Figure 4. Light signaling pathways contributing to drought tolerance.
Drought stress results in biosynthesis of ABA leading to ABA-dependent gene regulation causing drought tolerance. In addition, stomata close preventing water loss via transpiration. Under shade conditions (low R:FR ratio), ABA biosynthesis is stimulated which results in the induction of ABA-induced gene expression causing drought tolerance. Low R:FR ratios also increase the sensitivity to ABA causing increased drought tolerance. Also, phyB acts on stomatal opening in a COP1- or PIF3/PIF4-dependent way to regulate stomatal closure. Blue light perceived by CRY1 and PHOT1/PHOT2 represses the inhibitory function of COP1 on stomatal opening resulting in closed stomata thereby increasing drought tolerance. For more information concerning the different pathways, please refer to section 4. Abbreviations: ABA, abscisic acid; R, red light; FR, far-red light; B, blue light.