The HIC signalling pathway links CO2 perception to stomatal development

Stomatal pores on the leaf surface control both the uptake of CO2 for photo synthesis and the loss of water during transpiration. Since the industrial revolution, decreases in stomatal numbers in parallel with increases in atm ospheric CO2 concentration have provided evidence of plant responses to cha nges in CO2 levels caused by human activity(1,2). This inverse correlation between stomatal density and CO2 concentration also holds for fossil materi al from the past 400 million years(3) and has provided dues to the causes o f global extinction events(4). Here we report the identification of the Ara bidopsis gene HIC (for high carbon dioxide), which encodes a negative regul ator of stomatal development that responds to CO2 concentration. This gene encodes a putative 3-keto acyl coenzyme A synthase-an enzyme involved in th e synthesis of very-long-chain fatty acids(5). Mutant hic plants exhibit up to a 42% increase in stomatal density in response to a doubling of CO2. Ou r results identify a gene involved in the signal transduction pathway respo nsible for controlling stomatal numbers at elevated CO2.