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. 2022 Jul 26;14(4):779–803. doi: 10.1007/s12551-022-00985-z

Fig. 5.

Fig. 5

Photoregulation of stomatal development which determines protodermal cell divisions and resulting stomatal index and stomatal density at epidermis by ultraviolet A (UV-A) and B (UV-B), blue (B), green (G), red (R), and far red (FR) light. a Light spectral ranges and the groups of photoreceptors that participate in the regulation of stomatal pattern. UV-B light acts via UVR8 photoreceptor and via nonspecific absorption by various cell components, regulating stomatal development in an opposite manner. Blue light via phots and crys, red light via phyB and far red light via phyA increase stomatal index. Photosynthetic apparatus (PSA) in underlying mesophyll regulates stomatal index and stomatal density via photosynthetic products and/or carbon dioxide concentration changes. b Key components of the most well-studied signalling pathways involved in photoregulation of stomatal development. Photoreceptors phyA, phyB and crys (cry1/2) act in concert to promote light-induced stomatal development via COP1 (E3-ubiquitin ligase), YDA (MAPK kinase kinase, heading MAPK kinase cascade) and transcription factors (SPCH, MUTE and FAMA — closely related bHLH transcription factors, which regulate consecutive steps in the differentiation pathway of stomata), critical for the development of stomata from the protodermal cell. YDA might be positively regulated by COP1 through yet unknown mechanisms (dashed arrow) and inhibits downstream transcription factors probably via their targeting by phosphorylation. PIF4 transcription factor represses SPCH expression, and phyB, inhibiting PIF4, derepresses SPCH, increasing stomatal development. Besides, light promotes ANGUSTIFOLIA3 (AN3) at transcriptional and post-translational levels, likely through the photoreceptor-mediated pathways (crys and probably phys as well), which then downregulates the expression of COP1 and YDA (Wei et al. 2020). Light-green rectangular matches promoting, and pink rectangular matches restricting conditions for photosynthesis. Double line matches regulation on transcription level