Signaling molecules and transcriptional reprogramming for stomata operation under salt stress

Abiotic stresses such as salinity and other unfavorable conditions affect more than half of the crop production in the world. Salinity ranks as the second limiting factor after drought. By 2050, over 50% of the world arable land will most likely be affected by salinity. Salinity stress reduces water availability and affects stomatal movement in plants. Under salt stress, guard cells are reprogrammed at the transcriptional level to conserve water by more efficient stomatal operation. The intertwined signaling network consisting of signal molecules (such as ABA, JA, Ca^{2 +}, NO, H₂S, ROS) and various transcription factors (such as MYB, NAC, bZIP, WRKY family members) fine-tune the stomatal aperture, optimizing leaf gas exchange. Many of these transcription factors are essential for activating the basic components of signaling pathways, from stress receptors to protein kinases and membrane effectors, mediating stomata movements. Among these signaling molecules, abscisic acid (ABA) is considered as the core member. Most of the other molecules are ABA-dependent or work as secondary messengers to increase ABA production. Active molecules such as reactive oxygen/nitrogen species are thought to cause oxidative stress in plants, but in controlled quantity can also act as signals in plant defense mechanisms. This review focuses on the signal molecules and transcription factors involved in regulating stomatal opening to optimize the performance of plants under saline conditions.