<p dir="ltr">The hairy root transformation system is a promising tool for genetic engineering for functional characterisation in Eucalyptus nitens, a cold-tolerant eucalypt. This study used the hairy root system to overexpress the defense gene, <i>AtNPR1</i>, in <i>E. nitens in vivo</i>. An endogenous increase in <i>PR-1</i> expression in response to <i>AtNPR1</i> overexpression was found. </p>