Water shortage reducesPHYTOCHROME INTERACTING FACTOR 4, 5and3expression and shade avoidance in Arabidopsis

Abstract

In agricultural crops, forests and grasslands, water deficit often occurs in the presence of cues from neighbouring vegetation. However, most studies have addressed separately the mechanisms of plant growth responses to these two aspects of the environment. Here we show that transferringArabidopsis thalianaseedlings to agar containing polyethylene glycol (PEG) to restrict water availability reduces hypocotyl growth responses to shade without simultaneous affecting cotyledon expansion or its response to shade. Water restriction diminished the activity of thePHYTOCHROME INTERACTING FACTOR 4 (PIF4), PIF5, PIF3andPIF3-LIKE 1gene promoters, particularly in seedlings exposed to simulated shade. The response ofPIF4expression to PEG required the presence of its positive morning regulators CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY), which also reduced their expression in response to PEG. Water restriction diminished the nuclear abundance of PIF4 in hypocotyl cells only in the seedlings exposed to shade. In addition to the changes inPIF4levels, post-transcriptional processes also contributed to the response to PEG. Hypocotyl growth showed significant triple interaction among water availability, shade and the presence of PIF4, PIF5 and PIF3. Collectively, these results unveil PIFs as a hub that interlinks shade and drought information to control growth.

Warm temperature and mild water stress cooperatively promote root elongation

“…This effect tended to decrease somewhat in drier soils albeit not to a statistically significant degree (Figure 1B). This effect is reminiscent of the recently reported inhibition of shade-induced hypocotyl elongation under drought 5 . We compared the root and hypocotyl lengths of each plant in our assay and found a weak negative correlation at 28°C, but not at 20°C (Figure S1A-B).…”

Environmental Control of Hypocotyl Elongation

“…In etiolated seedlings, hypocotyl elongation decreases by half on PEG when the osmotic potential is reduced from -0,1MPa to -0,5MPa 164 . Similar and more negative water potentials also suppress elongation in light grown-photoautotrophic seedlings without affecting cotyledon expansion, and this effect is particularly strong in canopy shade 163 .…”

“…Plant growth critically depends on water availability and signaling networks regulate elongation before water shortage puts cell integrity at risk 162,163 . This conservative growth strategy is presumably favorable for long-term survival.…”

Molecular mechanisms underlying coordinated responses of plants to shade and environmental stresses

“…Consistent with this observation, rice phyB mutant seedlings had reduced total leaf area, stomatal density, and transpiration rate, thereby displaying reduced water loss and improved drought tolerance (Liu et al., 2012). Moreover, polyethylene glycol (PEG)‐induced drought stress strongly decreased the activities of PIF3, PIF4, and PIF5 and inhibited hypocotyl growth in shade, indicating that drought stress signaling impairs the shade avoidance response (Semmoloni et al., 2022). However, the water deficit caused by PEG had no effects on cotyledon expansion in response to shade (Semmoloni et al., 2022).…”

“…Moreover, polyethylene glycol (PEG)‐induced drought stress strongly decreased the activities of PIF3, PIF4, and PIF5 and inhibited hypocotyl growth in shade, indicating that drought stress signaling impairs the shade avoidance response (Semmoloni et al., 2022). However, the water deficit caused by PEG had no effects on cotyledon expansion in response to shade (Semmoloni et al., 2022).…”