The javax.management.DescriptorKey javadoc as of b55 says:

[...]
An annotation such as @Units can be applied to:

    * a Standard MBean or MXBean interface;
    * a method in such an interface;
    * a parameter of a method in a Standard MBean or MXBean interface when that method is an operation (not a getter or setter for an attribute);
    * a public constructor in the class that implements a Standard MBean or MXBean;
    * a parameter in such a constructor. 

Other uses of the annotation are ignored.
[...]

Let's consider an MBean interface defined such way:

public interface WhateverMBean extends FatherInterface {
}

@MyDescriptorKey(blabla...)
public interface FatherInterface {
	// Here in @MyDescriptorKey is used everywhere is possible.
}

The Descriptor of my WhateverMBean instance does not contain what comes with MyDescriptorKey defined on the super interface.
However, the management interface of my WhateverMBean contains well all that comes from FatherInterface.