Abstract
During development, signaling networks specify stomatal cell fate and patterning in response to phytohormones. A number of studies in the past few years have revealed that brassinosteroids repress the signaling pathway that inactivates SPEECHLESS (SPCH), promoting stomatal cell fate determination in the hypocotyl. These plant hormones also control stomatal patterning specification by regulating genes in the TTG/BHLHs/MYBs/GL2 network. Gibberellins, like brassinosteroids, promote stomatal formation in the embryonic stem, which suggests that their signaling pathways may converge. These phytohormones also regulate LLM-domain B-GATA factors. The involvement of these factors as positive regulators of stomatal formation, which function upstream of SPCH, suggests that the brassinosteroid and gibberellin signaling pathways may converge to control stomatal cell fate specification. In addition, the leucine-rich repeat-containing receptor-like protein TOO MANY MOUTHS acts later than these hormones in the cell division sequence that triggers stomatal formation, and it also appears to control stomatal initiation in response to brassinosteroids. The emerging picture suggests that crosstalk among hormones and signaling networks guides stomatal cell fate determination and patterning in the hypocotyl.
Highlights
The Arabidopsis epidermis has attracted widespread attention as an excellent model system for studying the molecular mechanisms underlying cell fate determination and pattern formation in plants
To form the complex consisting of TESTA GLABRA (TTG), GL3, and/or ENHANCER OF GLABRA3 (EGL3) and CPC or TRY, CPC, whose gene is expressed in files characterized by the absence of stomata [20,22], moves to the stomatal-forming cell files where it competes with WER in basic helix-loop-helix (BHLH) protein binding [20]
Does the TTG-BHLH-MYB-GL2 network interact with the brassinosteroid and/or gibberellin signaling pathway? the cpc mutant shows increased stomatal production in response to brassinolide treatment, the try cpc mutant exhibits absolute insensitivity to this plant growth regulator [5]. These findings strongly suggest that brassinosteroids positively regulate stomatal development upstream of CPC and TRY and that cpc responds to this phytohormone due to genetic redundancy [5]
Summary
The Arabidopsis epidermis has attracted widespread attention as an excellent model system for studying the molecular mechanisms underlying cell fate determination and pattern formation in plants. Factors such as the rapid growth of the hypocotyl, which completes its development within 1 week after germination, as well its simplicity, have encouraged researchers to delve into the development of this embryonic organ. During the past several years, our understanding of the molecular mechanism that guides stomatal cell fate specification and patterning has advanced due to the identification of a number of hormones and genetic networks involved in these processes. It appears to promote the initiation of stomatal development in response to brassinosteroids [5]
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