xml serialization specify xmlelement and xmlattribute together

Given :-

[XmlRoot("Book")]
public class Book
{
   [XmlAttribute]
   public string Title;

   [XmlElement]
   public string Publisher;

   [XmlElement]
   public string PublisherReference;
}

When serialized to XML will give

<Book Title="My Book">
   <Publisher>Some Publisher</Publisher>
   <PublisherReference>XYZ123</PublisherReference>
</Book>

How could I get PublisherReference as an attribute of Publisher - e.g.

<Book Title="My Book">
   <Publisher Reference="XYZ123">Some Publisher</Publisher>
</Book>