MF Global: UPDATE 1-PwC threatens MF Global mistrial; Corzine defends actions

NEW YORK, March 13 (Reuters) - PricewaterhouseCoopers LLP on Monday said it may seek a mistrial in a $3 billion malpractice case over the collapse of Jon Corzine's MF Global Holdings Ltd, saying it was blindsided when the plaintiff changed its theory of why the brokerage failed.