Terraforming through genetic engineering/biocomputers?

Advances in biotechnology are happening daily, and eventually true full-blown biological computers may become the next great computational advancement of our time. Likewise, bioengineering has made leaps and bounds in progress too. Would it be conceivable to genetically engineer plant genes to survive in the harsh environments of Mars and Venus and terraform the atmosphere for human habitation? Or would it be a better idea to design biocomputers with the ability to logically organize their structures for survival on such harsh planetary conditions. The only drawback is that the genotypes of life in both scenarios would presumably have to be radically different than anything we have on earth. Would either idea become practical within the next, say hundred years?