Good public relations will create a healthy environment for marketing. But simply providing technical support for marketing is not the same as good public relations. The most effective model of PR involves dialogue and mutual solutions. The commitment of key leaders and asking the right questions are critical. The bottom line is a balance of receivables and payables.
Marketing adds value by increasing income.
Public relations adds value by decreasing the expenses that are necessary when issues are ignored. Faking it doesn't work. Not caring and then apologizing doesn't work. Good relationships are genuine. Marketing and public relations both work best when they're treated as distinct management functions.