New technologies in animal and plant breeding Helen Sang University of Edinburgh
“Genome editing”
• DNA is packaged into chromosomes • Humans have 1.8metres of DNA • Each chromosome is a linear array of genes, each of a unique sequence
“Genome editing”
Genome editing involves the use of “molecular scissors” to identify a specified gene sequence and then cut the gene at the target site
“Genome editing”
The DNA at the cut site may be replaced with a very short stretch of new DNA
CRISPR: sequence-specific editing
• • • •
CRISPRs are the most recently developed molecular scissors CRISPRS are very efficient in finding the target sequence and cutting DNA Cut DNA may be repaired but not precisely, causing a novel mutation Cut DNA may be repaired using a different sequence, introducing a precise genetic change
Mutation of a target gene: resistance to PRRS a major viral disease of pigs
University of Missouri and Genus PLC Mutation of a specific gene, required for the infection of pigs by PRRS virus, results in resistance to infection
Gene editing in a Brassica crop: pod shatter in oil seed rape a
b
c
Wild type
Edited
d
Wild type
Edited
A single mutation in a model brassica species stops pod shatter Introduction of a similar mutation in oil seed rape should greatly Lawrenson et al. Genome Biology 2015 reduce losses of seed
Replicate a natural mutation in different breeds
Recombinetics
Beef cattle are hornless, the polled mutation; the majority of dairy cattle have horns that are removed in calves. Gene editing has been used to make dairy cattle hornless.
Move genetic variation between species: African Swine Fever virus
Bruce Whitelaw and colleagues, The Roslin Institute
Aquaculture: main source of fish protein globally, Require source of omega3 fatty acids in diet
Wild fish mainly take up omega3 LC-PUFAs via the food chain
Primary producers of omega-3 LCPUFAs are algae
Farmed fish has to be fed with omega-3 LCPUFAs
Need a sustainable source of omega-3 LCPUFAs
Reduction fisheries are limiting growth of aquaculture
Can an oil seed crop be genetically altered to form a source of omega3 fatty acids for farmed fish food? http://www.rothamsted.ac .uk/camelina-2015
Nitrogen availability limits crop yields
Legumes are the prototype for self-fertilising crops Aim: genetically alter cereals to fix nitrogen, adopting the mechanisms used by legumes e.g.peas https://www.jic.ac.uk/
New breeding technologies using molecular techniques • Simple gene mutation: equivalent mutations could exist “naturally”; much faster than breeding • Move gene variant between breeds: avoid loss of genetic merit; much faster than breeding • Move gene variants between species; cannot be achieved by breeding • Introduce novel genes not present in particular species e.g. blight resistance; may involve introduction of new DNA sequences • Introduce novel genetic pathways to enhance qualities; complex combination of very small genetic changes and inroduction of new gene sequences Parallel increase in knowledge of genome sequences/gene structure/gene function in crops and farmed animals (and their diseases) results in opportunities to use GE to increase productivity faster
