Solace does not support mainframe applications directly but Solace can be easily integrated with IBM DataPower appliances which can interface with mainframe applications. The DataPower appliance can handle the transformation requirement of the service and the Solace appliance can handle the messaging portion to provide quick and efficient message delivery downstream.
The 'Solace Integration with IBM Datapower' integration guide, available on the Solace Developer Portal, has more information on this:
http://dev.solacesystems.com/integration-guides/ibm-datapower/
You may also be able to use Solace's REST interface, depending on your Mainframe application. Solace's REST interface allows communication using standard POST HTTP requests.
There are also guides for Solace's REST interface available on the Solace Developer Portal:
http://dev.solacesystems.com/docs/open-apis-protocols-docs/