Receptor/histidine kinase fusion constructs and uses thereof

A transgenic plant comprising:

• a) a first DNA construct comprising a first plant operable promoter operably linked to a nucleic acid segment encoding a sensor protein, said protein comprising a secretory sequence for directing the protein to the extracellular space of a plant cell and a binding region specific for a target substance of interest, wherein said protein undergoes a conformational change when the target substance is bound;
• b) a second DNA construct comprising a second plant operable promoter operably linked to a nucleic acid segment encoding a protein that comprises the following domains:
• a plasma membrane targeting signal sequence, an extracellular domain for binding the sensor protein, a transmembrane domain and a histidine kinase domain for phosphorylating a protein with nuclear shuttling or transcriptional activating functions, wherein the histidine kinase is activated when the sensor protein binds to the extracellular domain;
• and
• c) a third DNA construct comprising a third plant operable promoter operably linked to a nucleic acid segment encoding a detectable marker or a response gene, wherein the third plant operative promoter is responsive to the transcriptional activator protein, and wherein the detectable marker is expressed when the external target substance of interest is bound to the sensor protein.