Rice

Question 1

Key facts about rice

Answer 1

• Rice feeds ~ ½ people on earth (major calorie provider for 3.5bn people)
• Highest production in S. E Asia and China (no exports in china who stock pile)
• 90% rice consumed by those who grow it
• Restricted growth regions: Requires high temps, water and sensitive to day lengths
• Grain = mostly starch 94%, v little protein / lipid + is v nutrient poor ( as vitamin A is in leaves and brown bran layer which is removed due to its toxicity)
• V labour intensive to grow – 92 days per hectare x 3 rice season per year = 276 days + need family / friends to help (hard to break out of poverty as takes long time and no money left for education / health)

Question 2

We need a yeild increase

Answer 2

• Yield has already increased (from 1 to nearly 4 tonnes per hectare now)
• by a further 50% yield increase needed by 2050 in developing world
• Requirement to imporve yeild, nutrition and reduce fertiliser use

Question 3

Rice phylogeny

Answer 3

Ancestor = Orzya rufipogon
Main modern cultivated = O. sativa (Asian)
sub variety = O. indica (non-stick long grain)
sub variety = O. japonica (sticky short grain)

> 120,000 different named cultivars

Origin:
- highly debated (inbedded in tradition)
- 400 ancestor genomes and 1000 domesticated rice genomes were sequenced to build tree and found 2 independent origins.
- SE Asia and China

Question 4

Early Rice domestication

Answer 4

QTL analyses used to associate regions of DNA with the phenotypic traits (involves back crossing)

Perennial -> Annual

Prostrate -> upright
- Chr7 – Prostrate growth 1 (PROG1) gene
- Single base mutation T-A changes aa. causing plant to grow upright instead of along ground
- PROG-1 Encodes zinc finger protein (like tb1) which is expressed in axillary meristems (like tb1) and promotes prostrate growth and tiller outgrowth
- Mutant leads to upright growth with no branches.

Many tillers -> few tillers
- Chr7 – Prostrate growth 1 (PROG1) gene

shattering seeds -> no shaterring
- SH4 gene
- SH4 plays a role early in AZ differentiation by postiviely regulating the expression of SHAT1 which specifies abscission zone developement

red seeds -> white seeds
- Chr7 Rc gene
- Rc encodes bHLH transcription factor leading to production of proanthocyanidin leading to red colour of seed
- 14bp deletion in japonica -> lose DNA binding domain of TF -> loss of function -> white colour

• poor yeild -> good yeilds

3 major mutations

Question 5

Rice domestication in the last 20 years: Flood resistance

Answer 5

The problem with rice and water
- Rice dies w/in 7 days of submergence of heads under water -> total yield loss
- Floods = v frequent (more common w/ climate change)

Sensitive varieties: panic in floods and grow v fast so leaves above water + can breathe -> water retreats (as floods often temporary / transient) and plant stem can’t support itself so collapses + dies
-> e.g. Swarna (low tolerance but high yeild)

Sub1 varieties: flood resistant rice goes dormant when submerged
-> e.g. Sub (high tolerance but low yeild)

Solution -> cross plants
- takes several generations to remove genetic content surrounding the sub1 gene

Question 6

Rice domestication in the last 20 years: Golden rice etc

Answer 6

**Golden rice **
Rice is a nutritionally poor grain
-> lacks 2 enzymes (phytoene synthase and Carotene desaturase ) to make β-carotene (vitamin A precursor)

Solution:
-> Get enzymes from other plants to express gene to make vitamin A rich rice
-> V1: daffodil and soil bacterium (3kg required)
-> V2: maize and soil bacterium (150g required)

Potential impact:
-250million children <5 suffer vitamin A deficiency (1% / 2.5 million die each yr, 10 million go blind)

Problem
- GM rice blocked by NGOs -> Green pieace has been destroying field sites for last 20 years
- Trials finally passed in philopenes in 2021 but GP managed to persuade the supreme court to block the use

Other GM rice that has been blocked:
- Bt rice - makes rice resistant to lepidopteran pests and was ready to release in 2009 -> few lepidopteran pests to protect against so not worth it
- Ht rice – makes rice resistant to roundup so fields can be sprayed -> paddy fields great weed control so may not be worth it

Future aims
- rice blast resistance
- Improved nutitional quality and yeild
- reduced input/ higher resource use efficiency

Question 7

Rice domestication in the next 20 year

Answer 7

Requirments
- increase herbicide tolerance, insect resistance and rice blast resistance (has been done by GMO that are not released)
- Increase yeild by 50%
- Imporve Nutritionan quality – Vitamin B1, Iron, protein, Vitamin A
- Reduced inputs – improve nitrogen fixation (reduce fertilizer), improve drought tolerance (reduce water).

Potential solution: C4rice
- Modify rice to become C4 rather than C3 plant -> C4 adapted to hot and dry environments with good water use efficiency
- increase yeild, reduce fertiliser requirment and increase drought toelrance
- Expand where rice can grow -> Dessert?

Question 8

Overview

Answer 8

Rice is vital world wide

3 stages of evolution
- early domestication
- late domestication -> drought tolerance and golden rice
- Future domestication- C3- C4?