The invention provides a synthetic phytase polynucleotide which is optimized for expression in plants and which encodes at thermotolerant phytase, as well as isolated thermotolerant phytase enzyme. Also provided are feed or food products comprising a thermotolerant phytase, and transgenic plants which express the thermotolerant phytase. Further provided are methods for making and using thermotolerant phytases, e.g., a method of using a thermotolerant phytase in feed and food processing.