Improving Submergence + Waterlogging Tolerance Flashcards
Natural strategies to improve submergence
Happen @ different developmental stages
-> germination
-> stems
-> leaves
Anaerobic germination
- Wheat
- Barley
- Maize
- Oat
- Rice
- E. crus-galli (rice weed)
Anaerobic germination mechanism
- rapid coleoptile extension + emergence; “snorkel”
- oxygen stimulus permits shoot and root emittance
Normal condition for germination
- embryo induces alpha-amylases in aleurone layer via GAs
- high sugar levels inhibit amylase expression
- manages starch consumption (speed, availability)
Anoxia condition for germination
- rice: GA-independent α-amylase induction
- different α-amylase used
Submergence-induced heterophylly
- alternative leaf morphology
- no epidermal stomata: Raninculus trichophyllus
- inhibited leaflet expansion: Potamogetol perfoliatus
- Callitriche protrusions
What causes heterophylly?
- light quality: Rorippa aquatica
- temperature: Hygrophila afformis
- humidity
- all of these are controlled by hormones
Leaf gas films
- an hydrophobic surface generates a GES around/above the leaf
- adaptive to non-continuous flooding
- ^ underwater photosynthesis
- volume around lead where photosynthesis & respiration can still occur
What makes a leaf impermeable?
- study different accessions for hydrophobicity
- Kinmaze: maintains LGFs one day post-submergence
- drp7: does not
- different wax cuticle compositions
Hypoxia avoidance
- rapid elongation for emersion
- deep water rice: rapid internode elongation on submergence
- several ms
- limited exploitability in agriculture
- consumes reserves (< yield)
- induces lodging
aerenchyma
- “snorkel”
- root and shoot tissues can develop hollow cavities to enhance gas transfer from aerial -> submerged tissues
Barriers to ROL
- progressive oxygen impermeabilisation accompanies aerenchyma formation
- enhances SAM delivery
ROL
radial oxygen loss
Without Suberin
- cell wall is porous (3.5-5.2nm)
- H2O, salts, gases interchange
Suberin lamellae
- highly hydrophobic (oxygen impermeable)
- lignin-like aromatic elements connect suberins to lignin
- accumulate under submergence
Adventitious roots
- from the stem
- sustain aeration, nutrient acquisition, growth
Sub1 locus
- 0.06cM
- 120kb
- 8 genes
- submergence tolerance
Sub1 trait segregation
- rice = diploid
- Oryza sativa indica FR13A: flood tolerant (3x ERFVIIs: Sub1a, Sub1b, Sub1c)
- cross with O. sativa japonica M-202: flood-intolerant donor
- F1 = flood tolerant
- self pollination
- F2 = (in)tolerant ; even distribution of molecular markers across different chromosomes
Sub
Submergence-induced
Sub1a
- FR13A: yes
- Nipponbare (intolerant): no
- to prove: KI, KO
How does Sub1a induce tolerance
- Sub1a donor (IR4D931-26): restricted growth
- O. sativa japonica Liaogeng (intolerant) + constitutive expression = sufficient
Restricted growth =
Decreased submergence elongation
Sub1a induces DELLA
Energy-saving, quiescence
Submergence pathway
Sub1a activates SLR1/SLR2 (DELLA), blocks GA (shoot elongation, CHO consumption)
GWAS
- identifying useful genetic loci
- barley accession germination times after short term submergence differs
- > 200 accessions associated with specific SNP round Laccase gene
Laccase
Lignin polymerisation
Is the LAC gene responsible for less germination post-submergence?
- not in exonic regions
- differential expression @ developmental stage 4 in tolerant and sensitive
- deletions in promoter region
Expressing LAC
- ^ seed coat lignification (stain w lignin bind)
- < O2 diffusion -> embryo
- < germination capacity, no seed scarification
Manipulate O2 sensitivity to ^ hypoxia tolerance in crops?
- e.g. Arabidopsis PCO4
- enzyme engineering / gene editing
- variant testing in vitro/ in vivo
- crop translation
Enzyme engineering approaches
1) structure-guided varietal design
2) random mutagenesis
3) directed evolution
Anaerobic germination in cereals?
- rewire existing α-amylases for hypoxia induction
- barley, wheat
Rice anaerobic germination?
- GAMYB TFs increase sugar to meet demand
- can we subjugate to O2 sensing pathway as a chimera?
