# Overexpression of _PtDXS_ Enhances Stress Resistance in Poplars
## 2 Results
### ABA, GA3, and GA4 Contents of PtDXS-Overexpressing Plants  
HPLC-MS/MS was used to quantify the ABA, GA3, and GA4 contents of the transgenic and WT plants (Figure 6A,D). The ABA content of the transgenic plants (2 \(\pm\) 0.2 ng/g) was approximately 1.6-2-fold that of the control plants. In addition, there was a significant difference in ABA content between the transgenic and WT plants. The GA3 content of the transgenic plants was approximately 4-14-fold that of the control plants. The highest GA3 content was in the T3 plants (1.51 ng/g). The GA4 content of the T1 plants was 0.65 \(\pm\) 0.05 ng/g. By contrast, GA4 was not detected in the T3 and WT plants.  
Resistance to Septotis Populiperda Infection of PtDXS-Overexpressing Plants and Feeding of Micromelalpha troglodyta on WT and PtDXS-Overexpressing Plants  
Most terpenoids have bacteriostatic and bactericidal effects and can enhance plant disease resistance. In addition, terpenoids can resist natural enemies. For example, terpenoids as food inhibitors and toxic substances have a direct effect on insect feeding, as well as a toxic influence on insects during feeding [31]. _Septotis populiperda_ causes large-spot disease of poplar. Conidia appeared in WT plants 2 days after inoculation, compared to 4 days in the transgenic plants (Figure 7A). Moreover, the spread of pathogens was greater in the WT than in the transgenic plants (Figure 7B). _Micromelalpha troglodyta_ larvae nibble on poplar leaves, which markedly reduces the quality of poplar. Feeding of _Micromelalpha troglodyta_ was reduced on the leaves of the transgenic plants (Figure 8A,C). In addition, _Micromelalpha troglodyta_ preferred leaves of the WT to those of the transgenic plants (Figure 8A,C). Finally, feeding by _Micromelalpha troglodyta_ on WT poplar leaves was greater than that on transgenic plants (Figure 8D).  
Figure 5: Expression levels of MEP- MVA-, ABA-, IAA-, and GA-related and downstream genes in the transgenic and WT poplar leaves. (**A**) Expression levels of _DXR_, _MCT_, _CMK_, _HDS_, and _HDR_. (**B**) Expression levels of _ACL_, _HMGS_, _HMGR_, _MVK_, and _MVD_. (**C**) Transcript levels of _IDI_, _GPS_, _GPPS_, and _GGPS_. (**D**) Expression levels of _NCD1_, _NCD3_, _NCD5_, _NCD6_, _ZEP1_, _ZEP2_, and _ZEP3_. (**E**) Expression levels of _IAA1_, _IAA2_, _IAA6_, _IAA18_, and _IAA19_. (**F**) Expression levels of _GA20 OX-1_, _GA20 OX-2_, _GA20 OX-3_, and _GA20 OX-4_. All experiments have been normalized using _\(\beta\)-actin_ as an internal reference; bars represent means \(\pm\) SD (\(n=3\)). Three independent experiments were performed. The asterisks represent significant differences relative to WT plants (Student’s \(t\)-test; *, **, and ***, \(p<0.05\), \(p<0.01\), and \(p<0.001\), respectively).  
Figure 6: ABA, GA3, and GA4 contents in the transgenic and WT plants by HPLC-MS/MS. (**A**) Raw data and ABA, GA3, and GA4 contents of WT plants. (**B**) Raw data and ABA, GA3, and GA4 contents of T1 plants. (**C**) Raw data and ABA, GA3, and GA4 contents of T3 plants. (**D**) Comparison of the ABA, GA3, and GA4 contents of transgenic and WT plants. Asterisks represent significant differences relative to WT poplars (Student’s \(t\)-test; **, and **, \(p<0.01\), and \(p<0.001\), respectively).