This paper investigates the joint transmitter and receiver optimization for the energy efficiency in orthogonal frequency division multiple access (OFDMA) systems. We firstly establish a holistic power dissipation model for OFDMA systems including the transmission power, signal processing power and circuit power from both the transmitter and receiver sides, while existing works only consider the one side power consumption and also fail to capture the impact of subcarriers and users on the system energy efficiency. The energy efficiency maximization problem is formulated as a combinatorial fractional problem which is NP-hard. To make it tractable, we transform the problem of fractional-form into a subtractive-form one by using the Dinkelbach trasnformation, and then propose a joint optimization method, which leads to the asymptotically optimal solution. To reduce the computational complexity, we decompose the joint optimization into two consecutive steps, where the key idea lies in exploring the inherent fractional structure of the introduced individual energy efficiency and the system energy efficiency. In addition, we provide a sufficient condition under which our proposed two-step method is optimal. Numerical results demonstrate the effectiveness of proposed methods and the effect of imperfect CSI is also characterized.