Subject: how do the mitochondria and the nuclei communicate with eachother?

the reason why i am asking this question is because i learned that the 
mitochondria have their own set of dna separate from the nucleus. i was 
wondering how this is possible if for example, when people get transplants 
such as kidneys and etc, their body reacts to it and rejects it, and that is 
why people who have transplants die after a while. how is it possible for the 
mitochondria to work and survive and communicate with the cell when it has 
different dna, and yet not get rejected by the cell? i was also wondering if 
you could tell me how much one molecule of atp is worth, as far as energy is 
concerned. i would also like to know what exactly is mitochondrial disease. 
thank you very much for you help.

Re: how do the mitochondria and the nuclei communicate with eachother?