Target Traits

HideShow resource information
View mindmap
  • Target Traits for Crop Improvement
    • Disease Resistance
      • Durable disease resistance
        • gene-for-gene resistance is not durable
          • almost never complete immunity
          • R genes lose effectiveness
            • Wheat varieties: Torch, Stigg, Warrior
            • Mildew resistance breakdown in Barley: Pipkin Mla13
            • yellow rust in wheat: Sleipnar Yr9
          • more useful in veg
          • Pathogen surveys
          • R genes select for Avr mutation
      • Breeding for DR in wheat
        • Example: Eyespot
          • Fungi blocks stem, causing it to break
          • Assessment of Resistance
            • Seedlings: scoring system based on leaf sheath penetration
            • Adults: score % stem circumference diseased
          • Resistance genes in wheat
            • Pch2 found on chromosome 7AL
              • Only useful in early stages
              • Doesn't protect against all eyespot varieties
            • Pch1 on chromosome 4VL in D. villosium
              • only resistant to O. yallundae
              • To introgress from wild species: cross w/ T. persicum to produce fertile amphidiploid; then cross w/ common wheat (eg Marne) => VPM-1
              • Large introgression retained
                • Difficult to map region
                • Presence charcterised by endopeptidase isozyme profiles
              • Associated with: higher protein content; lower yield
            • Pch3 5AL found in Copelle variety
              • QTL Mapping
        • Problems for breeding in wheat
          • Lack of co-dominant markers
            • wheat SSR markers do not amplify from Ae. ventricosa
            • Errors from null amplification
            • Not possible to identify heterozygotes in segregating F2 populations
            • SNPs may not function in wild relatives
            • Can use Brachipodium distachyon to develop co-dominant markers
              • Smaller genome
              • Syntenic with wheat
          • Fine Mapping the Region
            • In wheat: little recombination, potent effect, single gene
            • In Ae. ventricosa: free recombination, potent effect
      • GM resistance
        • Gaeumannomyces graminis var. tritici
          • Avenacin A-1 production by oats: antimicrobial
            • Put the Avenacin biosynthesis pathway into wheat using golden gate
        • Transgenic approaches for PTI
          • AtEFR in wheat can respond to elf18 and then trigger defence gene expression and later callose deposition
            • EFR confers resistance to multiple pathogens: a feature of PTI
            • Able to give resistance to tomato, N. benthamiana and wheat
          • Score resistance with incoulation, Measure lesion size & bacteria number
            • Create chimeric genes to increase PTI potency
        • Gene-based markers for PRRs/PTI
          • Quantitative disease resistance
            • MAPK phosphorylation
            • ROS
            • Callose depositation
            • Seedling growth inhibition
            • PAMP Induced Resistance
            • Defense gene expression
          • GWAS: identify DNA markers for breeding that associate with resistance
      • NB-LRRs
        • NB = Signalling; LRR = Receptor
      • MutRenSeq
        • Create mutants of wildtype resistant wheat; look for SNPs in the mutants which lose resistance
        • Massively sped up the process of introducing a gene
          • Can create a cloned gene library to transform a stack of resistance genes
    • Abiotic Tolerance
      • Water
        • Physiological responses
          • Avoidance: Bigger root systems; Prevention of water loss; earlier flowering
          • Acclimation : Stress forces plant to select for new traits, waxy leaves, decreased stomatal conductance
          • Tolerance: No new traits but processes are effected. Eg, osmotic adjustment, increased cell wall extensibility, increased antioxidants and increased protein repair and turn over
        • Examples
          • Marker assisted selection: increased deeper rooting in rice
          • Decreased anthesis-silking interval in maize
          • droughted yield QTLs in pearl millet
          • INcreased water use efficiency in wheat
          • cspB will protect against growth of plants during stress
          • ARGOS inhibits ethylene, which prevents groth by DELLA (CRISPR)
        • Selection methods
          • Empirical selection: select for tolerence in dry conditions, can mean low heritability, very slow
          • Indirect selection via secondary traits
          • Marker assisted selection
      • Phospherous
        • Factors influencing P nutrition
          • Genetic
            • Uptake systems
              • Pht genes regulate the transport of Pi by transcribing P-starvation genes
            • Rhizosphere
            • Root architecture
            • Symbioses
              • Mycorrhizal fungi: mtpt4 gene
            • Assimilation
          • Environment
            • Availability
            • Micro-organisms
            • Soil type
            • Season and latitude
            • Growth rate
            • Other nutrients
            • Photo-synthesis
      • Nitrogen
        • Root Architecture
          • ANR1 transcribed in response to NO3, causes root elongation
        • Nitrate transporters
          • NRT2 family = high affinity at low NO3 concentration
            • Post translation modification switches NRT1.1 between high and low affinity
        • Root Nodule Symbiosis
          • Can we engineer N2 fixing in crops?
            • Would include introduction of >50 genes
            • 3 Steps to engineer highly efficient rhizobia symbiosis
              • Symbiosis signalling pathway
              • Nodule Formation
              • Bacterial infection process
      • Sulphur
        • Driven by proton cotrancport
          • SULTR1;1 and 1;2 = high affinity soil->root
          • SULTR 2 and 3 = transfer sulphate in xylem parenchyme
          • SULTR 4;1 and 4;2 = transport stored sulphate from vacuole
        • transport TFs = MYB
        • Transport inhibitor = SLIM1
        • ETHE1 mutants => fatal toxicity
      • Metals
        • Narrow optimum concentration
        • Highly pH dependent
        • Fe Uptake
          • Reduction: pump protons into soil
          • Chelation
          • Up-regulated in deficiency
        • Applications
          • Over-expression to gain more minerals
          • Hyper-accumulators to remove toxins
        • Transport
          • Chelators and chaperones bind
          • Testing: yeast; oocyte injected with RNA to be tested
    • Nutritional Quality
      • Seed oils
        • Undesirable contents to be removed, desirable to be increased
      • Soy bean oil
        • FAD2 and 3 genes => high oleic acid, low linolenic acid
      • Wheat starch content
        • switch fibre to starch ratio
        • grains are mostly starch
        • Resistant starches are healthier
        • Yield, quality penalties?
    • Flowering time
      • Eg. Brassicas
        • 'weedy' canopy structure
          • indeterminate, late formed flowers and branches high in the canopy
        • structure means reduced light
          • Reduced light and lack of erectness cause later flowering
        • productivity decreased by late flowering
    • Plant Growth
      • Prevention of lodging in cereals
        • Rht1 dwarfing gene in wheat
        • Sd1 in rice
        • causes GA insensitivity => reduced cell elongation
      • Different yield factors
        • Amount of sellable yield
          • eg. Wheat: no tillers, no grains, grain weight
        • Increase yield v protecting yield
        • eg. Wheat
          • GW-A = grain width; GL-A = grain length
          • Polyploidy leads to redundancy and can create 'breaks' in potential yield increase
            • eg. wheat TaGW2-A breke, knock out increases TGW by 5%

Comments

No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Genetics resources »