Table 1. Some important groups of eukaryotic histidine kinases (HKs), their known input signals, and their output responses.

HK group	Structure	Presence in eukaryotes	Input signal	Output response	References
Ethylene receptors		Plants, Algae, Fungi, Amoebae,	Ethylene	Plants: seed germination, leaf senescence, fruit ripening, defenses to pathogens	Ju et al., 2015 60 Hérivaux et al., 2017 61 Kabbara et al., 2019 64
CHASE-HK		Plants, Algae, Fungi, Amoebae,	Cytokinins	Plants: cell division, embryogenesis, vascular tissue development	Kaltenegger et al., 2018 74 Hérivaux et al., 2017 61
AHK1/Fungal group VI		Plants, Algae, Fungi	Osmostress Oxidant stress	Plants: seed desiccation, vegetative stress tolerances Fungi: osmotic and oxidant adaptation	Defosse et al., 2015 53 Nongpiur et al., 2019 87
Phytochromes		Plants, Algae, Fungi Amoebae,	Red/far red light	Plants: phototropism Fungi: vegetative growth, sexual reproduction	Rensing et al., 2016 88 Yu and Fischer, 2019 89
CKI1		Plants	Cytokinins?	Development of female gametophyte	Yuan et al., 2016 92 Liu et al., 2017 93 Yuan et al., 2018 94
CKI2/AHK5		Plants	?	Stress-induced stomatal closure, salt sensitivity, and resistance against microbial infection	Pham et al., 2012 95 Mira-Rodado et al., 2012 96 Bauer et al., 2013 97
Fungal group III		Fungi, Amoebae	Osmostress	Fungi: oxidant adaptation, development, virulence	Defosse et al., 2015 53 Hérivaux et al., 2016 54 Kabbara et al., 2019
Fungal group X		Fungi, Algae, Amoebae	Oxidant stress ?	Fungi: oxidant adaptation, development, virulence	Defosse et al., 2015 53 Hérivaux et al., 2016 54 Kabbara et al., 2019 64

KEY

:Dimerization histidine phosphotransfer domain     :Catalytic ATP-binding domain     :Rec eiver domain     : cGMP-specific phosphodiesterases- Adenylyl cyclases- FhlA domain     :Ethylene Binding Domain     :Cyclases/ Histidine kinases Associated Sensing Extracellular     :Trans membrane Region     :Calcium channels and Chemotaxis receptors domain     :Period circadian protein- Aryl hydrocarbon receptor nuclear translocator protein- Single-minded protein     :Phytochrome domain     :Histidine kinases- Adenylate cyclases- Methyl accepting proteins and Phosphatases     :Serine/ Threonine kinase related domain