Two-component systems

Role in plants

Plants contain proteins with sequence similarity to histidine kinases, response regulators, and phospho-relay proteins. At first glance, this seems to indicate that two-component signaling systems are functioning much the same way in plants as in bacteria. However, some of the proteins with similarity to histidine kinases lack amino acid residues considered essential for histidine kinase activity. Following are some of the pathways which involve proteins related to histidine kinases.

(1) Ethylene. A family of at least 5 proteins appear to function as ethylene receptors in Arabidopsis. All five contain a histidine kinase-like domain. In two of these proteins (ETR1 and ERS1) there is complete conservation of the residues considered essential for histidine kinase activity. Several of the ethylene receptors are hybrid kinases, containing a response regulator-like domain in addition to the histidine kinase-like domain.

(2) Cytokinin. Overexpression of the CKI1 protein in Arabidopsis results in cytokinin-independent growth. CKI1 contains a histidine kinase domain with the all the essential residues essential for activity. CKI1 is a hybrid kinase.

(3) Red light/Phytochrome. Plant phytochromes contain histidine kinase-like domains, but in all cases there is substantial divergence from the canonical requirements for activity. Interestingly, in cyanobacteria, there is a functional phytochrome histidine kinase and cognate response regulator.

(4) Pyruvate dehydrogenase. The pyruvate dehydrogenase of animal mitochondria has the features of a histidine kinase but appears to function as a serine kinase. Plant mitochondria and plastids contain a similar proteins.

Arabidopsis genes