9/25/2014

Salt-tolerance mechanisms in halophytes

Diana Katschnig, Henk Schat, Jelte Rozema

Most crops species are salt sensitive

 Less than 50 mM NaCL in salt-sensitive crops enough to reduce yield by 50%

Seawater salinity: Maas and Hoffman 1977 ~ 500 mM NaCl ~ 50 Ds/m = Ms/cm ~ 1700 mg Cl-/L

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Plants growing on saline soils face several challenges

1. Water uptake is hampered because of Cl- the ψs of the soil Na+ Na+ 2. Salts accumulate Cl- within the plant to Na+ - toxic levels Cl 3. Deficiencies of essential nutrients Na+ + Na+ X X occur, e.g. K Cl- Cl- - + + Cl Cl- Na Na K+

Salt tolerance is a complex trait Leaf cell +  Accumulation and Na Cl- compartmentation of ions

 Synthesis of compatible Cl- + solutes Na Na+ Cl-  Regulation of the salt Na+ concentration in the Cl- transpiration stream

 Uptake of essential + nutrients Na+ Na Cl- Cl- - + + Cl Cl- Na Na K+

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Halophytes

‘Plants capable of completion of their life cycles in a salt concentration of at least 200 mM NaCl (~40 % seawater) under conditions similar to those that might be encountered in the natural environment’

Flowers and Colmer (2008) New Phytologist

Halophytes

• Only <1% of all plant species are halophytes

• Polyphylogenetic origin

Flowers et al. (2011) Functional plant biology

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Halophytes

Salicornia dolichostachya on the island of Texel, The Netherlands

Glycophytic crops and ornamentals

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Strategies to develop salt-tolerant crops

 Domestication of halophytes • Growth rate, yield, undesirable components

 Classical or marker-assisted breeding of conventional crops • Limited success; probably not enough genetic potential among the cultivars • Variation concerns low-level salt tolerance • Although some success with increased salt tolerance in wheat Munns et al. 2012

 Genetic engineering • Knowledge of salt-tolerance mechanisms and their genetic determinants; at present not available

Strategies to develop salt-tolerant crops

 Domestication of halophytes • Growth rate, yield, undesirable components

 Classical or marker-assisted breeding of conventional crops • Limited success; probably not enough genetic potential among the cultivars • Variation concerns low-level salt tolerance • Although some success with increased salt tolerance in wheat Munns et al. 2012

 Genetic engineering • Knowledge of salt-tolerance mechanisms and their genetic determinants; at present not available

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Domestication Salicornia spp.

Drip-irrigation experiment with Salicornia

Containers with • Salinity irrigation Salicornia on coarse water? sand • Additional nutrients? • Germination? • Yield • Nutritional value Reservoir with pump

Domestication Salicornia spp.

Drip-irrigation experiment with Salicornia www.zeekraalwijzer.nl

• Cultivation • Origin Salicornia in supermarkets • Quality criteria • Nutritional value

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Domestication of halophytes

Salicornia in the supermarket

• Sea beet • Sea kale • Common melilot • Quinoa

Strategies to develop salt-tolerant crops

 Domestication of halophytes • Growth rate, yield, undesirable components

 Classical or marker-assisted breeding of conventional crops • Limited success; probably not enough genetic potential among the cultivars • Variation concerns low-level salt tolerance • Although some success with increased salt tolerance in wheat Munns et al. 2012

 Genetic engineering • Knowledge of salt-tolerance mechanisms and their genetic determinants; at present not available

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Classical or marker-assisted breeding of conventional crops

• Success story: Increased salt tolerance in durum wheat (Munns et al. 2012)

X

Durum wheat Ancestral Bread wheat TmHKT1;5 TmHKT1;5 > Increase of 25% seed yield in durum wheat under saline conditions

Strategies to develop salt-tolerant crops

 Domestication of halophytes • Growth rate, yield, undesirable components

 Classical or marker-assisted breeding of conventional crops • Limited success; probably not enough genetic potential among the cultivars • Variation concerns low-level salt tolerance • Although some success with increased salt tolerance in wheat Munns et al. 2012

 Genetic engineering • Knowledge of salt-tolerance mechanisms and their genetic determinants; at present not available

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Salt-tolerance mechanisms in

halophytes Genes involved in Na+ transport processes

• Salt tolerance is a multigenic trait

• Function of a gene depends on the level and location of expression

Salt-tolerance genes in Salicornia

 Unique growth-stimulation in response to salt

Salicornia dolichostachya

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Growth in response to salinity Spinacia versus Salicornia

Results

 Enhanced SOS1 expression and suppression of HKT1;1 in Salicornia in comparison with Spinacia

+ Na+ Na SOS1 XHKT1;1

Na+ Cl- Cl- - + + Cl Cl- Na Na K+

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Results

 At low external salinity: Leaf cell Constitutive activity of the vacuolar Na+ Cl- H+-pumps and the Na+/H+ exchanger in Salicornia

 At high external salinity: Better Na+ retention inside the vacuole in Salicornia in comparison with Spinacia Na+ Cl- Cl- - + + Cl Cl- Na Na K+

Prospects

 Engineering salt tolerance in glycophytic crops • Indentification of the key processes and genes • Confirmation of these candidate salt tolerance genes • Pyramiding of validated salt tolerance genes in target crop species

Na+  Domestication of halophtes Cl- Cl- - + + Cl Cl- Na Na K+

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 Thank you for your attention

Na+ Cl- Cl- - + + Cl Cl- Na Na K+

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