Climate change and seed dormancy in tropical areas: an ecological and genetic perspective. Henk W.M. Hilhorst Wageningen Seed Lab Lab. of Plant Physiology Wageningen University The Netherlands
The world is getting warmer... www.dreamatico.com
www.theguardian.com
www.zilient.org...and drier
Water level in the Jaguari reservoir in Sao Paulo, Brazil, following the 2014 drought. August 2013
Water level in the Jaguari reservoir in Sao Paulo, Brazil, following the 2014 drought. August 2014
Loss of arable land in the coming decades
Predicted drought until the end of the century
Growing coffee in Siberia?
Brazil: The world's top coffee producer Intergovernmental Panel on Climate Change (IPCC) A 3ºC rise in temperature and a 15% decrease in rainfall from pre-industrial levels in Minas Gerais and Sao Paulo, could reduce the potential area for coffee production from 70-75% to 20-25%.
How does seed performance change in a changing climate and, if so, what are the consequences?
For wild seeds? Biodiversity at stake? For crop seeds? Food security at stake? www.motherearthnews.com www.seedgrower.bayer.com
The occurrence of dormancy throughout climate zones of the world
How does the environment influence seed dormancy (and seed quality?) 1. Prevailing environment 2. Parental environment 3. Prevailing X Parental environment
Very complex interactions Walck et al., Global Change Biology 2011
The soil seed bank Timing of emergence is determined by flowering time and dormancy http://wric.ucdavis.edu/
Example Physical dormancy http://saseedbank.com.au/ Wikipedia Acacia suaveolens Dillwynia floribunda
After-ripening Example Physiological dormancy Summer conditions Spring conditions
Longer after-ripening period before rainfall favours species with lower temperature optima for germination now predicted Walck et al., Global Change Biology 2011
Requirement for cold/warm stratification to break dormancy Plasticity of response Duration of cold period Walck et al., Global Change Biology 2011
Shifts of germination phenology of seeds requiring cold stratification now future future now shortened winters: partial dormancy break premature spring warm-up accelerates germination. Walck et al., Global Change Biology 2011
Dormancy cycling: The depth of dormancy is continually changing through induction and relief in response to a range of environmental signals. Arabidopsis (Cvi) Germination Temperature (%) ( C) 25 100 20 80 15 60 10 40 5 20 5 C 10 C 15 C 20 C 25 C 50 200 40 150 30 100 20 50 10 Days after-ripening, post-exhumation Soil moisture content (%) to 50% germination (AR50) Suitable time of year 0 0 Oct-07 Dec-07 Feb-08 Apr-08 Jun-08 Aug-08 Oct-08 Oct-07 Dec-07 Feb-08 Apr-08 Jun-08 Aug-08 Oct-08 Exhumation date Temporal signals Suitable conditions for germination Spatial signals 0 0 e.g. Temperature e.g. Light, Nitrate Environmental signals remove successive layers of dormancy to complete germination at an optimum time Footitt et al, 2013. Plant J. 74:1003-1015
What are the molecular mechanisms of dormancy cycling and how are these regulated by environmental factors? We re only scratching the surface, but
DELAY OF GERMINATION 2D Graph 3 25 Summer annual DOG1 relative expression 2.0 1.5 1.0 0.5 DOG1 Soil temperature 20 15 10 5 Soil temperature at 5cm (oc) Cvi 0.0 0 Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Calender Time 5000 25 Depth of dormancy (sensitivity to spatial signals) Winter annual DOG1 relative expression 4000 3000 2000 1000 20 15 10 5 0 Soil temperature at 5cm ( C) Bur 0 Oct/09 Dec/09 Feb/10 Apr/10 Jun/10 Aug/10 Oct/10-5 Calender time DOG1 expression is highly negatively related to soil temperature in both Cvi and Bur, but dormancy patterns differ.
DELAY OF GERMINATION1 80 0.8 ABA ng g -1 DW 70 60 50 40 30 20 DOG1 ABA ng/g 0.6 0.4 0.2 DOG1 Relative Expression 10 0 0 50 100 150 200 0.0 Depth of dormancy. Days to AR50 DOG1 is a thermal sensing mechanism setting dormancy level via altered sensitivity to background ABA in different ecotypes. Footitt et al, 2013. Plant J. 74:1003-1015
Sensitivity to spatial environmental signals changes and when this coincides with a suitable environment seed germination is completed Temporal signals Spatial signals Footitt et al, 2013. Plant J. 74:1003-1015 Finch-Savage and Footitt, 2017. J Expt Bot 68:843-856
Nitrate content Light quality Seasonal temperatures determine overlap of germination window with field temperature, light- and nitrate thresholds 40 Max Field temperature, C 30 20 10 [nitrate] P fr /P tot T field Min 0 Oct Jan Apr Jul Oct Time Hilhorst, 2007
A schematic model of dormancy cycling and germination timing LIGHT Ambient TEMPERATURE NITRATE Ambient Output: DOG1 + other factors Increasing sensitivity GA Sensitivity ABA Increasing sensitivity Output: GA-synthesis (GA3ox1) GA/ABA-signaling Output: ABA degradation (CYP707A2) Dormancy relief Dormancy induction Dormancy cycling Finch-Savage and Footitt, 2017. J Expt Bot 68; 843-856
Conclusions on seed ecology and climate change Seeds respond to many environmental signals
Conclusions on seed ecology and climate change - Extremely complex: multiple interactions - Plant plasticity - Plant adaptability - Prediction per species, per climate zone - Seed bank dynamics: after-ripening/stratification
Parental Environment heathermccorkle.blogspot.com
Parental environment x plant development (= seed quality) N P K www.pioneer.com
The effects of the parent environment on seed germinability (Seed Science Research, 1991) M. Fenner a1 a1 Biology Department, Southampton University, Southampton SO9 5NH, UK Abstract. This has been demonstrated in numerous species, both wild and cultivated. The evidence comes from field observations and controlled experiments. A survey of the literature shows that some well defined patterns emerge, with certain environmental factors tending to have similar effects over a wide range of species. The effects are probably the result of changes in the quantity, mobility or activity of growth substances such as abscisic acid. The ecological implications of the phenomenon are briefly discussed.
Temperature Arabidopsis thaliana grown at 3 temperatures 20 C 15 C 10 C Kendall S L et al. Plant Cell 2011;23:2568-2580
Temperature of the parental environment is the most dominant factor determining seed performance Principle component analysis of 124 metabolites of seeds produced at: High light Low light Low temperature Low nitrate He et al., 2014
Networks of metabolites Carbon 20 C Nitrogen 15 C
(Maternal) temperature perception and signal transduction ICE1 HOS1 Modified from Kendall S L et al. Plant Cell 2011;23:2568-2580 PATENT: WO 2013190322 A1
The hos1 mutant is insensitive to maternal temperature PATENT: WO 2013190322 A1
Environmental factors play a dual role Parental Prevailing He et al., 2013
A case study: High temperature + drought: The green seed problem in soybean yellow green
Normal conditions Chlorophyll is completely degraded during maturation
Causes of Chlorophyll Retention High temperatures Drought + Genetic Components Severe rust Drying temperature nd nd nd = not detected
Consequences of Chlorophyll Retention Chlorophyll retention = lower seed quality Viability Vigor Longevity Grade standards for acceptable green seed percentage: Brazil = 8% USA = 1% Dark-colored oil Rancidity
Presence of chlorophyll in seeds = lower seed quality www.corn.agronomy.wisc.edu/
Chlorophyll vs Seed Quality Lot 74,5 % green seeds 110 lots Green seeds Yellow seeds Green seeds Photos: Daiani Ajala Luccas
Oil quality MINISTÉRIO DA AGRICULTURA, PECUÁRIA E ABASTECIMENTO IN Nº 49, of DECEMBER 22, 2006 (BRASIL, 2006): define the characteristics of identity and quality of refined vegetable oils. Sensory characteristics, color, impurities, composition of fatty acids, stability index, peroxide index, unsaponifiable matter, smoke point, etc... IN Nº 11, of MAY 15, 2007 (BRASIL, 2007): establish the Soybean Technical Regulation. Green Seed In-natura consumption: up to 4% Other uses: up to 8%
Presence of chlorophyll in seeds = lower oil quality Green Seeds: Reduction of up to 3% of the total amount of oil Higher acidity Higher refining cost Lower quality in storage light - oxidation Oxidation of the oil is influenced by the composition of fatty acids, oil processing, light, temperature, concentration and type of oxygen, free fatty acids, mono and diacylglycerols, transition metals, peroxides, thermally oxidized compounds, pigments and antioxidants.
Chlorophyll (mg/kg) Oxidative Stability 110 C (h) Example: Cultivar W799 Tocopherols and Tocotrienols (mg/100g) 67.44 118.49 8.57 8.66 4.28 0.14 Green Seeds Yellow Seeds Green Seeds Yellow Seeds
How to address the green seed problem?
Some research questions 1. Does chlorophyll directly affect soybean seed quality? Or is it just a marker for the stage of seed ripening? 2. Why do seeds have chlorophyll, if it is potentially damaging? Biological role? 3. Can we dissect the environmental from the genetic causes of green seeds?
Approaching the Green Seed Problem STEP 4 Molecular markers for breeding/genes for genetic modification STEP 1 Chlorophyll vs seed/oil quality STEP 3 Molecular control of chlorophyll degradation STEP 2 Molecular characterization of chlorophyll retention
Collaborators José França Neto Fernando Henning Lilian Henning Silvana Marin Francisco C. Krzyzanowski Edvaldo A Amaral da Silva Henk WM Hilhorst
Learning from seeds: How to counteract damage from drought?
In orthodox seeds drying is integrated in their normal development and, thus, they are desiccation tolerant
Xerophyta viscosa: a seed in plant s clothing? A resurrection plant
Xerophyta viscosa rehydration
Transcriptomics of dehydration/rehydration cycle of mature X. viscosa leaves
Co-expression networks during dehydration of mature X. viscosa leaves. Seed-specific ABI3 regulon Monke et al. (2012 ) Nucleic Acids Res. 40: 8240-54.
The DT switch + drought Reintroduction of vegetative DT in desiccation sensitive crops
Final conclusions
Greatest challenge for the future: Design new crops (and seeds!) that are adapted to climate change Plant breeding climate smart agriculture Integrated molecular-genetics and genomics CRISPR-Cas9 for gene/genome editing Biologicals and chemical stimulants
Thank you for your attention! www.wageningenseedlab.nl