Editing plant DNA using a mechanism evolved in bacteria
Last updated: 11 Jun, 2015
Researchers at the University of Georgia have used a gene editing tool known as CRISPR/Cas to modify the genome of a tree species for the first time. By mutating specific genes in Populus the researchers reduced the concentrations of lignin and condensed tannin.
CRISPR technology is derived from a defense mechanism evolved by bacteria and other single-celled organisms. When a bacterium is attacked by an invader like a virus, it captures some of the virus's DNA, chops it up into pieces and incorporates a segment of the viral DNA into its own genome. As the bacterium experiences more threats, it accumulates a bank of past infections in a special part of its gen alic code called CRISPRs--short for clustered regularly interspaced short palindromic repeats--which act as a kind of immune system to protect against future invasions.
Poplar plants produced from a lignin-gene-targeting experiment in C.J. Tsai's lab at the University of Georgia had red-colored wood. Red stem is a known side effect of lignin modification. Image from the University of Georgia (Press release).
In the Letter by Zhou et al., the authors note that for woody perennials with long generation cycles, accelerated breeding is finally within reach using CRISPR genome editing. In addition to this because CRISPR editing at the target loci is biallelic and the transgene (Cas9 and selectable marker) integration is hemizygous, they envision a scenario where CRISPR editing is performed in both male and female clones, such as the early-flowering FT transgenics (Hoenicka et al., 2014). Controlled crosses between male and female primary transformants with confirmed biallelic mutations should in theory produce transgene-free, biallelic mutants in 25% of the progeny (or 6.25% for two-locus crosses). Elite clones carrying targeted gene mutation(s) without foreign DNA may ultimately help increase public acceptance of bioengineered agricultural products.
Read the full letter by Zhou et al., on Early view "Exploiting SNPs for biallelic CRISPR mutations in the outcrossing woody perennial Populus reveals 4-coumarate:CoA ligase specificity and redundancy"