PtrWRKY75-overexpressing transgenic poplar showed
improved drought tolerance under long-term drought stress
To further explore the function of PtrWRKY75 in long-term drought
stress, the OE lines and WT were subjected to 35 days of soil RWC at
70% (control) or 20% (drought). On day 35, the OE lines showed better
growth than that of WT (Figure 6A). Compared with WT, the OE lines had a
higher leaf RWC, indicative of stronger drought tolerance (Figure 6B).
The OE lines and WT showed no significant differences in photosynthetic
rate in the control (70% soil RWC), but the OE lines had a higher
photosynthetic rate under drought conditions (Figure 6C).
To investigate the difference in growth between OE lines and WT, we
monitored the plant shoot elongation rate and biomass under well-watered
and drought conditions. The shoot elongation rate was significantly
higher in OE lines than in WT under 20% RWC, but not significantly
different between OE lines and WT under well-watered conditions (Figure
6D). After long-term drought treatment, consistent with the
photosynthetic rate, the biomass accumulation was higher in the two OE
lines (by 35.003% and 46.32%, respectively) than in WT under low soil
RWC conditions, but not significantly different between the OE lines and
WT under well-watered conditions (Figure 6E).
The chlorophyll a , chlorophyll b , and total chlorophyll
contents were not significantly different between OE lines and WT under
70% soil RWC, but were significantly higher in the OE lines than in WT
under long-term drought conditions (Figure S3A–C). This result
indicated that the OE plants showed a better ability to absorb light
energy compared with WT, and thus maintained a higher photosynthetic
rate under long-term drought conditions. Compared with WT, the OE lines
also showed higher maximal photosystem II (PSII) quantum yield
(F v/F m) after long-term
drought treatment (Figure S3D).Therefore, overexpression ofPtrWRKY7 5 was beneficial for plant growth under long-term drought
conditions.