A couple weeks ago a federal court delivered an opinion that most (or all) gene patents are invalid: that is, you cannot patent genes. Monsanto's agribusiness profits these days largely stem from their patent of a particular gene which makes soybeans immune to a particular herbicide: RoundUp, which is also a Monsanto product. They have used this gene patent to aggressively corner the vast majority of soybean seed crop sales across the country. Because they own the patent they actually force farmers to sign agreements that they cannot resell the seed without being sued for patent infringement. If that sounds crazy, they will even sue farmers who have never bought Monsanto seed, just for having traces of soy plants with the patented gene present on their land (never mind that the patented gene could travel through, you know, good old fashioned cross-polinization).
Thus, by leveraging patent law, Monsanto has more or less cornered the market on seed for one of the nation's most widely grown cash crops. The challenge to gene patents undermines that legal house of cards and, therefore, Monsanto's profits.