo and ICRISAT in Hyderabad. These large international institutes aren’t just interested in the science, but also applying it, and I think that is really important.

Do these plants have potential in any other key areas?
Yes, for instance where you have soil contaminated with heavy metals you could use them in the process of photoremediation. Here plants as used for their ability to remove heavy metals an ‘clean’ soil. There are areas in Belgium that have been heavily polluted with zinc or copper. Chemical or physical cleaning of this soil is almost impossible. You need a species that accumulates these metals to a very high concentration, but is also a fast grower, producing a lot of biomass, or else the process takes along time. There is serious potential in this. In addition to this these plants can be used in phytomining or prospecting, accumulating small amounts of metals that act as an indicator for a larger deposit of metal in the earth. This can act as a pretty good indicator of gold and some other metals to allow groups to commence mining.
Hans’ book “Plant Life on the Sandplains in Southwest Australia, a Global Biodiversity Hotspot” will be out in September, and is now available online at the UWA Publishing website.

 

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