Right, not all of my idea is finalised yet, but here's the basis for it:

In the year 2037 the world has been ravaged by Global warming and pollution, in a bid to defend itself from this the Earth boosts cell development and DNA integrity to all plant life, and giving it a form of intelligence so that it may take back the planet. The surface of the Earth becomes an animated deadly jungle forcing mankind to fortify itself in any cities that it can. Viruses and famine set in and we struggle to survive.

In one of these cities BioChemist Dr Daniel Reed, whilst working with a small sample of the Organic life on a way of communicating with the newly empowered Plants, has a breakthrough managing to converse with the plant life through telepathy, and talks of peace begin.

But communication begins to become weaker and in a bid to keep negotiations going he dons a Mecha suit, built to protect from the dangers of the jungle, and heads out of the city to continue his quest for peace.

But once in the depths of the jungle the telepathic link becomes too strong for him and with the jungles voice constantly in his mind he slowly becomes convinced that man really does deserve what has happened to him. He lets the Organic life bond itself with his suit and his mind, and the symbiotic being "OrgaMech" is created.
With a heavily armoured, living suit, an arsenal of weapons and the power to control all the super enhanced Organic life on the planet he heads back to the city to start the eradication of mankind, once and for all....