GRAINS-Rain forecast for U.S. Plains drives wheat to one-month low
* Wheat down for second week as U.S. Plains set for relief * Soybeans ease from near 7-year high, S. America weather eyed * Corn subdued as U.S. planting indications awaited (Updates with European trading, changes byline/dateline) By Gus Trompiz and Naveen Thukral PARIS/SINGAPORE, March 12 (Reuters) - Chicago wheat futures extended losses on Friday to a one-month low as rain forecast for dry parts of the U.S. Plains eased supply concerns. Soybean edged lower as it moved back from a near seven-year high this week,